Ron Garret writes:

First, he said he didn't really know because he'd never actually
tried it.

Ah ... well, that pretty much invalidates the rest, doesn't it?

Company policy forbids disconnection of the autopilot in cruise.

I thought it might.

The airplane is unstable enough that doing so is actually
potentially dangerous.

No, it's not unstable or dangerous. The purpose of the autopilot rule
is to ensure maximum fuel economy. Even the best pilot will consume
more fuel flying the aircraft by hand than will a flight management
system (which is designed in part to ensure economy).

To keep the plane flying safely without the autopilot at cruise
requires constant attention.

How frequent is "constant"?

An autopilot failure in cruise (unlikely because there are redundant
autopilots) is an emergency which requires immediate diversion to the
nearest airport.

It sounds like he's repeating what he was told. He's already admitted
to you that he hasn't tried it.

Bottom line is that a 757 handles not much differently from any other
heavy, clean plane. In perfectly smooth air if you have it perfectly
trimmed you might have a minute or two at the outside. Under realistic
conditions (a little turbulence, less than perfect trim) you have a few
tens of seconds before you are in an unrecoverable roll. In bad weather
you could be unrecoverable in only a few seconds, but that would be
unusual. It's not like a helicopter where if you take your hands off
the stick for a few seconds you're pretty much guaranteed to die.

Have you tried it? Your pilot friend hasn't. Neither have I.
Commercial airliners are not aerobatic planes or fighters, though, and
I rather doubt that they'd be designed for anything less than very
high stability. They'll never be making any drastic movements, after
all.

He also said you'd get altitude excursions sooner than roll excursions.

But of course he didn't really know.

This is consistent with my personal experience which is that as planes
get faster (and my personal experience covers a range of 90-180 KTAS
cruise speed) they get harder and harder to trim for pitch.

That's the first 180 knots. Only 1400 or so to go.

In summary, your friend and you don't know any better than I do. Do
you see why I feel compelled to question the assertions I read?

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