Originally Posted by Jazz Hands
At 2:10:23 the thrust lock mode was "de-activated".
If the autothrust was already disengaged, how does one then de-activate the thrust lock?
Is there a button to push, or can it only be done by manually moving the thrust levers?
a) one need to understand why the "THRUST LOCK" function was activated:
In our case, it means that AUTOTHRUST disconnection was due to a system fault and not to any pilot action (like using the disconnect pb, or setting levers to IDLE).
Consequently, thrust will remain locked at its last setting which is unrelated with THRUST LEVERS actual position: at cruise at FL350, with turbulence, thrust could be anywhere between IDLE thrust and CL thrust = (MIN-MAX range: this is autothrust range of operation when active and engaged - MCT is only used in case of one engine failure). Hence, when A/THR disconnect, actual Thrust doesn't change (increase to CLB if actually set below this level), it is
locked.
b) What caused the loss of A/THR was both FMGS (auto flight system) faulting due to their IAS monitoring function (A/THR fault is recorded at 0210:08, three seconds after A/P OFF at 0210:05).
c) Unlocking THRUST action is only manual by moving the levers. If one re-engage them where they already were set (CL detent), like in our case, DFDR record won't show any change of detent setting: they were set off CL detent, moved and engaged back in CL detent. Nonetheless, DFDR will record the manual action of Unlocking the Thrust and the total duration of the "THR LOCK" period before crew reaction (about 15 seconds).
During this period (0210:08-0210:23), thrust was locked at N1% 83.
@ FL350, standard settings for pitch/thrust should have been adjusted to:
Mach .80 ; GW > 190 t ; pitch =
3.5°
Mach .80 (260 kt) ; 200 t > GW < 210 t =
91.9 > N1% < 93.1
@ FL370:
Mach .80 ; 200 t > GW < 210 t =
94.3 > N1% < 95.9
And, of course, there is no N1 value for above levels.
Consequently, she was starting to climb up to FL380, at an high V/S and pitch rate (close to take off), without initialy enough thrust to maintain FL250 in level flight (as she was decelerating just prior this sequence started). It took about 25 seconds to manually increase N1 up to 104% while she had already bleeded a good deal of her speed in between.
