Interesting post by 320 driver.
I believe it aptly demonstrate my point about the "blind faith" some A320 drivers exhibit toward a design that over-rides the pilots command to miss the rocks since it's programed to instead save the airframe. The F-16 community went through a similar overconfidence in it's FBW introduction: that the airplane could get you out of any problem, with predictable fatal results. We're agreed then, that the studies of GPWS escape maneuvers at low altitude come into play AFTER Controlled Flight Into Terrain is avoided with an aggressive pull up, not before, in the scenario I refer to. I'm talking about a visual impact with hills due to a gross navigational error down low, and not spotted until too late. O.K, 7 g's was a lethal exaggeration.
How about 3.5 G's? (thanks for the correction CONF iture).
Me? I prefer to bend the wings and miss the rocks, as was done on several aircraft that made it back alive due to the ability to temporarily exceed the design limits. I am aware of McDonald Douglas and Boeing events which were classified as accidents since the airframe was severely damaged in over-g pull ups. In Good Aerospace engineering, failure limit loads are not the same as operational limits, and have something like a ten to thirty percent additional protection before airframe yield occurs. Additionally, if an airplane is designed correctly, it will progressively fail, shedding outer structure before the spars completely fail.
I admit that I am completely ignorant how a profession pilot would worry about saving his airframe if rocks are looming in the windshield as they apparently were in Pakistan recently. Who cares about the airframe in this scenario? Miss the rocks at all costs, then, if you're still alive, hope you can limp back to the runway. But not in FBW as I understand it. In FBW you are not in command. The HAL-9000 is in command:
"I'm sorry Dave, I'm afraid I can't give you four g's right now, it might bend the titanium spar". BOOM.
Let me try to rephrase the question: Due to rapidly rising topography, if it takes say 3.8 g's immediate pull up in two seconds time to miss a rock outcrop and your A320 is given this command with full back stick, will it follow it?
No, it won't as I understand it. It will respect the load limit algorithm and only give you something like less than 2.x g's. Initially, in this case, the G limiting subroutine will overide any available angle of attack considerations.
Right?
Congratulations! We have saved the airframe for two seconds, but lost a hundred souls and the airframe in three!
Now I feel this is a design oversight. When I use that term or the term software`-shortcoming it's extremely upsetting to Dozy and others, however, it's not surprising. Aviation history is replete with design oversights. Don't worry Dozy, We are not blaming programmers (CEO's and flight management get that distinction), and besides, the event we're discussing is extremely unlikely an occurrence. But if it happens and you need say 80 degrees bank to miss the rock cliffs, you better pray you're in a Boeing.
By the way, I like FADEC, and it does do a great job most of the time (except at Heathrow with the dual "roll back" on final with the BA 777 and on dozens of airbuses over the years.)
However, sometimes FADEC can't accelerate at it's full potential: if the airbus is in Level Change the FCP schedules a slow-spool up for pax comfort/tbo etc, and hits the trees, because:
It doesn't know the whole flying picture.
Only the pilot flying knows that. And only if he's not lulled to sleep riding around on autopilot watching the pfd FMA clicking through mindless modes that don't really keep the pilot informed as to what's happening unless you're staring right at it all the time. Which is why way back in 1995, AW&ST concluded that Airbus automation actually increases pilot workload, rather than reducing it as was advertised.
For me on the A-310's the answer was massive consumption of coffee making me a nervous wreck since I never knew when the damn thing was going to attempt a tail-slide or turn the wrong way, which it always did. It was like a bad student who had to be constantly watched.
Admiral and others are correct, 7 g's is GA stuff, my bad.
320 driver said:
No-one to my knowledge has ever 'fostered the habit' of flying on the back of the curve at low level (and I have been flying this machine for 16 years). It is a facility that can be useful in certain unusual situations. Flying the aircraft at SOP speeds (O, F, S) keeps you right in the flat part of the curve. If you are operating on the back of the curve then it is your poor practice, not a defect of the aircraft, its makers or its operating philosophy.
320 driver, you seem unaware of the early history of airbus. For example here was an accident by one of the chief pilots resulting in the first A320 fatalities:
Air France Flight 296 was a chartered flight of a newly-delivered
fly-by-wire Airbus A320-111 operated by
Air France. On June 26, 1988, as part of an air show it was scheduled to fly over
Mulhouse-Habsheim Airport (
ICAO code LFGB) at a low speed with landing gear down at an altitude of 100 feet, but instead slowly descended to 30 feet before crashing into the tops of trees beyond the runway. Three passengers died. The cause of the accident is disputed, as many irregularities were later revealed by the accident investigation. This was the first ever crash involving an
Airbus A320
The official report states
[1] the causes of the accident were:
- Very low flyover height, lower than surrounding obstacles.
- Very low speed, reduced to reach maximum possible angle of attack.
- Engines idling during flight.
- Late application of go-around power.
This combination led to the impact of the aircraft with the trees.
The Commission believed that if the descent below 100 feet was not deliberate, it may have resulted from failure to take proper account of the visual and aural information intended to give the height of the aircraft.
[edit] A320 operation anomalies
Third-party investigations into the crash dispute the official findings.
[2] Captain Asseline asserted the altimeter read 100 feet (30 m) despite video evidence that the plane was as low as 30 feet (10 m). He also reported that the engines didn't respond to his throttle input as he attempted to increase power. The month prior to the accident,
Airbus posted two
Operational Engineering Bulletins indicating anomalous behaviour noted in the A320 aircraft. These bulletins were received by Air France but not sent out to pilots until after the accident:
[edit] OEB 19/1: Engine Acceleration Deficiency at Low Altitude
This OEB noted that the engines may not respond to throttle input at low altitude.
Air France Flight 296 - Wikipedia, the free encyclopedia
Also, you might want to read up on the recent splashdown of an A320 in Europe, and the dozens of alpha mode mishaps and accidents on the A300/A310's if you are unaware of them. Everybody and every property produces different flying experiences, I'm sure. But the cult of a "magic airplane", as another poster put it, used to be a big part of airbus culture and was dangerous imho.
Studies have shown, that humans are very poor at monitoring automation. Although man does not live by hand alone, hand flying proficiency is essential imho to avoid all these coupled disasters that plague the industry. If you hand-fly you actually reduce crew workload and increase safety imho. If you operate as well, with manual thrust, you are better prepared for unexpected events like AF447 when, at dark of night, outto drops out and throws it all in your lap . But how do you retain hand flying skills in an airplane which calculates your bank angle and back pressure for you, and just when you need it most falls into manual law?
CC