Originally Posted by
Check Airman
Hi all,
A couple of 777 questions for those with the knowledge.
1. When selecting an APU to Pack takeoff in the fms, why is only one pack powered? If it can supply both at the gate, what’s the logic for only one during takeoff, and would a crew manually configure the system for the APU to supply both packs on a hot day?
2. When doing the flight control check, it why do you not select the flight control synoptic page? How do you know the surfaces are moving as required?
1. Because the hydraulic C1 and C2 air driven demand pumps need air to work. The APU cannot supply 2 packs and hydraulics for take off. If 2 packs are on with APU that would conflict with the right
bleed air. The left and right air systems have to be isolated for the APU to give the bleed air relief and hence the take off performance improvement.
2. the DSP plays no part in any non normal procedures for B777 and is stated as such in the FCTM. Only an EICAS message indicates a problem. For the flight control check you are looking for the EICAS FLIGHT CONTROL message to generate with the full and free movement. Missing indications on the DSP are no indication of a failure and as such should not be used for diagnosis. Again it’s all in the FCTM.