Which Autopilot is engaged
Joined: Mar 2009
Posts: 273
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From: Kerikeri, New Zealand or Noosa Queensland. Depending on the time of year!
I can't comment on the 777 specifically but when multiple systems are fitted to aircraft airlines often adopt a policy of alternating usage. i.e Unit 1 on outbound flights, Unit 2 on return flights. Or Capt flying Unit 1 and F/O Unit 2.
Does this help? Cheers
Does this help? Cheers
Joined: Feb 2010
Posts: 18
Likes: 0
From: Texas/Tripoli
Can you clarify what you are asking?
You should think of it as having 1 "autopilot" or auto flight control system, with 3 processors. If one or more fails, you'll have some annunciations to that effect, but it isn't important which individual processors have failed. They are identical. Nor is it necessary to know which one is active. Typically, computer systems like these will "power on self test" and then select the channel or processor that wasn't used previously.
Think of it like this: If you have a lamp with three light bulbs and one goes out, does it matter which one went out? It just isn't as bright, and you know you need to change a light bulb.
You should think of it as having 1 "autopilot" or auto flight control system, with 3 processors. If one or more fails, you'll have some annunciations to that effect, but it isn't important which individual processors have failed. They are identical. Nor is it necessary to know which one is active. Typically, computer systems like these will "power on self test" and then select the channel or processor that wasn't used previously.
Think of it like this: If you have a lamp with three light bulbs and one goes out, does it matter which one went out? It just isn't as bright, and you know you need to change a light bulb.
Joined: May 1999
Posts: 21
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From: Riyadh, Saudi Arabia
Grounded27 is spot on. Whether you engage the A/P using the left or right hand side button merely affects which altimeter reference it uses and that's annunciated by the little L or R under the baro reference on the PFD.
Joined: Oct 2010
Posts: 5
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From: London
As I recall, in normal circumstances, all 3 are engaged in cruise, but one is the master and the other two are slaves. The centre does not have any backdrive capability for the controls so can never be master, as someone else pointed out. I heard a rumour the right becomes the master the first time it is engaged after power up, and then it alternates each time it is re-engaged, but you'll never be able to tell in the flight deck.
