During takeoff, why throttle forward then raise hand from throttle to push a button, instead of pushing button then throttling?

Question

Preface: The comments assert the video to have been horizontally flipped, probably because (I am divining) the original belonged to someone else (user 'Jb380' if I remember)?

At 4 mins 3 secs of this video, the captain (who appears in the video on the right, but per the preface above, should be on the left) pushes forward the throttle, but from which he then removes his hand to use this same hand to push a button that changes an instrument display,

• from showing the tail view (camera) of the aircraft (to assist with taxiing???),
• to the primary flight display.

Afterward he replaces this hand back atop the throttle.

Why doesn't he instead push the button before deciding to takeoff and set takeoff thrust: this is safer than the above? For example, if abortion is decided exactly when nobody's hand is handling the throttle, then previous seconds needed to stop would be wasted?

Answer 1

Actually he does push the button before selecting takeoff thrust.

Often¹ the procedure on jets during take-off is to move the thrust levers about half way, wait for the engines to spool up and only then select TO/GA or Flex thrust as desired. In the video the pilot switches the display during this intermediate step. So the engines are not even spooled up yet and the aircraft is still moving slow. Plenty of time to stop if anything fails.

In fact even when nearing v₁ the reaction does not need to be that fast. The calculation of v₁ includes 2 s reaction time and correct response is more important. Look e.g. on this training video (it's A330, not A380, but the procedure is the same). The reaction is not that fast; they only retard the throttle after checking and calling the fault ("engine fire").

¹_{It used to be that the engines could flame out if you added fuel too quickly, but that's no longer the case now when engines are managed by FADEC (full authority digital engine computer). Some manufacturers/airlines/pilots maintain the procedure, most likely to avoid applying full power if one of the engines manifests some problem early. Or at least the pilot in this video does it.}

Answer 2

This is completely normal in Aircrafts like the A380 , Boieing 777 etc . Hands off at V1 (Engine failure recognition speed) is perfectly proper in an aircraft with multiple engines.

The throttles still moves , however the power setting (EPR) is in the computer and the precise setting of the engines is automated. The Pilot Flying the aircraft will still feel the throttles vibrating under his hand, but it's the auto throttle doing it, and not the flight engineer.

If Auto thrust is engaged, then there are 3 detents - Climb, Max Continuous/Flex and TOGA. If Autothrust is not engaged (at any time in the flight) then the thrust levers work just like the T/Ls on any other aircraft.

During take off, the T/Ls are placed either in TOGA (Take Off/Go Around) if the pilot is doing a max power T/O, or in Flex/Max Continuous detent if the pilot is doing a Flex power T/O. When the levers are in either of these detents the FADEC (Full authority digital engine control) will give the aircraft the max power available for that selection (It depends on the ambient conditions). When the aircraft reach the Thrust Reduction altitude the pilot may choose to move the levers backwards to the Climb detent, and will then get Climb power. The levers remain in this detent until the pilot reduces thrust to idle in the flare during the landing . This means that the FADEC will give the aircraft whatever power is necessary to achieve what you are trying to do - climb power for the climb, or whatever thrust is necessary to achieve your cruising Mach number, or desired rate of descent or whatever.

If an engine fails, then the levers on the remaining engines are moved back into the Flex/Max Continuous detent, and the aircraft will get Max Continuous power. If the pilot has to do a go-around at the destination, the pilot puts the levers into the TOGA detent and the aircraft will get all the power available.

Answer 3

Large engines, such as the ones on the A380 in the video, take time to accelerate. What the pilot in the video does is apply a small amount of power to ensure correct and balanced spool up of the engines. This prevents an uneven application of takeoff thrust i.e. if one or more engines are slow to spool on one side.

This procedure will likely be detailed in the standard operating procedures of the airline, on the aircraft I fly we advance to 1.15 EPR prior to selecting takeoff thrust.

He moves his hand to start his stopwatch (the Chrono button on the Airbus), this is to keep track of the amount of time the engines stay at takeoff thrust. This is important to monitor as, for instance, during an engine failure you may need that power to clear terrain and your climb will be slower - you don't want to damage your remaining engine(s) by maintaining a high thrust level for too long.

On the RB211 we have a limit of 10 to 15 minutes depending on the aircraft variant.

He doesn't push the button before moving the thrust levers to ensure max available time at takeoff thrust.