Airbus crash/training flight

[fdr]

stall

Hi BOAC.

at the point of stall, or dependent on other factors at a point consistent with approach speed/1.3... the controls should not exhibit any abnormal responses. AoA can be achieved through 360 degrees... ( my rotor blades achieve various AoA's within 0.π to 2.π.... per rev dependent on radial velocity Ω, radius, r/R and translational speed of the rotor system in the airmass, ie inboard section of the span achieves 11/12.π at ψ=180) but the normal regime for a transport is around 0.π to π/12, a very limited sector of operations. From π/2 to 3/2.π the flow is full reversal. As far as adverse aileron roll is concerned there are boundaries of operation where the coefficient of lift v AoA, or "a" slope doesn't decrease with increasing AoA above stall. Equally, drag does not act in a linear manner at extreme AoA's either.

At an α>15 ( π/12) approx to α<30 ( π/6), ie a normal high α > Vs 1g stall α, then it is quite normal to get some control reversal due to the change of the a slope. Discounting the roll spoiler action, the change of section α for the L and R aileron acting differentially needs to be exceeded by the reduced a slope on the section with the downward deflected aileron. This can be avoided by good design of the section and the differential deflections.

With respect to adverse aileron yaw, it is rather moot with a mixed aileron/spoiler roll control, where the spoiler drag exceeds the drag of the aileron pretty much at any α from 0.π to 2.π, ie within a 360 degree rotation of a section.

The A320 accident merely shows a period of behavior within the certified envelope area where there may be some reversal occurring, which is of interest, particularly as an A-PC issue will undoubtedly be held over the pilots head.

To simplify the above, in an aerodynamic stall of a B737 or a B747, the ailerons remain effective at and around the point of break, with normal response, and no exceptional piloting skills needed. The B747 particularly is very nice. Don't do this at home The A320 on the other hand was never tested in this region and the behavior is interesting to this observer, who has examined A-PC issues with this type before. The MD11 ailerons work nicely through stall as well, (but a stall at other than low speed/1.0g will often result in severe damage to the elevators, including delamination of the skins and fracture of the elevator spar... again, don't do this at home...) Having said all the above, which probably amounts to little, the certification process of RPT aircraft is remarkably thorough, but on occasions events conspire to show room for improvement. I would think that the out of trim case for the AI aircraft, and some TBC products still could be improved as we pilots do get to occasionally operate in odd parts of the envelope.

(Probably the greatest control reversal event in recent times was a B737-400, of Adam Air KI 574, which well exceeded the design envelope of the aircraft, and achieved recorded data of roll in the opposite direction of the ailerons/spoilers due to aeroelastic deformation... then it broke up... being operated well beyond the design limits of the aircraft. Shades of Quill & DeHavilland etc...).

Stuff Happens, and the pilot has seconds to deal with it, whereas scientists have years to study it... Unfortunate turn of events led to the event occurring, but the recovery part hardly was a failure of the crew, perhaps I would feel differently if the aerodynamic package for the sims incorporated what we know about dynamics outside of the certified envelope, but at this time the majority of sims are of questionable value outside of the normal envelope, and on occasions negative training (MD11 sim, full aerodynamic stall, ROC 6000FPM for 2 minutes...., B737 stall with full rudder deflection, wings recovered by aileron... B777/B744 50knot Xwind full wrong aileron, wings level to rotate...).

(π= PI, btw.... )

FDR


PS: the problem here from a handling point is the out of trim situation, a bit of "rock and roll" would assist in stopping the attitude from getting higher still due to the out of trim condition.... roll is of interest from a certification point but is far less concern than the out of trim case, or the fact that the failure of AoA probes was not identified and annunciated as a failure to the crew when this condition occurred.