TAT and Takeoff Thrust in the 777

Recently I witnessed an interesting occurrence on the line that has resulted in a number of queries to Boeing, and while not all the answers are back, the results so far are fascinating. Eighteen years on the aircraft and still learning, which is actually a nice place to be.

Disclaimer : Normally I try to produce content to engage readers across the spectrum from those with an interest in Aviation through avid Simmers through to other Professionals operating the 777. In this case, the following is unashamedly technical and I apologise if I lose you on the way through – each time I re-read it, I lose myself and change it again!

We were parked on stand in Melbourne (YMML; Stand D20) getting ready to go to Los Angeles and while the ambient temperature was 19° and a light northerly blowing, we were heavily loaded and full thrust was going to be required – Melbourne has some hills to the north which reduces the weight you can lift, despite a small headwind component. As the temps get higher in Melbourne, you can get into a weird situation where you’re better taking a small tailwind away from the hills off Runway 16 than a small headwind towards them on Runway 34 – but I digress … for this sector, I was in the jumpseat, conducting an Annual Line Check on the two operating crew members.

During entry of the takeoff performance into the FMC (Flight Management Computer) by the Captain, I noted a disparity between the N1 specified by the Takeoff Performance Calculation (TLDC); and that calculated by the Flight Management Computer.

While the TLDC (Takeoff Landing Data Calculator – the computer software we use to calculate takeoff and landing performance) calculates the N1 that we’ll be using for takeoff – in actuality, the performance calculation specifies a Fixed Thrust Rating (TO, TO1 or TO2) in combination with an Assumed Temperature value.

We enter these TLDC calculated Thrust Selections into the FMC and in conjunction with the entered weight and aircraft systems sensed ambient conditions (temperature, pressure) – the FMC calculates the target N1 for takeoff.

There is almost always a small difference between the value calculated by the FMC and that calculated by the TLDC computer. This comes down to several factors, one being that the Airconditioning Packs prior to takeoff are working at full capacity; whereas they are reduced to a low flow rate during the takeoff roll. This leaves more thrust available for the engine, resulting in a different N1 calculation result. The TLDC computer is aware this is going to happen and calculates accordingly; the FMC modifies the Target N1 once the Packs are reduced during the roll.

On this day – the difference was more than “normal” – about 1.5% with the FMC calculating a lower value (which typically calculates a slightly higher value). Our SOPs note the difference but have no crosscheck or tolerance as such. In the past, I’ve seen this occur when the ambient temperature is higher on the aircraft gauges than the Airport Weather Service (ATIS) is giving. While we use the ATIS reported temperature in our (TLDC) calculations for N1; the FMC can only repeat the calculation of N1 by referring to the temperature “felt” by the aircraft and reported through the TAT (True Air Temperature) probe. In this case – the TAT indication on EICAS was 37° as against the ATIS 19°. That explained the N1 difference – but not why the TAT indication was so high.

N1” is engineering nomenclature used to refer to the rotation speed of the First Rotor – in our case the big fan you see at the front. Broadly speaking the rate of spin of this fan is equivilated (another engineering term) to Thrust. The GE90’s have two engine spools, the second of which is (of course) called the N2. The 777-200’s I used to fly had Rolls Royce Engines with three spools, so of course, there was an N3. On modern high bypass engines, the N1 is essentially a huge fan (not terribly dissimilar to the Propellors of old), rotates the slowest, produces most of the actual thrust, and is driven by a connected turbine in the exhaust gas flow at the rear of the engine. The N2 (and N3) spools are all about compressing the air (intake) and extracting energy from that air on it’s way out the back end after that air is burnt in the depths of the engine casing.

N1, N2 and N3 values are given as percentages (for example Red Line Maximum N1 for the GE90’s in my aircraft is 110.5%) because their spin rate differs vastly. The big fan at the front averages 4000 RPM during takeoff; the little one in the middle closer to 13,000. As to why maximum speed is not 100% – I really have no idea, it’s never made sense to me for them not to callibrate things that way. It just is.

The Captain remarked on the N1 difference and we noted the high TAT reading. I’d seen this before when parked and airflow is poor through the TAT probe; but we were facing the Terminal (East) and the probe was actually in shadow, so it still seemed odd. We resolved to re-examine the TAT during aircraft push and engine start; hopefully, the TAT indication would assume a more appropriate value.

TAT is the measure of Total Air Temperature, as measured by a dedicated probe on the outside of the flight deck (Aircraft TAT) or just inside the top of the two engine nacelles (Engine TAT). It’s called Total Air Temperature because at speed the temperature measured reflects the combination of Outside Air Temperature (OAT, somtimes referred to as Static Air Temperature, SAT) and the temperature rise that occurs when air molecules are smashed against a fixed probe racing through the atmosphere at 800 kph. At 35,000 ft the OAT can be -56°C wheras the TAT can 20-30° warmer.

On the ground, the TAT indication is considered a valid measure of OAT, but caution has to be exercised if you’re going to use it to second guess the airport ATIS temperature. The temperature reported by the ATIS is essentially a certified value, taken at a specific location, behind a Stevenson Screen, monitored, crosschecked, etc. The TAT probe … is not.











Meanwhile, I started to think about the problem of the numbers we were seeing and what impact it might have if the TAT did not drop down. The TLDC had told us that MaxT (the maximum temperature we could accept to be able to take off with our present load) was 29°, so it seemed to me that the TAT remaining well in excess of that was likely to cause us problems.

Engine start and aircraft pushback did not actually improve things:

  • During Engine Start, that TAT indication remained high.
  • After Start, we received an FMC Scratchpad Message V SPEEDS UNAVAILABLE (“For certain high thrust/low gross weight takeoff conditions, FMC VSPEEDS are not calculated. Adjust gross weight and/or takeoff thrust limit to enable VSPEEDs.“)
  • Our previously entered speeds remained in the FMC and displayed correctly on the PFD.
  • The FMC CDU Thrust Limit Page was basically completely blank (headings only)
  • The Target N1 was removed from the EICAS N1 displayed.

But the temperature had dropped a few degrees with the Engine Start, so we decided to continue the scenario (looking behind us to make sure there was no Sim Instructor and this was not a Simulation …) and commenced taxi. During taxi, the TAT indication continue to reduce.

As it dropped below 28° …

  • The CDU cleared the V SPEEDS UNAVAILABLE message, replacing it with “TAKEOFF SPEEDS DELETED” and our Takeoff Speeds dropped out of the FMC
  • The previously selected Thrust calculations returned to the CDU Thrust Limit page and the EICAS N1 gauge.

We re-entered our performance data from scratch, double checked everything and proceded for a normal departure. As we commenced the roll I noted that the EICAS was targetting an N1 of 105.5; whereas the TLDC had recommended 105.2 – which seemed pretty reasonable. Interestingly while the TAT had reduced on taxi down to the ambient 20°; it then began to increase while we sat at the holding point and re-entered the takeoff performance. During the takeoff, it reduced once again with airflow until increasing again as is normal with increasing airspeed. The FMC N1 target adjusted accordingly to these variations.

As a footnote – we became airborne normally and survived.

As is often the case – the follow up has been informative and not completely satisfying. I pursued this with our Technical Department, a contact at Boeing Propulsion, and the Flight Training/Standards and Technical Departments at three other 777 operators. So far, I have the following:

  • The N1 gauge on EICAS includes a Red Line Limit (maximum rotation 110.5%); the Amber N1 Max; the Green N1 Target; the White Arc N1 Commanded; and the White Line N1 Actual.
  • The N1 Amber indication represents N1 Max – the max rated value of the N1 for the current flight conditions. This is the value that would be commanded if the thrust lever is placed at the max forward position, as limited by the EECs (Electronic Engine Control) operating in Normal Mode.
  • The value of N1 Max, Commanded N1 and Actual N1 (to a lesser extent*) is computed by the EEC using the selected TAT source, which is normally the aircraft TAT (as displayed on EICAS) as long as it is within 2.5° of the engine TAT. In the case of a large disagreement (>5°), the EEC will select its own onside engine TAT sensor in the calculation of N1 Max. Between these two values, the selected EEC value linearly ramps the value used towards the engine source. The value of 2.5° was selected as it corresponds (on a hot day) to an amount of thrust error that is small enough preserve the acceptable operation of the engines.
  • If the EECs are in Hard Alternate Mode, the EEC computed N1 Max is set to invalid, so the displayed N1 Max is subsequently computed by the TMF (Thrust Management Function) of the FMC – using aircraft TAT.
  • On takeoff, after 80 knots (at a constant thrust lever position) the Commanded N1 automatically changes as temperature airspeed and then altitude increases after liftoff. The EEC and TMF both calculate the N1. The TMF target (Target N1), the EEC Commanded N1 vary automatically during the takeoff as a function of airspeed and altitude. There are a number of considerations such as engine temperature/pressure and other factors that determine the precise N1 variations to provide optimum performance and engine life.
  • As such, the aircraft TAT is used throughout the takeoff to determine the N1 values by the TMF and the EEC.
  • * In most cases, the Actual N1 is independent of sensed TAT in the thrust lockout period during takeoff, but it is possible for a significantly elevated TAT (such as during a Temperature Inversion) to affect the indicated N1 as well. Note that engine TAT sensors are not used to compute the TMF N1 Target.
  • There is a cross-check between Aircraft and Engine TAT – if the difference exceeds 15°,  then the air data is declared invalid for use by FMC and TMF, the thrust ratings will go away, the CDU Thrust Limit page will blank, and there will be no performance predictions.
  • There is also some magic going on in the conversion from “corrected” N1 to “physical” N1 that is relevant to this discussion, but I’ve yet to find any clear definition of what’s going on with that. More magic I presume.

What does all this mean? Good question. As far as I can determine, the above summarises into:

  • Target N1 is calculated by the FMC and is dependant on Aircraft TAT.
  • Commanded N1 and Actual N1 are calculated by the EECs, which use the Aircraft TAT unless the difference between Aircraft and Engine TATs become significant, in which case the EECs bias towards – and then slave off of – the specific Engine TAT probe.
  • All the values of N1 Max, N1 Target, N1 Command and N1 Actual are subject to the influence of a false TAT reading to one degree (!) or another.
  • A false reading of more than 5 degrees in the Aircraft TAT would impact the N1 Target, but not Commanded/Actual N1
  • A false reading of more than 5 degrees in the Engine TAT would affect the EEC Commanded and Actual N1 (affected engine), but not the Target N1.
  • There’s a whole lotta magic going on

In the aftermath of this, I notified Engineering and while I lost track of the story, I believe another crew experienced a similar occurrence and a problem with airflow through the TAT probe was identified, and corrected. What is impressive in all of this is how well thought out the system involved is, and the technical depth and forethought that goes into account for all the possible things that might go wrong in something as crucial as calculating thrust for takeoff. It speaks to decades of experience in development at GE and Boeing, and it’s awesome.

Wide Body EBA 2017 Calculator [UPDATE 27Nov18]

With the implementation of the 2017 Wide Body EBA – it’s time to revise the spreadsheet I developed to track and check Overtime, Callout, etc for the 2011 EBA. Part and parcel has been seeking clarification from the AIC/CP on certain aspects of the EBA’s implementation. Most particularly clarification over the MCG, how RP changeovers are going to be implemented and how they impact the credit hours associated with Duty Periods and Flight Duty Sequences (MCG) that take place over the RP changeover to the next RP. I believe I have the answers now, the spreadsheet is in beta; welcome to the test program!

Note : Some the images here may look a little small – but if you click on them they expand to a decent size over the text.

Note : The Allowance Calculator requires Visual Basic. This means it does not run properly on MAC or IOS (iPad). You can use your Mac/iPad to enter the list of duties, but the Payslips tab requires a custom function I wrote to work. You can use the Excel in Citrix, or if you have a PC you can get Office Pro as a Virgin Employee quite cheaply – ask me how.

Version History

27Nov-2018 : RP13/01 has just been published with RP01/2019 starting on 31DEC18. Fowl Ball! How can you start an RP on the 31st of the year before? It should have been RP1314. I think they did it just to annoy me. Anyway – manual fix required in this version to accurately reflect RP1301/2018 (and RP0203/2019, etc). Download HERE.
18-Oct-2018 : Updated for ATO Domestic and International Allowance Changes.
21-Mar-2018 : Whoops – previous upload had my roster in it!
09-Mar-2018 : This release fixes a coding error that I missed in my review of the EBA. When called out for a Non (Flight, Sim, Standby) duty – you are paid the Callout but not creditted any overtime value. The sheet now allows this and inserts “OT+CO” where the normal credit for a Non (Flight, Sim, Standby) would be paid. There are a few other changes so – “Positioning” has become “Position Only” and “Away Day” is now “Away/Blank Day”. I’ve also highlighted the use of “Positioning (FRMS)” in the positioning area to show no credit … 
22-Feb-2018 : Made some minor formatting corrections, and changed “Away Day” to “Away/Blank Day” (Thanks Tim)
29-Jan-2018 : Added the ability to enter duties/periods and calcluate allowances to see what you’re getting on an overnight, and to crosscheck your payslip. There are some other minor changes to the OT/Callout sheets (both fleets) as well that do not affect the calculation result. I’ll add some instructions and a few videos for this at some point
26-Jan-2018 : Found some bugs in the new A330 sheet. Basically it wasn’t calculating Carry-Out Flight Pairings correctyly.
22-Jan-2018 : Updated 2 Operating sectors for the A330. Tidies up the conditional formatting in cells to more appropriately highlight cells that should have data (Green) and cells that really should have data (Yellow). Also Combined Position/Operating route into a single cell eg: “MEL-BNE” – note this means that the instructions below aren’t quite matching the spreadsheet for the moment.
20-Jan-2018 : Update for the A330. There’s now an A330 tab in the sheet. Please advise if it’s working ok!
09-Jan-2018 : Initial Issue.

Video Tutorials

The following video covers Entering Your Roster.

This next one covers entering Actual Hours for Positioning/Flights and entering Callouts and Changes …

This next one covers Carry Out Flight Pairings (including MCG) and Carry-In Flight Pairings.

Finally – the A330 Differences in the sheet.

Late addition – Entering Duty Periods and Checking Payslips for Domestic and International Allowances.


As usual, the sheet copes with Ranks, Salary Levels and Years in terms of the changes to the various values of Overtime, Callout, Ad Hoc Training Pay and more through the life of the EBA (noting that the last 3 year EBA lasted about 7 years). If you peek into the Data tab, you’ll see the A330 stuff in there as well. An RP calculating sheet in the same Excel file for the A330 is my next task. If you’ve used this before – you’re in for a mix of the familiar and the startlingly new …

Note : While the sheet does both the A330 and the B777 (on the 2017 Wide Body EBA) only the 777 is described here. At the moment the A330 sheet only handles one sector per day but I will fix that shortly. Other than that – the instructions are valid across both fleets (I hope).

  • Ranks : It does Captains, First Officers, and Second Officers. The 2017 EBA has levelled the playing field in terms of Checkers/Trainers and OT and Callout, so there’s no longer the need to differentiate.
  • Levels : Whether you’re Level 5 or Level 1 – you select and the sheet does the rest.
  • Level Changes : On 01 July each year, your Pay Level increments. Therefore the Overtime/Callout rates increase also. The sheet copes with this.
  • A330 Odd/Even SN : The A330 has a different number of min days off each RP, depending on whether you are an odd or even staff number. Seriously? Anyway I’ve added this to the A330 sheet so the min DDO’s calculates correctly.
  • Duty Select : You don’t have to know credit hours – just select the duty for each duty day and the sheet will use the relevant EBA Credit Hours.
  • Leave : Leave impacts the Overtime Threshold, as well as the minimum number of days off required in the month – the sheet copes with this.
  • Positioning : Positioning changes a bit, with the introduction of a 1 hour sector minimum, 50% basis for credit hours and 2 hour minimum for position only duty periods. As always the maximum of Scheduled vs Actual is the basis for calculation so you’ll need to track and enter both. I’ve also added the ability to Position (FRMS) after going fatigued so the credit hours won’t count.
  • Ad Hoc Training : When you’re not a Check/Training Captain, but conducting Ad Hoc Training as an Instructor (eg : NTS) – there’s a credit and payment. The sheet tracks this as well.
  • Data Filtering / Validation : As much as possible, cell entries are checked from lists for validity (Duties, Airports, Yes/No’s, etc). Any time this is done – there’s a list box you can click to drop and choose from.
  • MCG : The Minimum Credit Guarantee of 5 hours for each day of a sequence of Duty Periods that takes you away from Home Base and includes an operating crew Flight Duty Period (FDP). This was a little tricky to implement, and I’m not sold on my method – suggestions welcome!
  • Carry-Out : Individual Carry Out Duties are no longer necessary – any single duty period that has a credit value (ground or flight) that commences prior to midnight (Crew Local Base Time) on the last day of an RP – the credit hour value for that duty period is paid in that originating RP. Also…
  • Carry-Out DPs/FDPs (including MCG) : Any series of duties (must include an FDP) that carries into the following RP are credited as a whole into the could well result in an MCG based additional payment in the originating RP. Therefore in order to track and calculate this, you’ll need to enter all the Duty Periods past the end of the current RP at the bottom of the sheet in order to ensure the DP/FDP credit values are added and the any applicable MCG calculation is checked.
  • Comments : So you can stir the memory every 8 weeks without having to come back here, many of the cells include comments to remind you how to fill them in or the function they perform. These comments are indicated by the small red rectangle, and pointing your mouse at them causes them to popup.
  • Cell Color : Cells are color coded to assist in entry. Generally only cells coloured GREEN are where you should (can) enter data. Sometimes a cell will be coloured YELLOW to indicate that either no entry has been made (and one is required); or to highlight the use of that cell to you (such as to override a calculated value).
    In the example show, because Positioning has been selected, the Sector field is yellow indicating an entry required, and the Scheduled and Actual Block Times fields are green, also awaiting entry. Note the EBA Credit field is white and is a calculated field you cannot enter data into. Meanwhile, the Over Ride field is also green in case you want to over ride the calculation. Similarly, on the Flight line, the FromToScheduled and Actual Block fields are yellow, awaiting the details of your flight duty.
  • Error Checking : There is a comprehensive cross check built into the sheet to try and ensure you have completed it correctly. If an error is detected (such as a day you forgot to fill in) the “Error” box in the top LH Corner of the sheet. Further, there will be an error flag at the end of the row that contains the error. Finally, the cell in error (might) also be red/yellow to indicate a problem.

1. Primary Selections

  • Choose your Rank (Capt, FO, SO). This influences rates for Callout, Overtime, etc.
  • Choose the Pay Level/Year applicable at the end of the RP. You’re paid after the RP completes, so if there’s a changeover of rates (01 July each year) then the rate applicable after the change will be the ones used,
  • Select the Roster Period.
  • A330 Only : You need to select whether you are an Odd or Even Staff Number (SN). This impacts the calculation of your Min Days Off for the RP.

Having made these basic suggestions, the Overtime Threshold, Effective Overtime Rate (paid after the RP completes) and the Callout Rate are displayed. Note that the OT/Callout rates are based on your Pay Level/Year selection, and the OT Threshold includes the vLearn credit in each RP. The Error flag is shown because the selections against the days of the RP are not yet complete.

2. Daily Duty Types

So the main sheet is where all the work happens, of course. You must select a duty type for every day in the RP – even days where you didn’t do anything, or days that don’t exist (such as the one between takeoff and landing on the way back from LA).

Select the cell, then click the little drop-down arrow to see the list. You can also just type in the entry you want (you must spell it correctly!). Note that having selected it once, the next time you can just start typing the entry, and Autofill will quickly work out what you are after. This seems to be the best way.

Strictly speaking, the days in the column on the LHS of the sheet are based on Crew Member Base Local Time. So when you assign a duty or flight down route in LAX – you should be selecting the Australian Date for this duty. In practice, this only comes into play for carry-out flights/duties at the end of the RP – and this area has been tidied up immensely since EBA 2011.

Shown here is the current list of duty types in use. These may change from time to time, but so far these have worked from the previous EBA.

  • Admin Duty : Admin duties that come with the standard 5:00 hours credit
  • Admin – No Credit : Used when doing an admin duty that does not credit you towards Overtime (0:00)
  • Away Day : Basically days away down route that are not days off. Also the day between departing LAX and arriving back into Australia.
  • Day Off : This is your DDO’s and ADO’a. Note that sometime Crew Control will convert a duty to a Blank day as the result of a change. This is basically a Day Off that won’t generate a callout if you subsequently work it.
  • Flight : Select for any Flight Duty Period (FDP).
  • Gnd/Trg Duty : Basically any type of Ground or Training Duty that’s not Admin – SEP, NTS, etc. This includes running such courses.
  • Leave (All) : All types of leave that reduce your OT threshold, including Annual, Parental, Carers, etc.
  • Open Day : This is the 12 hour notice, 3 hour credit standby day that came in with the 777 2011 EBA. Love these.
  • Positioning : Any form of positioning, where the positioning is the only duty undertaken that day. The sheet automatically handles the 50%, minimum 1 hour per sector; minimum 2 hours for position only duty days.
  • Position (FRMS) : Positioning in the event of going fatigued may not attract credit. Check the EBA whether this applies to your positioning after going fatigued and if so, select this duty to calculate your credit hours correctly without the credit for FRMS Positioning.
  • Sick : Sick days do not attract credit and do not reduce your credit target.
  • Sim Instructor / Sim Student : These two duties have different credit values.
  • Standby/Reserve : This is applicable to both Standby at home and Hotel Standby.

3. The Simple Duties – as well as Callout, Ad Hoc Training and Cancelled Accommodation.

So some of the duties (Flight, Positioning) are clearly more complex than others. Let’s get the simple ones done first.

  • Day Off ; Admin (both); Gnd/Trg Duty; Leave; OpenDay; Sick, Simulator, Standby/Reserve : Once selected, that’s it for that day … except if …
  • Callout : If a callout is applicable, you need to Enter or Select Yes in the callout column. Note there is no longer  Day One, DayOne+ callout rate – it’s all one rate.
  • Ad Hoc Trg : If you’re performing a Gnd/Trg Duty as an Ad Hoc Instructor – enter Yes in this column to have the sheet calculate your Ad Hoc Instructors payment to the breakdown/total.
  • Canc Accom : If you have cancelled company accommodation for one or more duties, select Yes here to have the sheet include these in the breakdown/total.

4. Positioning

Positioning requires additional detail to calculate correctly. The (basic) EBA 2017 rules for calculating Positioning Credit are as follows:

  • Positioning typically gains a 50% credit of the larger value of (Scheduled or Actual Block Time). Once again – prior to positioning the Flt Time value on your roster is the Scheduled Block Time; once you’re positioned your roster will show the Actual Block Time.
  • There’s a minimum 1 hour credit per sector (applied after the 50% factor).
  • If the only thing you are doing in the duty period is Positioning – then there’s a minimum 2 hour credit.
  • Remember that if you commence a Duty Period with Positioning (or anything else) that goes over midnight Crew Base Local Time of the last day of the RP and into the next RP – the credit (Scheduled/Actual/EBA) goes into the RP in which the Duty Period commenced.
  • There are some very specific instance where International Positioning in Economy comes with 100% of the (Scheduled/Actual) hours as Credit. In this case – the EBA Override cell is used to credit yourself with the full sector’s credit.
  • Clear as mud?

Here you can see a typical series of duties. Day One is positioning up to BNE for Simulator. Day Two is the Sim Session, and (yet to be entered) the positioning sector home. Note the Yellow cell showing a required entry (the sector) and the three green cells for Sched BlockActual Block, and Over Ride. The EBA Credit is already filled in at 2 hours minimum since that’s all you are doing during the duty period.

Now the first line is basically complete. The sector (MEL-BNE) has been entered. The Sched Block (from roster publication) has been entered. The Actual Block (from the roster after “flown”) has also been entered. Since 50% of both these values is less than 2 hours – the EBA Credit remains at 2 hours. Note that any value you enter in the Over Ride cell will over-ride the EBA Credit cell. Any value you enter in this cell turns the cell Orange to indicate that an over-ride is in use.

But we have to get home from BNE after sim. This positioning is part of the Duty Period applicable to the Sim Student duty. To apply this, click on the Sector cell and enter the BNE-MEL sector (even though the cell is not green). Once you’ve done this, the Sched BlockActual BlockEBA Credit and Over Ride cells will activate for further entry. You can see that in this case the 50% credit value is calculated (since there is no 2 hour minimum) and that Actual is great than Scheduled. If this was SYD-MEL, the EBA Credit value would show 1:00 since 50% of SYD-MEL is less than the one hour per sector EBA minimum.

Finally – in the event that we go fatigued after a duty and are not safe to drive home, any positioning sector that follows the rest may not incur a credit value. In this case, show the duty as Position (FRMS) and whatever you choose to enter in the Sector,  Sched BlockActual Block cells – the  EBA Credit cell will show 00:00. Note however that the Over Ride cell still functions to override all calculation and uses the entered Over Ride value to credit your hours.

One case the Over Ride cell could be used is when positioning internationally on a sector length above 7 hours where the rest period after the positioning, prior to operating, is less than the minimum proscribed in the EBA. In this case – manually enter the maximum of (Scheduled ActualBlock Time into the EBA Over Ride cell – there is no factoring here, any value you enter over-rides all other positioning considerations. In this case the EBA Over Ride cell shows in orange to indicate it’s over-riding all the other positioning calculations.

Note : Occasionally you have to do mental maths to work out the Scheduled or Actual Block time from your roster. If you have a Start and Stop time for this, you can do the maths in your head (remember the two times are Local Time so between MEL and BNE there could be a missing (or extra) hour you have to account for in your formula) – then you can use the following formula in Excel (say the Actual Block is between 14:37 and 16:58) in the cell where you need the result. After you’ve used the formula to get an answer – it’s easiest just to type the answer in over top of the formula.


4. Flights

Flights also require more details in order to calculate the correct credit value. This includes tracking both Scheduled and Actual Block Times (Pushback to Park). Note that the Flt Time value that appears on your Sabre roster at publication (or before you fly the trip) is the Scheduled Block Time applicable for the trip. Shortly after you have flown the trip – this time becomes the Actual Block Time you flew – and the Scheduled value is no longer accessible. I therefore strongly recommend taking screenshots of your roster after publication so you can retain the scheduled values.

MCG : Minimum Credit Guarantee

More complicated is the implementation of the Minimum Credit Guarantee. Basically when you head off from Home Base on a series of duties that includes a Flight Duty Pairing where you are operating (not positioning) – you get a minimum credit of 5 hours per day until you complete the Duty Period that signs you off at Home Base. This includes any Duty Types (Simulator, Admin, Ground Training, Open, Standby, Day Off, etc) as long as one of them is a Flight (Operating).

At the end of the duty series – if the 5 hour per day credit exceeds the credit from the Duty Period/Types – you are paid the MCG. I’ve implemented this methodology using the MCG # column to the immediate right of the Duty Type column. Anytime you start a series of flight-related duties (1 or more) where the MCG is applicable (because of a Flight) – place a number in the MCG # cell for each date of the sequence of duty periods. Keep that number identical for subsequent duties until complete the series ends back at Home Base. Use a new number for the next series of duties that includes an FDP. It sounds more complicated than it is … Mostly.

Firstly select Flight from the Duty Type list box on the left against the departure date of your flight. Note that technically this is the departure date based on your Crew Base Local Time. Which for evening LAX departures means the day after that shown on your Sabre roster.

  • Now enter the MCG # value. While the specific number actually doesn’t matter (I’ve limited it to 1…9 for now) – I suggest using 1-1-1-1 for your first trip; then 2-2-2-2 for your second trip, etc. Note that when you select Flight the MCG # cell next to that selection will turn yellow to highlight you need an entry there. When you choose a non-flight for the next day (say, Away Day) the cell will not be yellow – but this cell still needs the MCG # since it’s part of a sequence of duties.
  • Next, scroll across and you’ll see the Flight Details area has some yellow areas for entry. Enter the From airport and the To airport, then enter the Scheduled Block time (shown on your Sabre roster as Flight Time at publish). This will give you an initial estimate of the credit hours that will come from this duty. For the moment I have not provided for multiple sectors on the 777 – I’ll do it with the 330 and then decide if the solution should be rolled back. Further to the right, you can see the EBA Credit has your scheduled block time value.
  • Once you’ve operated the flight, look back at your Sabre roster and enter the actual Flight Time into the Actual Block time in the spreadsheet. If Actual was longer than Scheduled – you’ll see the new, larger value in the EBA Credit cell.
  • Remember that if you’re called off one or more days off for a trip – enter Yes into the Call Out cell to the immediate right of your Duty Type selection.
  • Finally, once again remember that if you commence a Duty Period with Positioning (or anything else) that goes over midnight Crew Base Local Time of the last day of the RP and into the next RP – the credit (Scheduled/Actual/EBA) goes into the RP in which the Duty Period commenced.

After the entries are complete, scrolling further across to the right (see below) you can see the Duty Type Credit (Max of Sked/Actual Block); MCG Cumulative Credit (5 Hrs/Day), the Pairing Cumulative Credit (based on Max of Sked/Actual Block); and MCG Additional – in the case above the credit from the flying exceeds the credit from the MCG, so there’s no addition. Let’s hit all the highlights with the next one …

Final Example – Flight with Callout, Positioning, Standby and MCG

The following is an example where the MCG applies – in this case, the shorter BNE/LAX flight times (after Standby), along with an extra day in LAX brings the MCG into play. Since the MCG Accumulation (7 x 5:00) comes to 35:00 while the Sequence of FDP related duties comes to 33:00 – there’s a 2:00 in the MCG Addition column at the end of the MCG sequence, and this 2:00 extra has been added into the EBA (& MCG) column on the far right. The MCG is paid by the spreadsheet against the last day of the sequence – either as the only credit (if the last day has no credit, like an Away Day) or added to any credit on that day – like in this example where the 2:00 is added to the Positioning Credit of 1:10.

This sequence is positioning to MEL-BNE for Standby, then heading off on a 5 day trip to LAX (you never know …) then coming back to BNE and positioning BNE-MEL home after arrival. Note in this instance I was called out for this sequence as indicated by the Yes in the Callout column.

  • The MCG # (2) is selected for the entire set of the MCG related days. Because the Positioning and Standby days are associated with the Flight Duty Period sequence – they count towards MCG. The “2” probably means this is the second trip on my roster.
  • Positioning on 28/Jan was 2:00 because that’s the minimum. Although the MCG of 5 hours on the day exceeds this value – MCG applies across the total sequence of duties, so you can’t tell if MCG is going to pay until it’s all over (including Actual vs Schedule for both Positioning and Flights).
  • Standby on 29/Jan has a 5:00 hour credit.
  • The Flights on 30/Jan and 02/Feb are credited based on the highest of (Sked/Actual) Block Time.
  • During the sequence, the highest of the MCG Cumulative Credit or Pairing Cumulative Credit is highlighted (subtle yellow).
  • At the end of the sequence – the MCG accumulation comes to 35:00; the duty related credit 33:00 – so the MCG adds 2:00 hours to the EBA (& MCG) Credit for the series of Flight related duties.

Note that while the EBA may not be clear – the Payroll system is coded to look only for an FDP as part of a series of duties; then it looks for the first Duty Period that took you away from Home Base at or before the FDP; and the last Duty Period/DFP that brought you back to Home Base. MCG is applied across the entire series of duties – FDPs and non-FDPs alike.

In the example below, I choofed off to Sydney on 02/Jan to teach two days of Ground School. Then I headed off SYD-LAX and came back the next day. On the last day (after arriving into SYD) I positioned home to MEL. The MCG calculation is done across all these duties. In this instance MCG Cumulative Credit is less than Pairing Cumulative Credit.

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EBA Overtime Calculator (v2.6) [Update 27Oct17]

I’ve watched the EBA with some envy for the last three years. Between Overtime, Callout, Domestic Allowances, Leave and Days Off, the position of Manager hasn’t quite kept pace with the EBA. I’ve also been watching the need for a spreadsheet to calculate the Overtime, Callout and Accommodation Cancellation monies, but resisting the temptation to build one. I didn’t quite want to know how much I was missing out on.

Current Version : V2.6 27.Oct.17 : Down HERE.

– Corrected for leaving the wrong cells locked in 2.5 – no other changes.

I really would have thought we’d be on the new EBA by this RP, but apparently not? Anyway – 2.5 extends the sheet for a couple more RP’s just in case. Esp since there’s still seems to be a lot of overtime going around, even with an aircraft in maintenance for most of this RP …

– Ok, so after some discussion at a recent EBA meeting, positioning credit/before after duties (1 hour) is going to be paid for the time being. Meanwhile the lack of any payscales after 01Jul17 has broken my spreadsheet. For some reason I didn’t plan for the 3 year EBA of 2011 to still be in force …  fixed in 2.4

– After years of paying it, the company is now no longer paying a 1 hour credit for positioning before/after any other duty. Until recently, the 6 hours or so added to my day that is positioning up to BNE for Sim/Admin/etc is not worth Zero. The interpretation is that this event is “travelling” before/after a duty and not positioning under the EBA. Yeah right.- Positioning BNE/SYD/MEL no longer carries a 1 hour credit unless it’s completed as it’s own duty.
– Corrected adding error in Block Hours Total (Top RHS)
– Thanks to PM for spotting to bugs that I’ve corrected in V1.5
– Thanks to TH removed Super from Salaries to better compare Overtime with payslips in V1.6
– Now deals with Carry In/Out Flights that wrap from one RP to the next (see below) – V1.7
– Bug correction in Carry In/Out Flights & Updated to clarify that Push/Park are for Sked; Actual (was User) is for Actual Block (Tks TD) – now in V1.8
– Corrected Calc Blocks Time not showing 00:00 for midnight V1.9
– Added BNE/MEL positioning; change to allow for zero credit positioning on same day of Duty V2.0
– Added CCA/TCA/TFO Rank Selectors to incorporate appointment pay in overttime V2.1

The combination of recently updating my Tax Allowance Claim Calculator for the 2011/2012 Tax Year as well as seeing someone else’s overtime calculation sheet come past my inbox, I decided it was time to get off my tail and build one. I also decided to see how much I could test the data validation and conditional formatting functionality of Excel and turn it into a custom form like entry interface that would test and indicate both incompleteness as well as validity of entries. In the past I’ve always tried to maintain compatibility with Excel 2003, forgoing the really cool features of Excel 2007/2020 – not anymore.

VAI 777 EBA Overtime Calculation Spreadsheet.

I wanted my sheet cope with the following aspects, all in a single spreadsheet.

  • Ranks : It does Captains, First Officers, Relief First Officers; Check Captains, Training Captains and Training First Officers under the EBA.
  • Levels : Whether you’re Level 5 or Level 1 – you select and the sheet does the rest.
  • Level Changes : On 01 July each year, your Level increments. Therefore the Overtime rate increases also. The sheet copes with this.
  • Duty Select : You don’t have to know the credit hours – just select the duty for each duty day and the sheet will use the relevant EBA Credit Hours
  • Leave : Having Leave impacts the Overtime Threshold, as well as the minimum number of days off required in the month – the sheet copes with this.
  • Positioning : There are two types of positioning – EBA (MEL-SYD-MEL or BNE-SYD-BNE) and All Others. The EBA has the standard credit hours – the rest you have to enter. The sheet uses the default credit for EBA positioning; facilitates your entry of the Block hours for non EBA positioning (SYD/KUL/SYD).
  • Ad Hoc Training : When you’re not a Check/Training Captain, but conducting Ad Hoc Training as an Instructor (NTS) – there’s a credit and payment. The sheet tracks this as well.
  • Data Filtering / Validation : As much as possible, entries are checked from lists for validity (Duties, Airports, Yes/No’s, etc). Anytime this is done – there’s a list box you can click to drop and choose from.
  • Summaries and Analysis : Once complete, quick reference summary at the top for Days Off; Leave; Sims; Admin; Standby/Open; Ground Duties; Credit hours (in relation to the Overtime Threshold); Callouts; Block Hours; Cancelled Accom and Ad Hoc Trainer. There’s also a list of duties with a count on the far right, and I’m playing with Pivot Tables and Charts in this one too.
  • Variables ?: I’ve coded as much as I can as variables that can be changed should I need it to. I can’t see anything changing in the EBA in the next 12 months – but just in case …

Let me run you through how to use it:

1. Basic Entries.

The first things the sheet really needs to know is your Rank (Capt, FO, CRFO); Pay Level (1 … 8); and which Roster Period you are looking at (currently only from RP 2012 3/4 onwards). Note that Rank now includes choosing Check/Training Captain/First Officer since this impacts some values.

Note that the Pay Level is the one at the start of your target RP. For most of the original VAI pilots that will be level 5 from RP 9/10 2012 onwards.

Note that when you point your mouse at a cell with a little red triangle in the corner – a hint pops up. Also not that when you click into a cell for data entry – if there’s validation on the cell (such as the requirement to select from a previously established list) a small down arrow shows to the bottom right of the cell – click the example here to see.

Having chosen these variables, the initial credit threshold (it will updated as Leave days are later selected) and Initial Overtime Rate should be checked. All the Dates down the LHS should also fill in for the 56 day RP.

The?Clear Button – clicking this will remove ALL entries into the sheet (From Rank through to all the duties and Positioning/Flight entries – and There’s No UNDO!

[Read more…]

General Use Allowance Calculator

I have recently been looking at the allowances paid down route to us in LAX, with a view to developing and easy way to identify a discrepancy in what we should be paid; and to re-calculate what the difference should be in the event of an early arrival or delayed departure. Accordingly, I have developed this spreadsheet to be used for this purpose.

Note that you can run this sheet on MS Excel for iPad (as well as PC/mac, etc) although the “Clear” and “Sort” buttons won’t work on IOS.

When complete, the sheet looks like the image below. The blue sections are where the user enters information. The port is entered at the top (currently supporting BNE/LAX/MEL/SYD) and you can compare scheduled with actual to see changes in the allowances.

Note …

  • The On Blocks Date/Time (arrival) and Off Blocks Date/Time (departure) values must be entered in the same time zone so a meaningful total days/hours value can be calculated.
  • While the ATO pays a per day allowance based on meals/incidentals (so if you go 1 minute into a day, you get the full days allowance) the company only pays meal windows and incidental hours actually you touch with your off duty down route time.
  • Note that early arrivals and therefore early sign off’s should generate additional allowances (where relevant).
  • Delayed departures that do not result in delayed sign on do not incur additional allowances – you need to have your return sector sign on delayed to achieve additional allowances.
  • While the CSP’s (A1) specify 80 minutes between Sign On and Off Blocks for all international departures (from Oz and elsewhere); the company has increased this to 90 minutes for LAX departures.
  • The values in the current sheet are relevant for Pilots under the current EBA; Cabin Crew will need to amend the values in the data sheet.


There is a second data sheet you can use to update/amend the values the sheet uses to calculate:


EBA Allowance Calculator (Domestic Only) UPDATE

I recently developed a spreadsheet to check the domestic allowances I was being paid. The process was educational, to say the least. This initial version only checks domestic allowances – I will develop further to facilitate the checking of rostered vs actual international allowances as well.

Update : Recently Payroll have been paying correctly the meal allowances; but still persist on under paying the incidental allowance. I’ve also discovered they are unable to backpay correctly based on what was agreed was in error (hence V1.4 to allow you to enter backpay and highlight further discrepancies).

  • Version 1.4 (02Apr16) : Added a column on the RHS of the calculator to allow backpaid allowances to be entered and checked.
  • Version 1.3 (10Jul15) : Added allowances for post 01Jul15 (to be updated); unlocked the green allowances section for user edit.
  • Version 1.2 (14-Apr-15) : Bugfix Release (Dinner using Lunch Allowance in Duty Periods sheet).
  • Version 1.1 (05.Apr.15) : Initial Issue


Having only recently come to the EBA, I’ve started seeing the additional payments that come into my salary associated with Overtime, Callout and Allowances. The first of these two I track and check using my EBA Overtime Calculator, which you can get from the linked post. Certainly the comparison of what I believe I should be paid as compared with what I have been paid has been an educational process, illuminating for me both the detail of the EBA and inner working of the rostering and payroll systems, occasionally requiring follow up redress. I encourage everyone to check their overtime/callout when it’s paid every 8 weeks.

Allowances however are a different story. The process of calculating how much should be paid across a series of meal windows and an associated incidental period is relatively simple and I used such a process extensively in my Crew Allowance Tax Calculator (the latest of which can be downloaded from the link).

As such I figured it would be easy to develop a sheet to check my domestic allowances. To make sure I was doing it right, I started with the EBA, which is where I struck my first problem. The paucity of detail in this document covering a moderately complicated issue such as crew allowances at domestic and international ports was manifestly inadequate for my purposes. I fired off a couple of emails with comprehensive questions to the responsible line management, so far without a reply. In the end I reverted to the Short Haul EBA for the basis of calculation, the premise of which is basically that from the time you sign on at home Base for the purpose of operating Duty(ies) which include an overnight away from home base, you’re continuously paid Meal/Incidental Allowances until you sign off again back at home Base. This happens irrespective of whether meals are provided associated with your duties or not – or so my fellow domestic pilots advise.

I would like to give credit here to Dean Young, who provided the original formulae for the Allowance Checker. He was looking at this issue at the time as I was, and developed the formulae to assess the presence of a duty period over a meal window.

Dean was using a spreadsheet to fact check paid allowances, I used it for a different purpose (Tax) but the formula requirement was the same. His solution was elegant and with his permission I used it in my own sheet. Dean was responsible for much behind the scenes work in the early days of V Australia (we didn’t call it Volunteer Australia for nothing …), for which many will never appreciate.

Thanks Dean.

In any case I thought I had a handle on it so I started a sheet based on my Tax Calculator. It took me an afternoon to get a sheet I was happy with, which looked substantially like the following:


As always with my spreadsheets, the green cells are where you enter your information, the other cells are where you shouldn’t change things unless you want the calculations to go wrong. The Clear button deletes your entries in the green cells.

Basically you enter the periods away from home in green. On the 15th March I reported at 15:55 for a flight to BNE, to undertake a few days of simulator training, before returning to Melbourne, signing off at 18:50 on the 17th March after the flight home. The calculation is relatively simple where Incidental is purely based on hours away from home at a fixed rate; Breakfast, Lunch and Dinner meal allowances paid when your time away from Base touches any of the allocated meal windows. Or so I thought.

Allowance2However when it comes to checking the allowance you were paid – it’s a different story.

You see we are paid on a two week basis, covering a two week period, and we receive that pay about 4 working days after the close of that two week window. This payroll fortnight takes no account of your comings and goings and as such you can be paid for half of your time away in one pay check, and the rest of your time away in the next.

As such I was now confronted with the requirement to turn the fairly easy to enter blocks of time away from home base to a meal/date specific result that would be easy to check against the payslip. After much effort – I finally realised I couldn’t do it without code.

I therefore built a custom function in Visual Basic (Applications) for Excel, called:

Payslip (PaySlipDate As Date, Meal As String, Payrate As Currency) As Currency

This is certainly not my best piece of programming, it’s pretty quick and dirty, but it does the job. This formula requires three variables:

  • A Date – the date during the payslip period which is to be examined for possible allowances;
  • a Meal – the name of the meal band (“Breakfast”, “Lunch”, “Dinner”) which the calculation is to look for; and
  • a Rate – the rate of the particular meal allowance to be paid.

The value returned is either Zero (no allowance paid); in the case of Brekky, Lunch or Dinner the PayRate of the particular allowance if there is one on the date requested; or in the case of Incidentals – how much is to be paid in the way of an Incidental amount for that date.

This formula is incorporated into another sheet that looks like this:


  • The Payslip Date is Entered/Selected at the top.
  • The Start/End date of the related period fill in at the top, and down the LHS of the calculating area
  • Based on these dates, each Meal Period (and Incidental) for each date is reviewed in the context of duty periods away from base entered previously on the other sheet. If you were on station during a meal period on a particular date – this sheet detects that and fills in the amount. The incidental amount depends on how many hours you were away from Base (up to 24) and calculates it accordingly.
  • Once the sheet has calculated where you should have been paid something – the green cell next to the required payment value turns yellow.
  • The yellow cells are where you are required to enter something (one of the following):
    • Yes : You were paid the full amount. (enter the word “Yes”)
    • No : You were paid nothing against this meal/incidental allowance (enter the word “No”); or
    • $##.## : The amount you were paid (this is reserved for the Incidental figure as printed on your payslip).

The result?


As can be shown here, there is a missing meal, and the incidentals are rarely paid in full. From a review of the last 6 months of allowances calculated vs paid:

  • No incidentals are being paid on the first day of a duty (neither positioning up to BNE for simulator nor positioning up the day prior to simulator)
  • Incidentals are never paid in full for full days away from Base (my suspicion is that when I sign on to teach simulator in BNE, I stop being paid the incidental allowance).
  • The odd occasional meal drops out of the Company’s calculation. I originally postulated that when I signed on to teach Simulator, I was no longer being paid a meal allowance, hence the odd meal on most days there would be a meal allowance missing. However this turns out not to be the case – I can’t see any rhyme or reason as to why I’m missing a meal every now and then. Perhaps they’re not paying me when I skip meals?

Over the past 6 months the difference I’ve calculated comes to over $600. I have yet to claims these and will be doing so early next week. Many years ago I detected an error in the way I was being paid an allowance at Emirates, my previous employer. This error affected a small number of pilots several times a week (depending on them operating a particular flight pairing); but went back a couple of years. The solution was for the company to change the wording of our “contracts” so that the manner in which the allowance had previously been paid was correct. I don’t think that’s going to happen here .. but it will no doubt be interesting, especially given the vague wording of our agreement.

LNAV for a Localizer Approach

LLZ1I was recently asked whether we could still use LNAV to fly a Localizer Instrument Approach, and whether that was the preferred mode. This question was asked during a briefing on PBN which has caused some confusion.

Recently we’ve seen some changes in the way we do aircraft Navigation, or at least in the way we regulate it. PBN (Position Based Navigation) is here and exists in parallel with our existing Primary Means Navigation approval. We’ve moved away from the archaic limitations and practices of the specifics of manually and/or automatically referenced individual means of navigation sources and instead benefit from a system that encompasess and accounts for the limitations of all the individual available equipment and provides the best navigation information possible at any time.

Or we’ve just finally embraced GPS. It depends on how you look at it.

LNAV for Localizer Approaches

Localizer approaches are something of an oddity as far as they go. Basically it’s half a conventional ILS approach, where the glide slope (vertical path) component has failed, but we can still fly the approach using the Localizer (lateral path) albeit to higher minima and visibility requirements.

LLZ3Officially classed as an NPA – at the same time a localizer approach meets the recency need for an ILS precision approach (CAO 40.2.1-11.4); meanwhile our GPS Primary Instrument specifically excludes LLZ approaches (A1 15.5); even as PBN procedures make no reference. Finally the 777 Airplane Flight Manual references the (non) use of the FMC for the purposes of a Localizer Approach, but this is actually miss-leading …

CAO 40.2.1 Instrument Ratings
11. Recent experience requirements
11.4 The holder of a command instrument rating shall not carry out an ILS or LLZ approach in IMC as pilot in command of an aircraft unless, within the preceding 35 days, that person has performed in flight, or in a synthetic flight trainer approved for the purpose, either one of those approaches.

B777 AFM; Normal Procedures; Flight Management Computer System (FMCS)
The FMCS has been shown to meet the requirements of FAA AC 20-130A for a multi-sensor area navigation system when operated with radio or Global Position System (GPS) updating. When operated in this configuration, the FMCS may be used for enroute, terminal area operations and instrument approach navigation (excluding ILS, LOC, LOC-BC, LDA, SDF, and MLS approach procedures). The FMCS may be used to fly a RNAV approach procedure that overlays an ILS, LOC, LOC-BC, LDA, SDF, or MLS approach procedure when the localizer facility is inoperative subject to appropriate operational considerations, procedures, constraints, and authorizations.

CASA Instrument 187/13 GNSS Primary Means Navigation
4. Application
This instrument applies to the conduct of NPA procedures (excluding LLZ approaches) by … in B777-300ER aircraft with an RNP-capable RNAV system.

So what’s going here? Cutting to the chase …

The use of LNAV on a Localiser approach is fine as long as you have a valid Localiser signal and you remain within tolerance. When you use LNAV for this, your means of maintaining the centreline of the approach is the GPS / FMC / LNAV. But the means of validating your location on the centreline must continue to be the Localizer signal itself.

Thus the use of LNAV on Localizer approaches is acceptable with the same constraints as the use of the Autopilot/Flight Director LOC mode on a localizer approach – the engaged mode must keep the aircraft within navigational tolerance (half scale localiser deflection in either mode) at all times. There is no reason why LNAV shouldn’t achieve this to the same (or better) level of accuracy as the localizer signal; and both modes demand similar levels of situational awareness from the crew to ensure this. As long as you are monitoring the localizer on approach (and not just the flight director) – LNAV is a good choice.

As an aside – I like the use of LNAV to intercept the localizer for any ILS based approach, particularly when an overshoot (as scheduled by LOC capture) could infringe the approach of a parallel runway. However this does demand a higher level of SA from the crew than APP mode, since it delays arming glideslope capture until LNAV has sorted out the turn to final.

FMC Scratchpad Messages

There has been some discussion recently around FMC scratchpad messages, their role in flight deck alerting, and an appropriate crew response. Most particularly around the habit that some crew develop – usually during transition simulator training when many spurious messages are generated and often cleared without real understanding of their meaning). We areseeing this in the sim and in the aircraft – occaisionally to the detriment of the operation of the aircraft.

FMC (Flight Management Computer) scratchpad messages are generated at the bottom of the screen built into the FMC CDU (Computer Display Unit). It is a one line display that the FMC uses in order to pass a message onto the crew. They are not (directly) a part of Boeing’s design intent for the alerting system of the aircraft – that said, some of them do come with an EICAS alert FMC MESSAGE – many do not though.

The scratchpad itself is the incongruous name given to the bottom line of the CDU. Any text entered in via the keyboard or line selected down from the higher lines of the CDU end up in the scratchpad. From here they can be either cleared or line selected up into one of the lines of the CDU display above. As an example, you can use the keyboard to enter the name of a waypoint “YOW” and enter it into the LEGS page to change aircraft navigation.

The scratchpad is also where the FMC places messages. These messages cover many purposes – data entry errors; a requirement for additional information; details of uplink/downlink COM status, and more. Apart from the messages themselves, the FMC CDU also has CDU Annunciator lights on the front used to communicate as well (DSPY – Display; OFST – Offset; MSG – Message; and EXEC – Execute) – do you know (exactly) what they all mean?

Scratchpad messages are classified as follows, and come with the following annunciations:

  • FMS Alerting Messages (Scratchpad Message, EICAS FMC MESSAGE alert; CDU MSG light)
  • FMC Communication Messages (Scratchpad Message, EICAS COM Message (FMC) annunciation; CDU MSG light; Aural High-Low Chime)
  • FMS Advisory Messages (Scratchpad Message, CDU MSG light)
  • FMS Entry Error Messages (Scratchpad Message; CDU MSG light)

The use of the same space for data entry and to communicate messages would seem to be somewhat fraught – but not when you realise that there are actually two display lines in this area, one over the other, with the scratchpad data entry line having priority over the scratchpad message line. It is this feature that allows you to retain a scratchpad message while you correct the situation that prompted it – which is in keeping with the way we are trained to deal with most error messages on the flight deck. For example …

You were/are off track (due weather) and now that you are in the clear, decide to head back towards track and return to FMC LNAV navigation. You turn the track bug and the aircraft follows. You’re pointing towards the next waypoint, and select LNAV on the MCP. At this point LNAV appears in white on the FMA indicating that LNAV mode engagement is armed; but an FMC scratchpad message annunciates “NOT ON INTERCEPT HEADING“. According to the FMC Pilots Guide “LNAV is selected on the MCP and the airplane is not within the capture criteria of the active leg, or the current heading does not intercept the active leg.

The most common response to this is to clear the scrathpad message and adjust the track of the aircraft so that it intercepts the active leg. However if instead the message was left in the scratchpad, while you turn the aircraft to intercept the active leg, the FMC would re-evaluate the intercept and remove the message by itself – validating the action of the Pilot Flying. From a CRM/NTS/Error Management point of view – this is a far more satisfying solution.

But wait, there’s more …

I mentioned that in fact there are two scratchpads – and there are. It is possible to interact with the CDU scratchpad, either entering data via the keypad or line selecting data down from the CDU screen into the scratchpad, while retaining the scratchpad message in memory. Any use of the scratchpad by the pilot will hide the message, but retain it (if it’s not cleared first). Once you have used the scratchpad and cleared it of your entries – the scratchpad message will be displayed.

Note that although it may seem clumsy, it’s impossible line select a scratchpad message into a CDU LSK position – but still, it seems like a lot of bother, doesn’t it.

But consider the case of a runway change on departure. A new runway is selected and the FMC generates “TAKEOFF SPEEDS DELETED”. It’s telling you something important – “New performance data is entered after the VSPEEDS have been entered on the TAKEOFF REF page, a takeoff thrust selection change is entered after the VSPEEDS have been entered, or pilot-entered values do not comply with the relative takeoff speed check. The crew must reselect proper VSPEEDS.”

Normally the pilot manipulating the FMC will clear this message (hopefully with the acknowledgement of the other pilot) and then ideally deal with the missing speeds straight away. However it is entirely possible to retain this message right through a takeoff speeds entry process until the speeds are re-entered, at which point the message will self clear. Which of these two process is less prone to error – less prone to forgetting to re-enter your speeds?

In any event, our discussions did resolve one thing – we are going to introduce an SOP whereby a pilot who intends to clear a scratchpad message is required to confirm that action with the other pilot. For the most part – this should be happening anyway, but taking this action raises the visibility of a good habit – and give Check Captains something to look for as well.

Practices & Techniques : The FMC is trying to tell you something – why aren’t you listening?

The CDU scratch pad is the FMC’s prime method of trying to tell you something. Messages like “UNABLE HOLD AIRSPACE” or “TAKEOFF SPEEDS DELETED” or “ROUTE DISCONTINUITY” are the FMC’s way of communicating a problem to the crew – a problem that is valid, even if the crew don’t understand the message. It’s not uncommon to see crew clear those messages with minimal acknowledgement, a habit that unfortunately commences during simulator training.

CDU Scratchpad messages need to be dealt with like any other annunciation in the flight deck. Noticed, Called, Analysed, Acted Upon. Some of the more common(ly ignored) FMC messages are listed here.

VAI SOP Standard Calls require the CM1/CM2/PF/PM to confirm a scratchpad message with the other pilot prior to clearing a message. This requirement commences once the pre-flight initial CM2 setup / CM1 cross check is complete.

While there are scratchpad messages which are all but inconsequential to flight (STANDBY ONE or INVALID ENTRY) and there are messages which are commonly understood and occur routinely (INSUFFICIENT FUEL [during route changes]; UNABLE HOLD AIRSPACE; DRAG REQUIRED or UNABLE RTA) there are also messages which can have a significant impact of flight path and flight safety (DISCONTIUITY; INSUFFICIENT FUEL; RW/ILS FREQ/CRS ERROR; or TAKEOFF SPEEDS DELETED).

Finally, a smart pilot may not choose to clear an FMC CDU Scratchpad Message – but instead retain the message in the scratchpad until the underlying cause has been corrected. The CDU is fully functional while a scratchpad message is displayed with any data entered into the scratchpad line replacing the message until that data is either line selected into the CDU or cleared, at which point the message is returned – if it’s still valid. An example of this could include “NOT ON INTERCEPT HEADING” when LNAV has been armed but the aircraft is not tracking towards an active leg – correcting the aircraft track will clear the scratchpad message.

Standard Calls : FMC Scratchpad Messages

The FMC CDU communicates with pilots through data entered and calculation results on the CDU itself, four CDU Annunciators (DSPY, OFST, MSG and EXEC) and CDU Scratchpad Messages. These messages are categorised into Alerting, Communication, Advisory and Entry Error messages.

Anytime a CDU scratchpad message is generated after the initial pre-flight CM1/CM2 data entry/cross check procedure is complete – the CM1/CM2/PM/PF is required to check awareness in the other pilot prior to clearing the message. This is required whether the EICAS FMS MESSAGE is generated or not.


For a conservative NTS operation – consideration should be given to not clearing certain scratchpad messages, but instead dealing with the underlying cause behind the messages. Once the cause has been dealt with, the scratchpad message will be removed by the system. D5 Practices and Techniques refers.