On Thu, 28 Sep 2006 05:56:24 +0200, Mxsmanic
wrote:

RK Henry writes:

Don't underestimate the capabilities of a trained, experienced crew to
cope with equipment failure. Case in point, United flight 232 at Sioux
City, Iowa. Despite complete hydraulic loss and concomitant loss of
flight controls the crew was able to bring the aircraft to what turned
out to be a survivable crash for most of the occupants.

They were also flying an aircraft that did not have fly-by-wire
systems.

Fly-by-wire means that no command bypasses the computer. If the
computer malfunctions, or if it decides to ignore your command, you're
out of luck, and no amount of skill will help you. If flight 232 had
been a fly-by-wire aircraft, everyone aboard would have died.

The similarity is that in both cases there's no hard connection
between the control surfaces and the flight controls. The DC-10 had no
cables between the controls and the flight surfaces, just pipes, so
with no hydraulic power there was no control action at all. But the
crew was left with control of the engines and that made it possible to
control the airplane. My assertion is that there is insufficient
evidence to conclude that everyone would have died had the airplane
been FBW. Uncertainty remains as to that outcome.

However, much as it may disturb some other, less tolerant, members of
this group, I tend to agree with your qualms about FBW. FBW makes it
possible to implement exotic airframe designs by defining their flight
characteristics in software instead of in hardware. That's fine when
the pilot sits in an ejection seat, but when this technology is
extended to airplanes whose occupants don't have the option of pulling
a handle when things go badly then we must be very careful. I'm sure
the problems can be solved, probably with multiple redundancy, but a
century of experience with aviation shows that we must always consider
the possibility of failure.

I've been similarly apprehensive about glass cockpits in light
aircraft. A single point of failure in an inadequately designed and
tested system could conceivably leave a pilot deaf, dumb, and blind.
Show me the test plan.

RK Henry