When I arrived at V Australia in 2008 I discovered that what was missing was the institutional knowledge that an established airline develops over time, but never writes down … so I did. Eventually it became the SOP Guide : Practices & Techniques document. This blog series documents the continual growth of this training resource.

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Background

Recently I was in the simulator with two other instructors. One was my First Officer, the other was the Sadist … ahem … Sim Instructor. We were running without the ECL (paper QRH for NM and NNM) and the APU was failed. Climbing through about 5000ft, Los Angeles for Sydney – we received [] ELEC BUS L on the EICAS – the loss of the Left Electric Bus. Fortunately I was flying and so my long suffering FO was forced to deal with not only this failure, but all the consequent failures, through the paper QRH.

Although reference to a few paper checklists are involved – when you look at the checklist – it’s a no brainer really. You try a few resets, see if the APU fixes the problem, but in the end without the ability to restore the left electrical bus, you’ve lost … Window Heat (Left) and a Primary Hydraulic Pump (Left).

“That’s It?” my fly-buddy observed. I advised him to look at the roof.

Of course with the loss of one of the two main electrical busses in a modern (fly by wire) aircraft – there are a whole host of ancillary services lost. Many of these are reflected by the amber lights on the overhead panel.

Having looked at the roof – you later discover even then that it’s not the whole story. In this particular scenario we decided to return to KLAX. Part of the return process was fuel jettison down to maximum landing weight. Guess what? Without the Left Bus – the main tank jettison pumps are failed. You’ll be advised of this … when you start the fuel jettison.

I didn’t give this a second thought (I think I’ve been stuck on the same aircraft for too long) but it was interesting the discussion we had afterwards about this little quirk of the Boeing EICAS/ECL.  There are no EICAS/STATUS messages to advise you of everything you’ve lost, and in many cases until you attempt to use something that’s failed – you won’t know about it. Older aircraft used to publish a Bus Distribution List (Electrical and Hydraulic) so that you’d know exactly what you’d lost with a particular electrical bus failure – but not on the 777. My fellow pilots were vaguely disturbed by the lack of information.

We discussed it. Our decision to return was primarily based on passenger comfort. The entire aircraft had lost galley power, IFE and other passenger services and we decided it was unrealistic to continue 14 hours to Sydney without them. Would knowing that we weren’t going to be able to complete a fuel jettison have affected this decision … no.

We came up with scenarios where knowing fuel jettison was compromised would lead to a different diversion airport, but in the main they were pretty far fetched. In most cases it would have resulted in diverting to that other airport anyway using some of the fuel we were unable to jettison.

It’s an interesting system design/human thought process discussion. It’s one of those cases where you presume that the manufacturer has gone to great lengths to ensure the Need To Know list is complete and correct, and accounts for all the possible permutations of the operational environment.

And you hope your presumption is correct …

Practices & Techniques : 5.40 You Can’t Always Get What You Want.

The past two months have been flat out as I hit the ground running in the Fleet Training Manager role at the now renamed Virgin Australia International airline. As such Infinidim has pretty much taken a back seat, unfortunately. However in the New Year I plan to return to working on articles for Infinidim. There are several new items to write about for Practices and techniques, including a look at Missed Approach Acceleration, Navigation Systems/Situational Awareness and I can see an article coming on the use of FLCH for capturing the Glideslope from above.

Enjoy Santa’s Checkflight – In the meantime … have a Merry – Safe – Christmas.

Sometimes something as simple in the aircraft as looking and assessing the indications in front of you can be far more complex that it first seems. I was reminded of this in the simulator recently as several crews were required to assess aircraft pressurisation performance during a door unlocked indication failure in flight. First, some background.

Our current phase training includes a DOOR FWD CARGO unlocked indication shortly after takeoff. Apart from satisfying a matrix requirement and giving crew experience of this non-normal, the overt intent of this failure in the simulator profile is to give crew a reason to divert to the nearest suitable airport.

The DOOR FWD CARGO checklist itself requires that the aircraft be de-pressurised to ensure that if the door was to come off, less damage would be done than if the aircraft were fully pressurised. At this point the crew are at 8,000 ft and de-pressurised. Continuing to Los Angeles seems unlikely.

That said in a previous simulator we had two similar failures like this. The first was Door Forward Cargo indicating not locked in flight; the second was Door Forward Cargo – door comes off the fuselage out into the airflow and on it’s way down the side of the aircraft, takes out the right engine along with two hydraulic systems. As the instructor it was easy to confuse the two failures in the IOS – well, it was easy to confuse them once. Being pressurised/unpressurised never seemed to make much impact on the amount of damage that forward cargo door did as it embedded itself in the right engine – but I digress.

Anyway – so I was supposed to program a Door Forward Cargo indication failure on takeoff. I did this through the gear lever so I wouldn’t have to hit the button on the failure myself. I programmed the simulator so that when the lever was selected UP, the failure became active.

At least that was my intention – so far it hasn’t been successful. The Sim Instructor Operator Station (IOS) indicated the failure was active – but there was no indication to the crew, even after the takeoff inhibit ended. Oops. As it turned out later – this failure is only written by CAE to work on the ground. We’re still trying to find out why, but even knowing that isn’t going to change the fact that the failure doesn’t work airborne.

As such I was forced to improvise on the spot – often not a great recipe for training fidelity …

Sticking with the theme – I failed one of the other cargo doors instead. The problem now is that the simulator is VH-VPD which was our first owned aircraft, and it has the small version of the main cargo door aft of the wing. The size distinction is important in this failure. All doors on the aircraft (Cargo, Cabin, E/E Bay, etc) are “Plug” type doors – a Boeing innovation where essentially the door is bigger than the hole it fills and therefore the higher the pressurisation differential between inside/outside the aircraft, the less likely the door will come open. Don’t ask me how a door that’s bigger than the hole opens outwards to let the passengers and cargo in – that’s magic as far as I’m concerned.

Despite being a plug type door, when not indicating locked the Forward Cargo Door checklist requires the aircraft de-pressurise. We have always presumed this is related to the size of the door. The smaller Aft Cargo door does not require de-pressurisation and diversion – as long as the cabin is pressurising normally. Thus despite the failure the crew would assess and continue on to Los Angeles, extending the sim session from 2 hours to 14. Since I needed them to divert (no coffee or toilet in the sim) the next obvious choice was … you guessed it, pressurisation failure.

Because I knew the small door failure wouldn’t cut it, I programmed them simultaneously. Rather than the instantaneous heart-rate-raising big bang failure, I used slow de-pressurisation. Essentially the aircraft would fail to pressurise because the aforementioned small door was not only unlocked, but not properly closed. Hence the crew would assess pressurisation, realise the problem, and return. At least, that was the plan.

This statement seems pretty clear, doesn’t it?

Note: The aft lower cargo door is in a safe configuration 
as long as cabin pressurization is normal. Positive cabin
differential pressure ensures the door stays in place.

That shouldn’t be too hard to work out, should it? Pressurisation at this point is assessed via the AIR Synoptic page. Apart from showing good bleed air from the engines to the air-conditioning packs, the AIR synoptic also shows values such as Cabin Altitude and Rate of Climb, Differential Pressure and Forwad/Aft Outflow value positions.

A good crew would typically see the picture shown here during climb after takeoff. By “good” I mean a crew who would initially see the failure, think about it, then ignore it. They’d have QRH familiarity and know that this checklist doesn’t come with memory items, but they’d also know what the most likely outcome of this checklist was. They’d follow Boeing doctrine and delay running it until the critical take off phase was over, the aircraft was clean (gear and flaps retracted) and usually wait until the aircraft had cleared any terrain issues associated with the departure airport. Thus typically the aircraft would be climbing through about 7,000 ft by the time they finished the checklist and had a look at the AIR synoptic to assess pressurisation.

A quick glance shows you – Cabin Altitude below aircraft (as it should be); Cabin Altitude Rate climbing (normal, so is the aircraft); Outflow Valves Closed; duct pressure adequate, differential pressure positive. The problem here is … the quick glance. Like me – you’re looking to confirm the normal, rather than seeking what’s abnormal and looking for indications against the normal bias – looking to confirm a problem. Now let’s look again.

• Cabin Altitude – 5,500 is quite high. The cabin altitude is controlled in part by the selected cruise altitude. High takeoff weights (and therefore lower initial crusing altitudes) combined with the high cabin differential pressure capability of the 777 (9+ PSI), initial cabin altitudes in the 3000-4000 feet range are normal. This one is at 5,500 because the door is slightly ajar and the pressurisation system is unable to maintain the required lower altitude as the aircraft is climbing. It’s doing it’s best – I’ve been seeing cabin altitudes up to 2000 ft below the aircraft in the climb with this failure – but still to high for an initial cabin altitude.
• Cabin Rate – 800 fpm is not extreme, but again given the high diff of the 777 and the typically lower initial cruise altitudes, you see less than this typically.
• Cabin Differential Pressure – a Delta P of 1.2 is way too low. In cruise it would be well over 8. The 1.2 here is because the hole in the aircraft is not quite big enough to equalise the pressure – the Bleed Air/Packs are working hard. But 1.2 is far too low for this altitude when the pressurisation is working “normally”. Speaking of holes in the aircraft …
• Outflow Valves – The basic operating premise of an aircraft pressurisation system is that air flows in at a faster rate than it flows out – but it does flow out. It is only during Non-Normal events that you see fully closed outflow valves. Closed outflow valves are an indication that the Bleed Air/Packs are unable to provide adequate airflow – a pressurisation problem.

It’s very easy as the instructor to sit at the back and judge the errors of your students in front of you. It’s slightly more difficult to divorce yourself from the insider knowledge you have as an instructor and assess realistically. In this case, the signs are subtle – but they’re there. I could certainly not state with my hand over my heart that confronted with the same situation the first time, I would have picked up on these indications. For me though, the outflow valves are definitive. The only time they’re closed airborne is when something is wrong.

The discussion point here is the concept of assessing a system on the aircraft. With EICAS Warning/Caution/Alert messages – we are no longer used to looking at gauges and indicators and assessing the performance of a system. We are also separated from the normal operation of the aircraft by automatics and self monitoring systems and synoptics pages that were looked at during initial training, but now remain hidden away until they’re required by an unusual situation. We’ve become quite reliant on the alerting system to diagnose failures and provide clear, simple indications of what the problem is and what we have to do next.

So far most crew have missed the pressurisation problem that I programmed in concert with the door failure. Once the aircraft climbs above 10,000 ft (and the cabin above 8,000 ft) the pressurisation failure becomes clear and the crew act accordingly. For myself, serendipitously this experience has taught me to take simple checklist words such as “cabin pressurisation is normal” more carefully.

This week I’ve been working through a year’s (badly) stored paperwork as I (belatedly) prepare my tax return for submission to my accountant – who is traditionally a more onerous task master than the ATO.

As such I’ve hit yet another bug in the Allowance Calculator Spreadsheet. This one was on the Summary Sheet, Cell F7 and it was a simple subtraction – From the ATO Alowance take away the total Company Allowances paid for a Difference. Only I was referring to the wrong cell and so Cash Paid allowances weren’t being … allowed for. \

Fixed in this release – Version 1.7

I’ve recently been contacted by a friend from a previous airline who now works for another Middle Eastern carrier, flying 777′s. Interestingly enough – he’s chasing down information on Missed Approach Acceleration – an issue I also encountered when I arrived here at V in 2008.

Essentially at that time the initial training for the 777 Type Rating was provided in our own 777 Flight Simulator by Alteon, which is now a Boeing Company. While the contract required that our in house developed SOPs (based primarily on Boeing FCOM/FCTM documentation) were to be taught to our transitioning pilots – we encountered a number of stumbling blocks. One of these was Missed Approach Acceleration.

Background

At the bottom of an instrument approach, if visual reference is not established the crew are required to execute the Go-Around procedure and commence a Missed Approach. Initially configured for landing – the undercarriage is raised and some of the landing flap is retracted in the go-around procedure as the aircraft transitions from the descent to a climb.

This is the beginning of the Missed Approach Procedure. While the procedure may involve lateral manoeuvring (turns) – what I’m primarily concerned with here is the vertical component.

From an initial climb speed of essentially the final approach speed, at some point the aircraft will need to accelerate, retract flap and reduce thrust from a the go around (typically maximum) thrust setting to something like Climb/Max Continuous and establish level flight at a safe altitude. The bone of contention is when that acceleration phase commences. When I arrived, our students we being taught to accelerate at 1000 ft AAL in the missed approach, in common with the take off profile.

However a missed approach often does not follow the same departure track as a take off, and while intermediate acceleration for engine out departure profiles is assessed – this is not the case for engine out missed approach climb.

Boeing References

There area  number of Boeing FCOM and FCTM references in this area.

FCOM NP 21.40 “Go-Around and Missed Approach Procedure”

The FCOM normal procedures reference specifies acceleration at “acceleration height”.  This term is not defined elsewhere in the FCOM or FCTM.

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FCTM 5.64 “Go-Around and Missed Approach – All Approaches”

The go-around profile diagram in the FCTM again refers to “Acceleration height” without further defining this term.

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FCTM 5.58 “Go-Around and Missed Approach – All Engines Operating”

This section covers in detail the acceleration and flap retraction segment of the missed approach in more detail.

Go-Around and Missed Approach – All Engines Operating

The minimum altitude for flap retraction during a normal takeoff is not normally applicable to a missed approach procedure. However, obstacles in the missed approach flight path must be taken into consideration. During training, use 1,000 feet AGL to initiate acceleration for flap retraction, as during the takeoff procedure.

If initial manoeuvring is required during the missed approach, do the missed approach procedure through gear up before initiating the turn. Delay further flap retraction until initial manoeuvring is complete and a safe altitude and appropriate speed are attained.

Command speed should not be increased until a safe altitude and acceleration height is attained. Accelerate to flap retraction speed by repositioning the command speed to the manoeuvre speed for the desired flap setting. Retract flaps on the normal flap/speed schedule. When the flaps are retracted to the desired position and the airspeed approaches manoeuvre speed, select FLCH or VNAV and ensure CLB thrust is set. Verify the airplane levels off at selected altitude and proper speed is maintained.

Acceleration subsequent to a Go-Around should not be commenced until:

The FCTM does not differentiate the acceleration and flap retraction stage of a go‑around for engine out operation. In fact the recommendation is that the same procedure is to be used. 

Go-Around and Missed Approach – One Engine Inoperative

The missed approach with an engine inoperative should be accomplished in the same manner as a normal missed approach except use flaps 5 for the go-around flap setting for a flaps 20 approach or use flaps 20 as the go-around flap setting for a flaps 25 or 30 approach. After TO/GA is engaged, the AFDS commands a speed that is normally between command speed and command speed + 15 knots. The rudder is automatically positioned by the TAC to compensate for differential thrust with minimal input required from the pilot. Select maximum continuous thrust when flaps are retracted to the desired flap setting.

This implies that acceleration and flap retraction during an engine out go-around:

• Should not be commenced until the same criteria has been met as for a normal go-around;
• That the same procedure is advisable for both All Engine and Engine Out manoeuvres;
• That 1000 ft AGL should be used during Training.

The Problem – Missed Approach Acceleration at 1000 ft AAL

This is the crux of our problem. Owing to the references in the FCTM to acceleration at 1000 ft AAL “During Training” – Boeing/Alteon teach their/our students that Missed Approach Acceleration (both All Engine and Engine Out) requires acceleration to be commenced at 1000 ft in the missed approach. This is actioned by increasing the speed on the MCP – and it’s wrong.

As we’ll see below – ICAO PANS OPS has no concept of acceleration and clean up in the middle of a missed approach. While it’s true that there is a concept of initial, intermediate and final missed approach segments, these refer to climb profile (initial missed approach finishes as the aircraft reaches positive climb in the missed approach manoeuvre) and terrain clearance – there’s an increased terrain clearance requirement in the final missed approach segment.

The primary reference document here for us is the ICAO document 8168-OPS/611 (volumes 1 and 2).

PANS OPS Missed Approach Procedure Acceleration

An instrument approach requires a maximum nominal gradient of 2.5% from the commencement of the intermediate missed approach segment, to the completion of the final missed approach segment.

Terrain at certain airports may require gradients in excess of this in which case this is documented on the relevant approach plate.

The missed approach path is segmented into Initial, Intermediate and Final – with associated limiting speeds (Cat D aircraft) of Intermediate 345 kph (186 knots) and Final 490 kph (264 Knots). The delimiter between the intermediate and final missed approach segments is the obstacle clearance achievable.

As such, while the speed limit associated with the missed approach construction should allow acceleration to Vref 30+80 after a go-around, the missed approach path construction itself does not include any allowance for an acceleration segment. This does not mean intermediate acceleration cannot be undertaken – but no terrain clearance allowance is made. The aircraft must clear 2.5% from the MAP (Missed Approach Point) to the MAA (Missed Approach Altitude).

As primarily a JAR-OPS airline, a detailed examination of the FAA United States Standard for Terminal Instrument Procedures (TERPS) documentation has not been completed for this issue. However it is know that an intermediate acceleration segment is not part of the American regulations, and minimum gradients of anywhere from 2.1% to 3.3% are in use, terrain notwithstanding.

Procedural Commonality – All Engine vs Engine Out

Because of the excess thrust available during a two engine missed approach, an intermediate acceleration segment could potentially be scheduled during a two engine missed approach and still allow the aircraft to remain clear of terrain. However this would mean documenting, training and relying on the recall of two different procedures for the missed approach, depending on whether this is flown with one engine inoperative or not. Most airlines reach the conclusion that this carries an unacceptable safety risk against an acceptable loss of potential engine wear and tear and extra fuel usage for the relatively few two engine go-arounds that are encountered in normal line operations.

Many crew have enough difficulty scheduling a 1000 ft acceleration during an all engine missed approach, without having to remember not to do it during an engine out missed approach.

Engine Thrust Limits

Extending the missed approach segment to the MAA has the potential to infringe on the 5 minute limit on engine thrust in excess of Maximum Continuous Thrust (all engine) or the 10 minute limit on engine out thrust in excess of CON thrust.

However the risk of an exceedence of the 5 minute all engine limit is low, owing to the excess thrust available when two engines are operational. In any case, during a normal all engine missed approach a setting significantly less than TOGA thrust is scheduled (enough for 2000 fpm) unless required by the performance of the aircraft – in which case it’s … required.

Our crew are trained to be aware of these limitations and in the event of a 5 minute or 10 minute exceedence, manual selection of CON thrust is available to the crew through the CLB/CON switch on the MCP, terrain clearance permitting.

It should be noted that the 5 or 10 minute limit exceedence is likely only when a high MAA is involved. A high MAA is almost certainly the result of significant terrain in the missed approach path, which is exactly the situation where an intermediate acceleration and flap retraction would most put the aircraft at risk.

In Summary : SOP Missed Approach – All Engine & Engine Out

We train our crew using the standard Boeing FCOM NP’s, with an additional document (SOP Guide : NPs) to clarify interpretation and any procedural differences.

Both All Engine and Engine Out missed approaches are flown to the Missed Approach Altitude, without acceleration. PF/Capt may elect to accelerate early if above MSA and confident of remaining so to the completion of the Missed Approach flight path.

Crew are training in this procedure through documentation, in the simulator and during line training. Boeing/Alteon notwithstanding.

A while ago I wrote about issues we were having with inserting an arrival and approach into LAX prior to exiting Oceanic Airspace across the Pacific. Essentially during the 500 mile run into our exit point (such as ELKEY) our FANS system would send a CPDLC report every 12 minutes or so announcing to the world that the pilots on board the aircraft had been playing with the waypoints in the FMC after the exit point. Automated alarms and queries from ATC – and we’d have to remove our carefully built arrival until we were out of Oceanic Airspace and approaching descent into LA.

After a discussion with Oakland Oceanic while on the ground in LA, I worked out that the solution was to flight plan out by the two paired oceanic points, thus denying ATC the option of sneaking a peak at our flight plan after the last Oceanic waypoint.

Well, today we tried it and it wasn’t a problem. Our exit point was ELKEY and so Nav Services planned us via EDTOO->ELKEY->KLAX. I had the arrival and approach inserted and briefed shortly after I came back from rest with nary a peep from San Francisco.

One complication is that since we use effectively a random routing of lat/lon waypoints across the Pacific, and often don’t follow any of the established airways into the Oceanic exit waypoints, the additional waypoint may add a few track miles to our route. Nav Services has reviewed our most commonly used routes and decided on a standard set of paired waypoints for the exit. We should start seeing these paired waypoints on our flight plans, solving the problem of delayed FMC preparation for the arrival into LAX.

Crew need to understand the need behind these two paired waypoints, particularly in the event of a bit of a kink over the leader waypoint prior to the exit – and not ask for a direct to the Oceanic exit.

When I arrived at V Australia in 2008 I discovered that what was missing was the institutional knowledge that an established airline develops over time, but never writes down … so I did. Eventually it became the SOP Guide : Practices & Techniques document. This blog series documents the continual growth of this training resource.

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Background

Any long haul pilot is well aware that changes in the weight of the aircraft at takeoff have a significant impact on the fuel burn of the flight. This includes changes in Fuel as well as Payload. For example – If I decide that I want to carry an extra 2000 kg of fuel from Los Angeles to Sydney for holding purposes (which is less than 20 minutes or 4 holding patterns by the way), then apart from the holding fuel – I’ll need to load an extra 900 kg of fuel – to carry the extra 2 tons. As such – I’ll need to load almost 3000 kg of fuel in order to be able to carry out 4 holding patterns prior to approach into Sydney. Has anybody mentioned this to Sydney ATC?

The correction required is partly based on the weight concerned, partly based on the length of the flight. Our flight plans come with a correction figure to allow us to calculate the change in Fuel Burn that results from a change in Take Off Weight – assuming the weight is being carried to destination – it’s called the the LNDG correction figure. For example if the payload of the aircraft increases by 1500 kg and the LNDG correction figure is 500 Kg/Ton – I’ll have to add 750 kg to the refuelling figure to cover the increase payload. Note that this 750 kg not only covers the 1500 kg of weight – but the overall increased 2250 kg total weight of the aircraft. Confused? Read On.

Recently we’ve been having fun in Abu Dhabi with restricted take off weights due to the high ambient temperatures. This has necessitated some fast figuring on the backs of the flight plans as well as some quick SATCOM calls to Nav Services. And it has renewed my interest in a technique that our ex-Cathay pilots have shown us on how to use the OFP LNDG correction figure to calculate a new limiting ZFW based on a force TOW change.

Time to write it into the P&T.

Practices & Techniques : 8.25 Using LNDG To Calculate A Change in ZFW based on RAMP Weight Change.

After my recent debacle in Abu Dhabi – and another occurrence involving offload and a 4 hour delay- I was asked to prepare some specific advice for Captains operating out of Abu Dhabi.

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Abu Dhabi (OMAA/AUH) High Temperature Flight Operations.

Background

Green is our Departure Time. Yellow is Peak Temperature.

Due to high temperatures, most Abu Dhabi departures during mid Summer experience a potential performance penalty for departure; in most cases resulting in loss of revenue payload, possible departure delays due offload and in the severest of cases the offload of all Cargo, Standby Passengers/Bags and Revenue Passenger Bags to enable departure.

At this time of year the midday temperatures in OMAA are in the mid 40°’s. When contrasted with the average load carrying capability for our 777’s in these temperatures; and the high loads of passengers and freight departing Abu Dhabi during Summer – it’s clear that crew will be required to plan for a performance limitation on takeoff.

Note : The data provided here is for information only and not for operational use. Any statements of rules of thumb; values of temperatures and winds; preferred runway selections; performance limit weight changes due ambient conditions such as Temperature, Wind, Runway Selection, APU-PACK usage etc are informational only – all takeoff performance estimates must be verified and calculated by the crew in the actual operating environment of the day.

Considerations

Yellow areas are the likely Pax-Only Departures.

Effect of Temperature

From the charted data – it can be seen that increasing temperature has a significant impact on the load carrying capability of the aircraft. Once below the Certified Takeoff Weight, each degree increase reduces the takeoff performance limit by at least 3.0 Tons – often more.

Assuming a full load of passengers and crew – at planning temperatures of 40° and less, some revenue cargo can be carried for the departure.

However as the temperature increases, the performance limiting condition reaches a point where revenue cargo cannot be carried. In a highly subjective calculation – this is indicated by the yellow/bold sections of this sample chart. Your mileage may vary.

Effect of Wind

It can be seen that an increasing headwind component helps increase load carrying capacity by an average of 300 Kg/Knot. However this rule of thumb is far from reliable because there are points at which headwind helps with a specific performance limit and the increase in permitted takeoff weight is higher (900 Kg in some cases for 1 knot increase in wind). Crew must examine various contingencies of the wind before deciding on a planned set of departure conditions.

Departure Time

Our departure time of 11:00 am leads up towards the peak heat of the day. This has two operational impacts. Temperatures are high and therefore our capacity to fill the aircraft is compromised. Additionally any significant delay to the departure – such as to offload cargo/standby passengers in order to comply with a weight restriction – takes the aircraft into even higher operating temperatures. Once into this peak temperature regime (about 14:00 Local) it can be up to 4 hours after Scheduled ETD before temperatures reduce.

Sea Breeze

During the morning temperatures build and OMAA general experiences southerly (crosswind) to easterly (HWC RW 13) winds of up to 10 knots. That said – usually the breeze is less than 5 knots and of variable direction.

Between late morning and early afternoon a wind change is usually experienced (RW13 -> RW31) and winds of up to 10 knots can result. Once the sea breeze is established it’s normal for temperatures to commence a slow decrease through the rest of the afternoon.

If you can get it - and the wind doesn't kill the advantage - RW31L is preferred.

Choice of Runway

All runways in Abu Dhabi are of equal length and approximately equal slopes (actually  0.05% up to North/West). There are obstacles in the database off the end of all runways, and RW13 L&R have an EOP. It is this last factor which determines that generally RW31 gives better takeoff performance than RW13. However this advantage is generally less than 1 Ton and is quickly negated by wind.

APU to PACK

APU to PACK will generally provide a takeoff performance increase of about 3.5 Tons. Crew should familiarise themselves with the APU to PACK procedure from the FCOM SP during pre-flight; and consider reviewing the APU to PACK detail in the D5 OPT Guide prior to flight operations in Abu Dhabi.

APU To PACK in Abu Dhabi forces some additional operational considerations. Due to high on ground temperatures – with a full load the cabin temperature towards the back of the aircraft will be in the high twenties prior to engine start. As such the requirement to run two Packs out to the runway for passenger comfort is almost a certainty. Recommended technique is:

• Use conventional data entry procedures to enter all takeoff data as planned for the departure – even if you’re not sure those figures will be used for takeoff. Select APU in the Assumed Temperature line, verifying small font APU on the Upper EICAS.
• After engine start verify large font APU on Upper EICAS and Single Pack APU operation.
• If deemed necessary delete the APU entry in the Assumed Temperature line of the CDU THR LIM page and verify dual pack operation to the cabin. This action will delete the takeoff speeds from the FMC.
• Delay the Takeoff Review and Before Takeoff Checklist until final takeoff performance entries are complete
• Plan to position near the runway such that a short delay will be acceptable to ATC. When ready, perform the FMC Final Performance Entry procedure in full and re-enter takeoff performance data while the aircraft is halted with both operational crew involved as scripted.
• Complete Takeoff Review and the Before Takeoff Checklist when ready.
• If APU to Pack should fail – Turn the Packs OFF (refer to SP) nearing the runway (note 30 seconds minimum before thrust advancement) in place of APU to Pack.

Over Fuelling

When planned at 40° OAT – the flight can include 10-15 tons of cargo with a full load of passengers, based on a re-dispatched OFP fuel load. However if temperatures increase and a subsequent offload (or non-load) of Cargo is undertaken – even with 3 ton below refuelling the aircraft can be left with too much fuel to even depart with minimum passenger load.

If an over fuel situation develops, De-Fuelling is almost always NOT an option. One option to consider is pushback and taxi to hold near the runway – to wait for fuel reduction (minimum 2.0 tons per hour during taxi) or improved ambient conditions (post peak temperature, wind change, sea breeze).

Flight Planning

The Flight Plan will be prepared to a forecast temperature at the time of departure plus (based on recent operational experience) a margin. In all likelihood it will include some capacity for revenue freight.

If the flight is planned with Cargo, Captains should consider the following plan of action:

a)     Obtain an estimate of the ZFW required for Revenue Pax/Bags and Standby Pax/Bags from the AUH Ramp Dispatcher.
b)    Obtain a minimum fuel OFP from Nav Services for this ZFW.
c)     Refuel the aircraft to this minimum fuel (instead of originally planned OFP less 3 tons)

This will enable the crew to decide to Offload/Not Load Cargo (and potentially Standby Passengers/bags) – and be left with just the fuel required to complete the mission, giving the minimum takeoff weight available for departure and therefore the greatest margin to the performance limited takeoff weight. Although the correction figures could be considered to correct for freight offload – the magnitude of values involved are beyond the accuracy of the LAND/RAMP correction figures.

PushBack, Taxi, Departure – Performance Entry

Pre-Flight : can be characterised by finger-flying calculations on the OPT; multiple sources of ambient conditions (Tower, ATIS, Aircraft OAT); changing ambient conditions; different ZFW/TOW figures provided from different sources. Captains must proactively manage these conditions and decide early on a plan to minimise the risks associated. The integrity of the Final OPT Calculation and the Data Entry Procedure is paramount.

Decision Time : There may come a point where the Captain will have to make a decision on a ZFW that can be accepted based on a conservative use of the OPT and expected temperatures/conditions. The decision to take on cargo and the fuel to carry it must be balanced against the possibility of increasing temperatures that could force a cargo offload – and a delay into even higher ambient temperatures for the departure.

Performance Data Entry : Captains may well find themselves having to enter critical performance data during taxi. It is strongly suggested this should be done in full compliance of the Final FMC Pre-Flight entry procedure after a full cross check of the final OPT solution (from scratch) involving both operational crew members while the aircraft is halted near the departure runway. Takeoff Review and Before Takeoff Checklist is delayed until the completion of the Performance Entry Procedure.

Yes, Another bug found (thanks Sam) in the allowance calculator spreadsheet. The wrong date was entered on the first sheet for the column of Payslip Pay Dates. Current Release is now 1.6

Ken

Managing a departure with a performance limited takeoff weight can be one of the more challenging tasks that face an Airline Captain today. It all sounds simple enough in theory. Based on the Airport/Runway, Ambient Weather Conditions and Aircraft, a computer will spit out – down to the kilogram – how much weight you’re allowed to lift off the runway. From this number a passenger/cargo and fuel load is determined – and off you go. But all is not as it seems.

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Having been caught in the past, on the back of my clipboard is a little cheat sheet for the airfields we operate to, which gives me either

- the maximum weight I can expect to lift off an airport/runway in standard conditions (generally shorter runways); or
- the temperature above which I can expect to have to reduce below maximum certified takeoff weight (351,534 Kg in the 777-300ER).

This is certainly not an operational document – indeed it’s always out of date because I only update it infrequently – but it gives me an approximate idea long before I get to the plane as to what sort of limits I might encounter on the departure. A heads up, so to speak. And with temperatures in Abu Dhabi (OMAA) reaching into the 40′s – you can see where the problems begin.

Interestingly, in my previous airline, I rarely encountered performance limited takeoff’s – which could be considered a regular event at our home airfield of Dubai. The most common place for me personally was actually Melbourne (YMML/MEL) when a heavy departure combined with a light breeze from the north would leave you with  the poor man’s choice of a departure to the north into the wind over the climbing terrain – or a departure to the south over nice flat suburbs leading to the bay – with a tailwind.

Combine temperatures above 30 degrees with 10 knots from the north and with the fickleness of the wind, the optimum solution would flick back and forth between the two opposite runways. When the wind from the north was feeble enough (typically less than 10 knots) to embolden you for a tailwind departure to the south, often you’d sit at the holding point for 45 minutes waiting for a space in the traffic pattern before you could go – all but negating the advantage of the southerly departure. But I digress.

Briefing

Our little saga begins in Abu Dhabi (OMAA/AUH) on our fourth and last day in the UAE, at 9am. We have arrived early at Etihad briefing where we were usually provided with the flight plan and other documentation on arrival. We were a little early but even so the flight plan was already 30 minutes late with no indication as to when it would arrive. Several fruitless phone calls later I implemented the Paul McCartney solution to airline problem solving – I just Let It Be.

The plan eventually arrived and we noted that we were (unsurprisingly) performance limited for Takeoff. Instead of our certified 351.535 Tons – today’s takeoff was planned at 342.036 Tons, which included 122.5 tons of fuel – the minimum required to get the aircraft safety from Abu Dhabi back to Sydney.

Operations had thoughtfully provided the basis of their calculation:

Runway 13L; Temp 40; Wind Calm

I looked into my Android phone and found the current temp at OMAA airport was 36 degrees, and a ten knot headwind was blowing down the active runway. A departure 90 minutes from now at 40 degrees seemed conservative enough – we reviewed the documentation, briefed the crew and headed for the aircraft.

Apart from our departure threat – there were two jet streams to contend with – one a headwind that we were to cross just after entering the Sea of Oman; the second we would follow like a ski run across the Southern Indian Ocean and right across Australia. This 160 knot (300 kph) tailwind was responsible for our shorter flight time (12:30 hours) but could well bring some moderate or worse turbulence. Finally Sydney was forecasting passing showers with a cloud base as low as 800 ft. Nothing un-toward but since our dispatch was to be with minimum fuel, I was already considering way to increase our fuel load – nothing gives you more options like additional fuel.

At the Aircraft

V's first flight to AUH was full of celebration and hoopla. Ours, not quite so much ...

We arrived at the aircraft at about 60 minutes before departure. Traditionally I offer the Flight Management Computer setup to one of the Relief First Officers, but I realised time was going to be tight (how little I knew at that point) and we stuck to standard SOPs.

Gareth and I did our setup, Ben headed out into the sauna for the aircraft walk around, and Tian completed safety and security checks for us, as well as kick starting the laptops, pulling out the charts, preparing the flight docs and the dozen or so other jobs that our unsung relief crew perform on every flight to assist the primary crew in getting the plane moving.

Fairly soon after arriving on the flight deck, we were approached by the Dispatcher Misha – who wanted an increase in takeoff weight.

The weight dictated by Ops required her to offload an entire pallet of approximately 4 tons for a 900 kg overload. There’s generally no time to split pallets this close to departure so unless you can get the whole thing on, the whole thing has to come off. I told her it might be possible, but we’d not be able to confirm for 15 minutes or so.

With the takeoff on our minds and Misha’s request in our ears, we reviewed the latest ATIS and asked for current temp/wind from the Control Tower. Often the ATIS can be a little old and the Tower often has useful gen on the history and future of winds and temps – they see the same thing day after day after all, particularly somewhere highly predictable like Abu Dhabi. In this case – both of the latter two suppositions were incorrect. The ATIS was accurate and the Tower not particularly helpful.

The temperature was now 37 degrees and the wind 10 knots down the runway. We were approaching 40 minutes to departure and passenger boarding well underway. Gareth and I pooled our 20 years of Middle East experience and decided to plan on a temperature of 40 degrees and 5 knots of headwind, which felt conservative enough. This gave us an additional 3 tons to play with. Pushback time was 10:55 local and despite a long taxi to the far runway (closest runway closed) – we were confident it would be ok. We gave Misha her additional ton and ourselves an extra ton of fuel, leaving us a margin of a final ton under our hopefully conservative takeoff performance calculations. We then continued on with our preparations.

Final Zero Fuel Weight

As all airline pilots know – this is make or break it time. Load control (in our case, Misha the dispatcher) provide you with the final weight of the aircraft and based on this you determine your fuel load. Misha had increased the aircraft weight by 1.1 tons (cheeky) to which we added our extra ton of fuel – plus the 500 kg’s of fuel required to carry Misha’s extra ton. We checked the ATIS weather again – still 37 degrees and 1o knots of headwind – and Gareth and I separately calculated Zero Fuel Weight, Takeoff Weight, Landing Weight and Fuel At Destination – and then compared them to each other and the structural/performance limitations to ensure calculation accuracy and practical legality. Then we gave the relevant figures to Misha, advised the refueller of our final fuel requirement, and rolled on into the straight run towards pushback and departure. Pretty quickly the refueller completed our final fuel and disconnected the refuelling truck. We were almost ready to go.

This is when things started to wrong.

Typically up to this point you have refuelled to 3 tons below the fuel you’re expecting to need. That way if the final weight comes in under what’s expected – there’s often a variance like this – you can reduce your final fuel order and not carry extra fuel un-necessarily. Changes in weight have a significant impact on long haul flights – for our flight a decreased of the aircraft weight of 1000Kg reduces the requireed fuel by 450Kg. Given the price of fuel and the economics of operating an airline today – not carrying extraneous fuel is a significant impact on the economics of the operation when taken across all the flights operated by the airline.

Wind and Temperature

Over the next thirty minutes we watched as the wind dropped off to 5 knots with a variable direction such that we could not count on any head wind at all. The temperature meanwhile climbed from 37 degrees to 38, 39, 40 – and 41. In these conditions, every degree of temperature rise reduces the performance limited takeoff weight by anything from 1500-3000Kg. Each knot of wind loss reduces takeoff performance by approximately a 200 kg change. Ask me how I know this.

By the time the cargo and passengers were fully loaded, the paperwork ready to go and all but the last passenger and cargo door closed – we were now 8 tons overweight for takeoff. We reviewed our calculations, looked at alternate runways, did some what-if’s with the wind. We were already planning to run the air-conditioning off the auxiliary power unit (APU) to maximise thrust from the engines – there was literally nothing further we could do.

I found Misha and discussed the situation with her. We decided to commence offload of our freight. There were issues here – some of the freight was high priority, there were going to be balance problems. We had about 10 staff on board the aircraft who could also be offloaded. Thus the offload would be in three stages – Freight, High Priority Freight, Staff & Staff Bags (the last two not necessarily in that order).

While this kept Misha busy – Gareth, Ben, Tian and I now had to determine what conditions we were going to use for departure – and therefore what limiting weight was going to be imposed on the cargo load. As we struggled with our crystal ball each time we picked a scenario that seemed conservative, we were looking at offload a portion of our revenue passenger’s bags – and perhaps some of the passengers – to deal with the situation.

At one point Gareth looks at me and says “I’ll ask the tower what the maximum temperature will be today.” Right.

Despite the dizzying force of my subsequent withering gaze of disdain, eternal optimist that he is he jumped on the radio and asked Ground Control what the maximum temperature was going to be. “Forty Two Degrees, Insha’Allah, Captain.“, was the answer. It’s 41 outside at this point, and about 12pm local time.

Gareth looked at me encouragingly – 42 we can cope with.

I passed my hand across the flight deck through space and time and intoned the words “It will not go above 42 degrees.” After a lack of reaction from Gareth, I followed up with “The force gives power over weak minds, Luke.” Gareth’s turn for a withering gaze.

Let me finish off this little bit with a picture of OMAA Airport Temperatures for the day in question. That tall bar in the middle – that’s when we took off.

Too Much Fuel

I must point out here that our problem was not just the weight of the freight and passengers – but also the fuel. We had calculated a required fuel load based on Zero Fuel Weight ZFW (aircraft + load) of 219.6 Tons. We were now busy offloading cargo to achieve a ZFW of 209.1. Thus the fuel we required could similarly be dropped by about 6 tons – except that it was already on board the aircraft. If we got to the point where we’d offloaded the cargo and the anticipated conditions were such that we still could not take off – we would have to consider de-fuelling.

While the word “defuelling” seems a simple alteration of the more familiar “refuelling” the actual process is far from similar. Depending on AirlineSOPs, local conditions and the availability of equipment, de-fuelling can have the following characteristics:

- All passengers disembarked prior to de-fuelling commencement until completion;
- Separate truck specifically reserved for defuelling purposes (if available);
- Typically the truck does not have the facility to pump fuel off – the aircraft needs to do the pumping and generally manages about 125 kg / minute.
- The fuel cannot usually be used by another airline and must be kept for your airline the next time you refuel.
- Local variations apply.

To say the re-fueller/engineer was disenchanted with the concept of de-fuelling our aircraft was an understatement. He seemed a fairly taciturn individual right up to that point where I asked him about de-fuelling. From that point on he just kept smiling at me.

There are two ways to defuel. The first is into a truck. The second is to start the engines, taxi out and stop somewhere, burning fuel until you’re down to the required weight. During a taxi the engines burn fuel at about 2 tons per hour. If necessary you can increase thrust a little while holding the brakes and perhaps double that flow rate. Neither of these are great options – best choice is not to let yourself get trapped into the situation in the first place …

The Passengers

We hadn’t forgotten our passengers through all this. During the delay I made two Passenger Address’s explaining situation and updating as we went along; the crew and the entertainment system kept the passengers busy and satisfied as best could be achieved; at one point as we waited with nothing to do I walked through the cabin talking to passengers answering questions. There were issues with connections and certainly some disgruntled passengers but all told our Cabin Crew worked really hard on service recovery. I stood near the door after the end of the flight and for the most part got smiles from our glad to be in Sydney passengers.

The Staff Travel Passengers

In a situation like this, the aircraft loadsheet marks some the passengers as PAD – Passengers Available for Disembarkation. Essentially this is the staff of the airline, their families and friends who can be offloaded in order to preserve the dispatch of the flight, the existence of revenue passengers onboard, and various other reasons. Misha calculated out staff pax at 700kg on our flight including their bags. I knew that a decision time was coming and we discussed a possible offload of them. This would require finding those passengers – and their baggage strewn throughout the loading pallets in the hold. I decided that the time it would take to accomplish this was no more that the time it would take to burn off the equivalent fuel, and kept the staff on board. I was fully cognizant that I might come to regret that decision …

As an aside, I also considered offloading some water. The aircraft carries about 1.5 tons of potable water. Typically on a long full flight there’s almost a ton left. I’ve used this technique in the past to carry an additional passenger or two when we’ve had empty seats but we’ve been performance limited. Again in this case – it seemed more practical and less risk to burn the fuel on taxi. I may never be allowed to vote Green again.

Decision Time

As the cargo had come off – including some re-arranging of passenger baggage from the Aft to Forward hold for balance purposes – the temperature was increasing still. The wind was still reported as 5 knots variable, but also “Becoming” a 6 knot wind from the other direction. The sea breeze was kicking in, resulting in a Northerly that would force a change of runway (which didn’t help performance) but a potential increase in headwind component. We were now 90 minutes passed our scheduled departure time – it was 12:30 and we were still not at the peak heat of the day. Misha had confused us several times with a varying range of Zero Fuel Weights depending on what was offloaded and what was kept. I couldn’t blame her – we had flight plans and takeoff calculations flying around the flight deck like no man’s business.

Misha confirmed that at ZFW 209.1 we had all pax (staff and revenue) and their bags on board. No freight – including the high priority freight. Based on the amount of fuel still on board we were now – and depending on which set of imaginary numbers representing the temperature and wind we’d see at the runway – at least 1500 kg overweight still.

I decided we’d push back and taxi out. If the wind had not picked up producing a headwind, we would wait somewhere and burn off the ton of fuel. If the temperature increased, we would need to burn more.

Push Back

Of course nothing is that simple. Now that we were no longer a flight in quandry, but a flight trying to push back – the real world intrudes on our flight once again. There was a now disparity in the passenger numbers to sort out, paperwork to finish, a loadsheet to chase from Ops, a NOTOC to revise (no hazardous cargo onboard anymore), passengers to update (who for some reason would not take their seats) – and after two hours of a quiet, Abu Dhabi airport decides this was the time to ramp up activity. We sat on stand, fully ready to go for an additional 15 minutes waiting for push back.

Because of a runway closure – it was a long taxi out to our departure runway. As we finally pushed back and started engines, I could hear Ben behind me checking the ATIS airport weather. I snuck a glance back – Not good. No wind and the temperature was now 43 degrees. If it went to 44 without a wind shift we’d be parked by the runway for at least an hour, burning through fuel.

Another consideration was the APU to Pack takeoff. The procedure was designed to be enacted prior to pushback and once engines were started, one airconditioning pack would shut down and the other would run off the APU until after takeoff. Single Pack combined with our long taxi would result in a very warm cabin. Thus we would have to disable the APU to pack for a while and the re-engage it approaching the runway, re-entering our takeoff performance calculations as as we did so. Less than ideal.

But not such an obstacle really, since we were taxi-ing out with no clear idea of which runway we would depart from, what the temperature and wind would be, and how long it would be before we could go. Everything would need to be done at the holding point in the end. Hopes and dreams were all we had really.

Saved by the Wind

Approaching the intersection at which we would have to choose a runway – we contacted Tower for an update on winds and temps.

“Temperature? 43 Degrees Captain. Wind? 300/6, Runway 31R in use.”

The wind had now swung to favour the other runway. We’d checked figures for RW31R but it hadn’t helped quite enough. However the combination of runway and headwind was helping. We turned right and continued along the inner taxiway – leaving the outer for aircraft that actually could takeoff.

Once halted clear of the runway, we made the necessary aircraft and flight management computer changes for the new runway, updated the departure briefing, and asked again about the wind.

“Wind is 310/8 Captain. Temperature 43 degrees.”

Success – we calculated the figures and our limiting takeoff weight exactly matched our current aircraft weight. We expedited onto the runway and took off for Sydney.

Postscript

With all the additional fuel on board, we contact Ops and gained approval to increase speed and burn some of it – we had literally dozens and dozens of passengers with connections to all over Australia. We kept an eye on the weather in Sydney (which was a waste of time because it only degenerated to Rain Showers and a 600 ft cloud base once we’d commenced descent) and tore through time and space at Mach .855 most of the way (I’ve done Mach 86-88 on the 7773ER – but that requires a LOT of fuel, which even we didn’t have).

Having shaved perhaps 40 minutes off the flight time, we then held for 35 minutes on the descent (round and round and round) and flew at minimum speed for the rest of the way to the runway.

Lessons Learnt

Gareth and I discussed this at length, and I’ve been thinking about it ever since. I’m still hesitant to accept at ETD-00:30 or even ETD-00:60 that it’s reasonable/practical to plan on a 5 or more degree temperature rise over the next 30/60 minutes. Each degree of temperature you’re conservative on (read wrong about) means 1 or 2 tons of revenue cargo not carried. By the nature of the situation, you have to be conservative – else you end up in the situation we found ourselves.

Certainly the next time (Monday 22nd August – anyone want to change their travel plans now?) I’ll be far more reticent to accept a load anywhere near what we calculate to be the current or likely limit at takeoff. However, temporary gun-shyness does not an operational plan make. I know the situation is being reviewed by Flight Ops and I expect some kind of recommendation will be made shortly.

In summary:

1. It gets hot in Abu Dhabi in the Summer.
2. Between the hours of 11:00-13:00 you have to plan on a continually increasing temperature, perhaps even precipitously so.
3. Don’t count on the wind in these conditions.
4. Be proactive about cargo offload.
5. De-Fuelling is not an option to keep in your back pocket – it’s an absolute last resort that may not even be there when you go to use it. If you think you’re likely to need it – get it arranged early.
6. Sometimes you have to decide, sometimes you have to decide early, and operational efficiency and the profit margin need to take a second place to the requirement to get the job done.

Looking forward to the comments on this one.