AF 447 Thread no. 4

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Stall recognition, et al

I can see that many here cannot appreciate how "benign" a deep stall is in a well-designed airplane. When the wreckage pattern was revealed, I began thinking "deep stall" versus stall-spin or structural damage or .... I came to my conclusion that the plane hit the water in a fully-developed deep stall when BEA provided impact angles and velocities.

So I posted my excerpts from the F-16 Code One magazine. It showed the pitch moment versus AoA for our little jet, and had the statement by a test pilot concerning what it felt like - a Sunday drive except for the rapidly unwinding altimeter. Due to great aerodynamics and a control feature that used the rudder to arrest yaw once A0A was beyond the normal "limit" ( out of control of the pilot, BTW, just the confusers trying to "help" you), there is little, if any, yaw. Due to our leading edge flaps we also had very little buffet to tell you, "hey, you hamburger, you just got us into a deep stall!".

I will guarantee you that if those pilots had seen the films of the Viper in a deep stall that they would have done something else than what they did. Further, except in "direct law", the confusers are still in the game, with various "protections" disabled. So the jet is still trying to "help".

In a fully-developed deep stall in a FBW jet you could let go of the control stick and the jet would be happy to continue the attitude, heading and AoA all the way to impact. After all, it is trying to reduce AoA and still trying to achieve 1 gee ( that's the Airbus, but in the Viper could be trimmed for anything from minus 2 gees +/- to plus 3.5 gees for a neutral stick). In this case, I feel the jet was still trying for the one gee, even at the AoA limit Hence, the THS kept creeping NU. Added gee command by the pilot didn't help, but the pilot could have let go and the jet would have still remained stalled due to c.g., pitch moments at the AoA, etc.

For those wondering about the THS trimming without an airspeed input to the confusers, the gee/rate sensors are completely independent of air data/AoA and are at the core of the FBW system implemented by the Airbus, same as for my jet and the Shuttle and ...... So to provide a 1 gee neutral stick, the gee sensors will move the THS accordingly to maintain the stick deflection command versus the neutral position/command (1 gee), and those puppies are VERY SENSITIVE and are sampled at a very high rate. Think inertial navigation accelerations like less than a hundredth of a gee. Those sensors also do not require an inertial "alignment", as they can be a simple as our old needle/ball doofers for rates and strapdown piezo-electric gizmos for accelerations on all three axis.

The data plot for this accident will reveal some great things about the Airbus aero, and seemingly excellent directional and lateral control capabilities even at a ridiculous AoA. It will also provide a basis for stall recognition and recovery procedures. I think we all want to see this, ya' think? Crying shame that we finally get the data at the expense of many people and an expensive jet.

Lest anyone think I am making excuses for the crew, I'll be clear - I AM!!! I'll admit that some of the control inputs are confusing. I'll also wonder what the CVR will reveal for about two and a half minutes as the crew ponders what the hell is going on. And then I'll try to imagine a revovery at night, in clouds and a confusing array of warning and caution indications. So there, I've said it.

respectfully,