Originally Posted by
vilas
The following information was released by Airbus in Sochi crash investigation:
The logic of integration of the autopilot/flight director (AP/FD) pitch control and the
autothrust control
¬If AP/FD pitch mode controls a vertical trajectory (e.g. V/S, ALT), then AT
controls speed.
¬If AP/FD pitch mode controls a speed (e.g. OP CLB), then AT controls thrust.
¬If no AP/FD pitch mode is engaged, then АТ controls speed.
Logic sequence of the OPEN CLB mode
¬for level change more than 1200 ft:
¬at OPEN CLB mode engagement by the pilot, V/S control with V/S target = +
8000 ft/min (40 m/s) is applied for AP/FD, and SPEED/MACH mode is engaged
for AT
¬when engine N1 reaches 95% N1CLB mode, AP/FD switches to SPEED/MACH
control law, whereas AT switches to the THRUST mode
¬Throughout this time the FMA displays THR CLB for AT and OP CLB for
AP/FD
The given scheme of engagement for the OPEN CLB mode ensures the uniformity
of the aircraft response in all configurations and within the whole range of the flight altitudes and
speeds.
¬For level change less than 1200 ft:
¬at OPEN CLB mode engagement by the pilot, V/S control with V/S target = +
1000 ft/min (5 m/s) is applied for AP/FD, and SPEED/MACH mode is engaged
for AT
¬ Throughout this time FMA displays THR CLB for AT and OP CLB for AP/FD
In this case the climb is in fact performed in the vertical speed control mode.
***
It should also be noted that if the OPEN CLB mode is engaged less than 30 seconds after the
aircraft level off function is activated, the autopilot is authorized to use the vertical acceleration at the maximum value of 0.3g, whereas usually it is only 0.15g.
In the automatic flight, when the OPEN CLIMB mode was engaged, the aircraft started climbing
rapidly, at a vertical speed up to 12 m/s, with pitch angle increased to 21º by 22:12:06, maximum
vertical acceleration 1.27g, maximum angle of attack 10.7º, and the indicated airspeed reduced to
129 kt (240 km/h), which is 8 kt lower than the target speed. Engine r.p.m. were increased to the
maximum possible value for the given position of the thrust control levers (Attachment 2, Fig.4).
Thanks vilas. Can always count on you to teach me something I didn’t know. Will pay attention to this in a few hours.