Maybe I am incorrect, but I suspect any autopilot and/or terrain proximity system can be ignored, and thus “deliberately” over-ridden. They provide warnings to prevent an accident, but if the warnings are ignored, then an accident is still possible?
Likewise, a computer controlled FBW system may not prevent you doing something inherently dangerous, all it will do is ensure that the aircraft can be flown to it’s maximum performance in the situation without departing from controlled flight. However, if you can apply sufficient bank to dig the wing tip into the dirt without first stalling the aircraft first, I suspect the FBW might let you – or are such systems clever enough to know the exact height of the wingtip above the ground and also able to predict the position and height of any non-permanent obstacles on the airfield?
I doubt the FBW has the ability to predict engine failure due to bird strike, or to predict wind shear or wind shift. In such circumstances the outcome will be the same, the FBW will do it’s best to maximise performance after the event has ocurred, such as to achieve max climb performance if requested by control input, whilst limiting bank to avoid stall/spin entry etc, but if the aircraft is too low or too slow to recover, it may still hit the ground.
It’s a bit like trusting to your ABS when tail-gating on a motorway at 70mph – the ABS will ensure the car stops in the minimum possible distance at any speed, however, that stopping distance will increase with speed (basic laws of physics apply regardless of ABS). So if the ABS can stop the car in say 100 yards at 70mph, and you choose to drive at that speed but at less than 100 yards behind the car in front than you will still hit it if it stops suddenly, all the ABS will do is ensure that you will be hitting it at the slowest possible speed when you reach it.
Likewise, if the Airbus is being flown lower than the operating limit of the FBW would expect, then perhaps sufficient angle of bank could be applied to get the wingtip into the dirt or into an obstacle. Or, if wind speed suddenly dropped by 10mph due to gusting, or an engine failed due to bird strike, then FBW may not be able to compensate for the loss in airspeed or the sudden assymetric thrust before some part of the plane touches the ground – at which point it all gets very unpleasant.
If I am wrong, and FBW really does make the aircraft “idiot proof” and “crash proof” please correct me, but all I believe it does is ensure an aircraft can be safely operated to it’s absolute max performance in any situation. However, if that situation is changed by unexpected external influences, then the FBW may not be able to “re-optimise” things back to the new “maximum performance” as adjusted to suit the new conditions, before the aircraft runs out of height and/or airspeed and hits the ground?
Paul F
im sure there are people out there who know more than i do about airbus systems, i did some work experience with airbus a year or two back, and a senior-ish chap explained that all of the pilots command inputs go through the computer, none of his controls are “Directly” linked to any of the surfaces/ engines. he makes a movement or change in throttle etc and the autopilot computer decides whether or not to allow him to make that manouvre, taking into context altitude, ground speed etc. i seem to remember the incident wher the airbus ended up in the trees, was a glitch in the autopilot program, where it thought the pilot was landing, when he was just doing a low pass, and it wouldn’t allow him to apply full throttle to climb, so in the trees he went 🙁
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