B777 Flap Extension

With pilots come from a number of other aircraft types and several different airlines, including a domestic fleet, standardisation can be a challenge. The use of Flaps on approach has been in particular an interesting issue, which is hopefully address clearly in the following article.

Practices & Techniques : Flap Extension

During approach crew should ideally not extend flap to the next selection until approaching (within 20 knots) the minimum speed for the existing flap. Early flap extension results in unnecessary wear and tear on the flaps. On some Boeing types (notably the B747-400) there are Boeing and Company specific recommendations against the use of Speedbrake with any Flaps extended. The 777 FCTM recommends against significant Speedbrake extension with Flaps in excess of Flap 5 (due turbulence over the horizontal stabiliser). Other than this, Speedbrake is very much preferred over Flaps as a means of increasing drag on the aircraft when fast/high on descent/approach.

Unlike the 737, it is unusual for crew to skip standard flap settings during extension (other than F15/F25) and generally an indication of a poorly planned/managed initial approach. The “Standard” approach/Landing is Flap 1, Flap 5, Gear Down Flap 20, Flap 30.

Flap 15 on Approach

While specifically identified as a Takeoff Flap setting, the FCTM also refers to Flap 15 as suitable when manoeuvring prior to approach. Flap 15 is not recommended as a regular setting for a low drag approach – the FCTM specifically identifies the Gear Up / Flap 20 configuration for low drag during approach. The use of Flap 15 does not require pre-facing it with “Non Standard”. It’s just a flap setting.

Flap 25 on Approach

Flap 25 on the other hand is specifically denoted a Landing Flap Setting by the FCTM. Unlike Flap 15 – the selection of Flap 25 does not result in a “25” minimum speed indication on the airspeed tape. Typically PF calls for Flap 25 because of a fast/late approach where the aircraft is close to the Flap 30 limit speed. The lack of a minimum speed indication on the airspeed tape should be taken as an indication that Flap 25 should not be used during approach unless it’s the landing flap selection.