Originally Posted by
Uplinker
I have never known an Airbus FBW autopilot to suddenly drop out by itself* nor have I ever seen one do something weird uncommanded - and we had some pretty old Airbuses. In my experience, they are very reliable and dependable.
If the autopilot is off then obviously one should be grasping the side stick. However, owing to the fly-by-wire, if one was hand flying in smooth air and needed to scratch one’s nose while the other hand was holding the deployed speed brake, say, nothing untoward will happen if the side stick is left for a couple of seconds. Obviously, if one was hand flying a turbulent approach requiring constant and rapid changes to correct the flight path, then a hand should always stay on the side stick.
If the autopilot is on, there is no need although it is a sensible precaution during an autoland or turbulence - one is controlling the flight from the FCU or the FMGS - and the side-stick is locked in neutral anyway.
Holding a locked side stick until FL100 seems unnecessary to me.
*It did drop out when the iPad and its mount fell off the window onto the locked side stick !
AAIB Bulletin 6/2001
The A330 commander's report
Both aircraft were in clear air as the A330 was slowly overtaking the A340 below it. The A330 commander stated that his aircraft was slightly to the right of the A340 and almost abeam it when he saw the A340's wings start to flex. At about that time he felt a bump, which he described as similar to entering a mountain wave. Five to ten seconds later there was another bump during which the A330's altimeter reading descreased by 200 feet. Immediately thereafter, the A330 commander heard a TCAS "climb climb" warning and he noted that the A340 TCAS symbol had changed colour to red on his navigation display. He looked out and down at the A340 which was some 200 to 300 feet to his left in a nose-up attitude and climbing steeply. The A340 passed through the A330's level before the commander had time to react to the TCAS warning and the TCAS was still issuing a "climb" instruction for a short while after the A340 had climbed above the A330. The commander continued to minor the A340 visually and on TCAS. It appeared to reach an apogee above FL380 although by this time it had fallen behind the A330. Nevertheless, it was still laterally quite close to the A330's track so the commander altered course to the right to make space for the A340 to descend back to FL 360. After a short discussion with the A340 crew on VHF radio, the A330 commander broadcast a warning of severe turbulence on the common VHF frequency and then reported both the turbulence and the aircraft proximity (AIRPROX) occurrence to Shanwick on HF Radio. there were no injuries on board the A330 although there were spillages in the cabin.
The A340 commander's report
At FL 360 the A340 was 1000 feet below the maximum cruising level displayed on the Flight Management and Guidance System (FMGS). The commander was expecting a turbulence encounter around 59°N 20°W and when the aircraft first entered light turbulence he made a cabin announcement and switched on the seat belt signs. Shortly before the AIRPROX event he experienced moderate turbulence and noticed outside air temperature changes. Suddenly the aircraft began to climb, the Master Warning sounded and the autopilot self-disengaged as the aircraft exceeded the speed limit of 0.86 Mach
AAIB Bulletin No: 6/2001 Ref: EW/C2000/10/2 Category: 1.1