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Maisk Rotum
8th Nov 2018, 07:36
What is the history behind this? When was it introduced and was it in response to a specific incident, ie QF72?
Why do they not specify which ones to turn off (assuming 3 are working)?

Fursty Ferret
8th Nov 2018, 08:43
What is the history behind this? When was it introduced and was it in response to a specific incident, ie QF72?
Why do they not specify which ones to turn off (assuming 3 are working)?

It was in response to a pitch-down event on a Lufthansa A320 some years ago, where two AoA vanes froze during the climb. Eventually this caused the aircraft to introduce an increasing nose-down elevator input which was arrested, more or less, with full backstick. It's been fixed for some time now on our fleet.

Airbus elected to go for two ADRs as that'll force any Airbus into alternate law, as opposed to having separate procedures for A320, A330 etc.

The reason they don't specify is because it's individual choice over which ones go off. At my company it was pretty evenly split between PF (1 or 2) + 3; 1 + 2 (which left 3 available to either pilot); or 2 + 3 (leaving the Captain with instruments). I preferred the 1 + 2 option as control could be easily swapped between pilots.

Jonty
8th Nov 2018, 09:58
Given what may be happening to the aircraft at the time, I would just be pleased if either of us can reach 2 to switch them off!