Confiture said:
A4, what's the point to have Alpha Floor Protection if a GA is already initiated ... ?
Not sure you fully understand what you just wrote.
Ok, I can understand where you're coming from but what I was alluding to is this. Imagine a scenario where you are below 100' RA and suddenly the ground looms out the mist. Instinctively you haul the sidestick back but leave the T/LVR's in CLB - what will happen? No AlphaFloor (<100' RA) but AoA protection will activate? (> half stick). Sure, A/THR will increase thrust to try to maintain V
APP but it won't be AlphaFloor. AoA protection may well lower the nose initially.......... Don't forget we're talking here about flying around just above min speeds not 250 knots - the tolerence for activation is minimal.
FCOM
HIGH ANGLE OF ATTACK PROTECTION
Under normal law, when the angle of attack becomes greater than αprot, the system switches elevator control from normal mode to a protection mode, in which the angle of attack is proportional to sidestick deflection. That is, in the αprot range, from αprot to αmax, the sidestick commands directly. However, the angle of attack will not exceed αmax, even if the pilot gently pulls the sidestick all the way back. If the pilot releases the sidestick, the angle of attack returns to αprot and stays there.
This protection against stall and windshear has priority over all other protections. The autopilot disconnects at αprot + 1°.
V αprot, V αfloor, V αmax vary according to the weight and the configuration.
To deactivate the angle of attack protection, the pilot must push the sidestick :
- More than 8° forward, or
- More than 0.5° forward for at least 0.5 second, when < αmax.
In addition, below 200 feet, the angle of attack protection is also deactivated, when :
- Sidestick deflection is less than half nose-up, and
- Actual is less than αprot – 2°.
Rock and a hard place? Haul it back - no AlphaFloor and AoA protection active = negative flight path? Don't haul it back AoA protection not active - but if the levers aren't pushed a perhaps less than optimal spool up to try to maintain V
APP? In both cases the flight path is going to remain pretty similar which is not ideal close to the ground.
Once again, how to keep the Myth alive ...
But if you believe what you write, you should be able to quote it from the Official Report or at least publish some figures in that direction.
I don't wish to start a debate about Habsheim. I've tried to find the official report in English but can't. I do recall though on Air Crash Investigation that the claims of the Captain that when he pulled the stick back, the nose actually lowered were verified by the DFDR data. This was AoA protection. As he was below 200' RA (circa 30'-40' so no AlphaFloor) presumably he must have had more than half backstick otherwise it would have been deactivated.
Hope that clears up my thinking. I stand to be corrected and am only interested in sensible, technical debate - nothing else.
A4