Originally Posted by
Vessbot
Neat - but we're like 3 back and forths in this exchange, and you still haven't said what this "good reason" might be - or elaborated on "Two rockers don't actually give any particular advantage."
Well, actually I have offered some possible reasons; Check posts 6, 19, 24, and 33 again.
What I keep trying to say is that us here not knowing the reason does not mean there is not a good reason !
Airbus - hugely successful and with vastly more knowledge, engineering and design qualifications than us - will have identified good reason(s), otherwise they wouldn't have designed it that way !
With my engineering background, and 20 years flying Airbus and Boeing, and other types on the line; I can make an educated guess at reasons if you want ?
A single rocker is:
Simpler mechanically.
More robust.
Larger and easier to operate.
Easier to seal against dust ingress.
More reliable.
Has no operational disadvantage over two rockers any more, (with modern electronics and fault detection systems).
Some have said that two rockers allow a pilot to know when one switch is becoming faulty and intermittent, but the same is true of Airbus' single rocker and their associated monitoring electronics.
Back in the day when the pitch trim was a simple switch controlling an electric motor, and aircraft were electrical and hydro-mechanical only; two switches wired in series and two rockers were a sensible way of preventing trim runaways over a single basic switch arrangement, since any basic electrical switch can potentially collapse internally or weld on.
But with electronic fault monitoring; two separate rockers have become unnecessary, since there are still two switches under the single rocker, and any single switch failure or "stickiness" can be detected and mitigated by the electronics or the pilots.
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