I doubt any recovery was possible, even theoretically, with so little altitude.
The strategy would be to go with the rotation to inverted as quickly as possible, then apply full aileron against the rotation to remain approximately inverted for a moment while applying max negative lift (stick forward) without stalling, to stop the descent and preserve altitude. But then the engine would quit, and likely not enough energy (altitude+airspeed) would be available for rolling out of inverted.
Even if theoretically possible, I do not thing there was any way the pilot could have made a rational decision to do anything else than what he did – applying full aileron against the roll hoping to get out of the wake again quickly.
How about applying a lot of left aileron (i.e. against the direction of the roll), but not quite full, so that the track flown departs off to the right, and at the same time maximum left rudder?
Someone will point out that is what broke the tail off that Airbus in NY in 2001, but it should not break up a light GA type especially at low speeds.
The idea would be to exit the wake, to the right.
Even if theoretically possible, I do not thing there was any way the pilot could have made a rational decision to do anything else than what he did – applying full aileron against the roll hoping to get out of the wake again quickly.
I agree; I would have tried that, but used the rudder also.
Here is an interview with (I guess) the pilot. In German
http://www.bfu-web.de/videos/Flugunfall_Backnang-Heiningen_Final.mp4
Peter wrote:
Here is an interview with (I guess) the pilot. In German
Not the pilot (don’t think you can interview him anymore, sadly), but the accident investigator. Very impressive! To sum it up:
In the simulation they showed the sinking of the rotors until about 30ft above ground where they more or less stayed, the technician says something about ground effect but doesn’t expand on it. They then ran the test with the colored smoke and finally took an AN-2 and a DR-400 to 2000ft to try it for real. According to the test pilot it took a few attempts to really hit the wake, but when they did, the Robin got flipped over 90degs w/o sufficient control authority to counteract the move. Verdict by the test pilot: if that happens near the ground, you’re dead. He also commented on the extremely rapid onset that apparently surprised even him, although he was of course prepared. In a WTF moment 30 feet above ground you don’t stand a chance….
I have never heard about ‘ground effect’ for rotors – anyone else here?? I always thought they’d dissipate once hitting the ground. Looks like they can linger. Nasty…..
Peter wrote:
interview
Nice to see he’s back in the saddle again.
His mate is a bit daft IMO, as he got himself in the same spot of bother on a flight later on in the video.
Again it’s a fellow flying a Robin…need not say anymore.
Good job he was too high on final this time. Could have had a nasty ending if any lower. 
Peter wrote:
Someone will point out that is what broke the tail off that Airbus in NY in 2001,
IIRC correctly what broke the tail of that Airbus was that the FO rapidly alternated between max left and right rudder — it was not a single max rudder deflection.
Some aircraft actually publish Va for the different axes, for example the Texan/Harvard T-6 has a Va of 140 MPH IAS in pitch for positive manoeuvres, 190 mph in roll, but you only use 155 mph to avoid aileron buffet, and only 90 mph in yaw. The envelope is +5.66 g/-2.33 g, but this I believe is only in pitch, combining pitch, and or roll/yaw will reduce the envelope. This implies a low tolerance for full rudder deflection above quite low speeds, and also quite low fin stall speeds, Va being a function of un-accelerated stall speed. It is a gentle beast in positive manoeuvres, somewhat like a 1940s Buick or Packard, but the wing is quite snappy in the stall.
Large transports have rudder limiting devices above certain speeds, similar to reduced, half bank autopilot mode above FL200 etc. The AA accident presumably had this device fitted so it would be interesting to understand why alternating deflection caused a failure.
RobertL18C wrote:
The AA accident presumably had this device fitted so it would be interesting to understand why alternating deflection caused a failure.
IIRC there was no rudder limitor on the A300.
Peter wrote:
Someone will point out that is what broke the tail off that Airbus in NY in 2001, but it should not break up a light GA type especially at low speeds.
If we’re both thinking of the same accident, that tail broke because the pilot was rapidly alternating between large deflections to the left and right. The issue was that Va is for one full deflection. Actual performance of that particular aircraft was way above design limits, IIRC.
The question is how big is the rotor compared to your wingspan. If your wings are too short, you’re screwed. Maybe if you were going fast (I mean really fast) in an unlimited aerobat. XA41 can do up to 450 degrees per second, IIRC. If you don’t have enough authority to catch it, you will IMO exit the rotor too low to recover.
Good reminder for anyone flying light aircraft. Thanks for posting.
Sad too.
