The quality of this topic is very impressive - particularly from the engineers. Thank you. Here are a few insights.
Thrust Control on Finals
Thrust Control - Good guessing but lots of noise here ...
Eng 3 in ALTN Mode (N1 with -4% thrust protection) (Due EEC having insufficient valid signals to calculate TPR)
1+4 EEC errors logged. Degraded mode is purely due to loss of sensor inputs/EEC errors. Think of it as the engine in Direct Law (no thrust protections!) (Due EEC not able to calc TPR demand. So N1 commanded as a function of TRA and altitude)
One engine in a degraded mode does not cause another symmetrical engine into degrade mode. Airbus never matches thrust - it's against their philosophy "manual thrust is manual thrust!" - not like pseudo Boeing "manual thrust".
So 1 & 4 in Degraded (think Direct Law) Mode (no protections)
3 in ALTN mode (think Alternate Law with protections)
2 was in Degraded mode (not surprising given there were so few sensors left)
NO engines were in a normal mode.
This is why 1,2,4 had N1 centric displays (Degraded) and 3 had an TPR centric display (ALTN) (though thrust set via N1 with 4% pad).
Thrust control on 1,3,4 all 100% correct (but differing protections)
Auto Thrust inop due to MORE THAN 2 eng in Degraded Mode
1+4 thrust levers held constant to: (not in any manuals)
- permit very accurate (vernier) total thrust -> speed control on finals
- minimise thrust missmatch->yaw->roll->flight control demand on finals with thrust changes (ESSENTIAL when little excess roll control available)
1+4 WAS NOT held at constant thrust due to them being in Degraded Mode (illogical).
Conclusion: The three level 380s thrust system has incredible fail operational capability.
WING STRENGTH- Not a problem. Wing loaded ~23% to ultimate limit (1.1/2.5 X 440/569 X 1/1.5) (Max 20 deg AOB/MaxG, Wt/MTOW, Ultimate Load factor)
- Airbus supercritical wings are VERY aft-loaded.
- Leading spar only contributes 5% strength - it's more scaffolding for the leading edge