On Sun, 29 Feb 2004 18:52:16 -0800, pacplyer wrote:

(Corky Scott snip

That will likely change when auto engines, complete with the
computerized ignition and fuel injection, and all the sensors to make it
work properly get into the air. But then again, the Lycomings and
Continentals would also benefit from such treatment.

Variable timing and fuel injection is coming, it's already running on
several models, it's called FADEC for Fully Automated Digital Electronic
Control.

Corky Scott

I think you are right Corky. FADEC (Full Authority Digital Engine
Control) has been around on jets since the 70's. It is unquestionably
the best way to reach TBO and optimum burn performance for an individual
engine. It however has resulted in unforeseen accidents (e.g: Airbus 330
in Toulouse, France, where test pilot got behind power curve, then pushed
throttles to the wall, and FADEC refused due to thermal spool up
considerations. Its programming decided that full power would be
available to the crew in something like five seconds. This saves millions
for the fleet every fiscal year. Problem was: The prototype hit the stand
of trees in something like six seconds… This was caught on video, and
the test pilot was interviewed in the hospital. He stated that nothing
happened when he called for max power. If I had FADEC in a single-engine
GA aircraft I would want a non-software override.

pacplyer

Two comments:

You've mixed up two different accidents here. The 330 at Toulouse was a
loss of control due to the aircraft (on autopilot) going way below VMCA
with one engine at idle and the other at full take-off thrust. The sat
and watched until it was too late to recover.

The accident you are referring to was the A320 at Mulhouse-Habsheim. The
pilot did a very low (30 ft AGL) pass with the thrust at idle. The speed
decreased til he was at full aft stick, riding on the AOA limiter just
above the stall. Then he realized that what he had thought were just low
bushes when he was looking down on them as he descended, were actually
trees that were higher than he was. He couldn't raise the nose, as
the fly-by-wire (FBW) was already on the AOA limiter, so the only way to
climb was to get more airspeed. He slammed the thrust levers forward, and
the FADEC accelerated the engine on its normal acceleration schedule.

Turbine engines run more efficiently if they are running close to the
surge line (i.e almost ready to compressor stall). But the engine has to
come closer to the surge line to accelerate. So the closer you run to the
surge line the slower acceleration you'll have.

FAR 25.119(a) requires go-around performance to be calculated using the
thrust that is available 8 seconds after a throttle slam from idle.
Manufacturers want the engine to run as efficiently as possible, but they
don't want to take a hit on the AFM go-around performance. So, they
typically design the fuel controls to allow full go-around thrust to be
reached in just less than 8 seconds from a throttle slam from idle. I've
done tests to check the acceleration on many transport category aircraft,
and the result is usually somewhere between 7 and 8 seconds, and this is
the same no matter whether the engine has a FADEC or an "old fashioned"
hydro-mechanical fuel control unit.

So don't blame the FADEC for the A320 accident at Mulhouse-Habsheim. It
was caused by a pilot who had way too much confidence in the low-speed
protections of the FBW. Fortunately the FBW prevented him from raising
the nose, as then the aircraft would have stalled, any many people would
probably have died. As it was "only" three live were lost.

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