Re: over-automation with glass cockpits

From: (Robert Dorsett)
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
Date:         30 Jul 96 01:33:01 
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In article <airliners.1996.1454@ohare.Chicago.COM> Rob Tremblay <> writes:
>Unfortunatly, I think you may suffer from what many others suffer
>from- comparing a civilian jetliner with a F-22. Two different
>airplanes, two different jobs. 9 G turns are simply not required in
>a civilian airliner. Large jets are designed to do 30 degree bank
>turns to final at 5 miles back- not exactly a manuever that an
>autopilot can't handle.

With a fleet of aging aircraft and various types of new failure modes--
ranging from structural failure to partial control system failure to
bombs--it is both foolhardy and idiotic to restrict pilot authority to
merely what an autopilot can handle.  There have been several incidents in
which the crews have sustained high G's--in many cases, loadings far in
excess of design limits were encountered.

>> I also realize that some tiny additional increment in safety may be
>> achieved by automatically preventing overstressing the airframe by a
>> ham-handed pilot, but surely this is the classic case of a solution
>> looking for a problem.
>The Airbus has a safety feature that only allows a pilot to pull the
>maximum g-limit of the airplane- no more.

What exactly is that limit?  What the Feds say it should be?  25% more?
The "limit" is a constant which some aerospace engineer decides is the limit.
It may or may not have anything to do with the inherent properties of the
structure: it may be influenced heavily by Legal; it may be influenced by
marketing constraints.  It may actually be a variable limit which can drift
due to variations in the manufacturing process.

The absolute limit cannot be established.  Yet in real life, crews rarely
come anywhere near that limit.  When they do, it's usually because the shit
has hit the fan and extreme measures are necessary to either control the
airplane or create a crater in the ground.

>Why would you want to
>overstress the airframe?

To save the lives of its passengers.  Who cares if you land with a bent
wing, if being allowed to *bend* the wing allows the recovery of the
situation?  Do you think the captain of that Aeroflot A310 cared how many
G's he was pulling as he flew into the ground?

>Once again, we are not talking WW2 flak
>avoidance here- we are talking about getting passengers from point
>A to point B without a G-suit.

Which works fine if all you fly is a simulator.  When you step into real
life, which is replete with airlines using forklifts to attach engines, real-
world weather, other airplanes to bump into, and, yes, the occasional nut
with a bomb, it gets a tad more complicated.

Robert Dorsett                         Moderator, sci.aeronautics.simulation