Quit stalling – please!

August 10, 2011 by Bruce Landsberg

As the Air France 447 accident investigation continues forward, a few themes apply to all aircraft regardless of size. Unexpected stalls are bad, the indication of the stall should be unambiguous, and perhaps most importantly, the wing needs to be unloaded to resume flight. It seems so basic and yet every week, at least in GA, somebody exhibits poor airmanship that results in at least damage to the aircraft and sometimes worse.

There have been calls for improved airmanship since the Colgan Q400 accident in Buffalo where the captain allowed the aircraft, on autopilot to level off and, under reduced power, settle into a stall. The stick shaker and then the stick pusher activated but the captain may have believed that they were in a tail stall. He pulled hard and used considerable aileron to attempt recovery with discouraging results.

Two high tech glass cockpit airplanes with professional crews somehow fell victim to basic aerodynamics. In the case of the Airbus 330 in the AF 447 accident, three airspeed probes apparently froze up, the computer got confused and handed the aircraft back to the pilots. There were some conflicting indications but in the calm of hindsight it could be said that had they merely gone with pitch and power indications everything would have remained manageable. That will come out in the final report. A totally separate question is why three separate probes took a powder at the same time.

Now step back into the low tech world where the Air Safety Institute’s Piper Archer has been equipped with a state of the art Angle of Attack (AOA) system by Alpha Systems. In last week’s blog we discussed my flight review with stalls, slow flight and multiple landings. To be sure,there is a huge difference between the Archer at low altitude and the “Bus” at high altitude but  the concept is essentially the same.

The Archer’s AOA which is mounted next to the windshield post, was a confidence builder in helping to fly the Archer more precisely and slowly. It was calibrated at stall or alpha floor as the jet types like to call it. Too fast and there is an upward pointing yellow arrow, exactly in the groove and just above stall, there’s a green doughnut and too slow will yield a red downward pointing arrow and a voice reminder that you’re too slow. There’s also a warning warble when alpha moves into the yellow arrow range.

Airspeed is an approximation of alpha and the numbers change depending on aircraft weight and wing loading in turns. Wouldn’t it be better to teach from the beginning with alpha awareness? I think so, but it’s never caught on with the light aircraft crowd. Apparently, it’s beginning to be an issue with the big iron folks. Navy pilots are taught AOA right from the beginning and they operate from some really short floating airstrips.

Using Alpha, I consistently flew the Archer 5 knots slower on short final—which translated into better landings, less float, less tire wear and one of the best spot landings in memory. I should have bet some adult beverage on that but it just garnered a “nicely done.”

Bruce Landsberg
President, AOPA Foundation

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15 Responses to “Quit stalling – please!”

  1. Anonymous Says:

    Although it is true that the outcome of both these disasters most immediately stemmed from improper flight control inputs, the contributing factors (being unfit for duty in the case of Colgan & erroneous flight instrument displays for the former) appear to be more at fault than the pilots’ capabilities. Moreover, both of the aircraft in question are equipped with some variation of a pitch limit indicator to show proximity to the critical angle of attack. Essentially both flight crews suffered from information overload leading to a misdiagnosis and ultimately incorrect reaction to their respective situations. Adding yet another – and somewhat redundant – piece of information to an already cluttered PFD could potentially be to the detriment of yet another experienced and qualified flight crew.

  2. Steve K Says:

    It is my understanding the flight crew of the Air France flight only had about 3-4 minutes from autopilot disengagement till the aircraft pancaked on the ocean… considering there was a cascade of failures blaring in the dead of the night in bad weather over open water, Im not sure how I would do either with such a large aircraft in a flat free fall…

  3. LUIS A GUEVARA Says:

    Too much automation perhaps? Basic Attitude Instrument flying should be enough as it was enough in the times of Lindbergh.

    However if the airplane has already entered the “coffin corner” where lowering the nose will make your wing supersonic, will not resolve a stall that should have never happened.

    The retirement of Baby Boomers from the airlines left the planes in the hands of people that have never seen a Gyro.

  4. Johnny White Says:

    AOA is what it is all about if you as a pilot want to stall or not. An AOA instrument in the cockpit would be a better one than some that are installed but all airplanes have an AOA indicator already! It is the yoke or stick.
    For a given weight and CG the airplane will stall at the same stick position either positive or negative load at the same position regardless of speed or attitude.
    The piticular AOA instrument you flew with is not a true AOA system but a Stall Margin Indicator. Works pretty much the same but no for negative Or zero G.

  5. Jim Aukes Says:

    Bruce,
    How was this AOA system installed on this aircraft?
    I respect that your article is about safety, when a unapproved system is installed in a certified aircraft is this safe?
    I have looked into this system and find no way to install this into a certified aircraft. This system does not have any FAA, PMA, or STC approval.
    Is this really safe?

  6. Bruce Landsberg Says:

    Jim…

    Let me defer to our resident expert on the project and advise. My understanding is that we are in compliance with all applicable rules that apply to CAR3 aircraft. Stand by for an answer and thanks for asking.

  7. JJ Greenway Says:

    Actually, the system is quite legally installed. It’s an approved system and the considered a “minor alteration”.

  8. Herb Ludgewait Says:

    Stop teaching pitch to altitude. Problem solved!

  9. Pranesh Dey Says:

    I believe the same guys who stalled 447 wouldn’t have done the same mistake in a light aircraft, with or without an AOA. What was it that overwhelmed the FP in 447 — lack of manual hanlding for a long time (that too at a high altitude where the aerodynamics are different), automation reliance, in a procedure-driven profession the absence of a procedure for the situation A447 found itself in? Since an airline’s procedures do not take into account each pilots’
    individual weaknesses and strengths, all pilot must have his own personal checklist that appreciates his/her limitations and he/she remains prepared for them all the time. Even that old adage is good enough: aviate, navigate, communicate. He/she must appreciate that up there he/she is all alone.

  10. grumpy Says:

    Bruce, please don’t tell us you’re gazing at your panel on short final. 5 knots? Seriously?

  11. Bruce Landsberg Says:

    Grumpy….

    Better that than my navel!!!

    Kidding aside, this was an exercise in max performance both for me and the aircraft. The nice thing about this installation is that it can be seen in peripheral vision as you’re looking out the front. The audio warning serves as an attentive co-pilot so I felt that I was focused on the main event.

    The AOA makes it pretty easy to make consistent on-speed approaches – something that invariably precedes a good landing.

  12. Charles W. Carr Says:

    There are is a long list of things in what I’ve read about AF447 that are hard to believe. How can a pilot who understands the relationship between pitch, power and airspeed stall an airplane which has lost the airspeed indication? What happened to the ground speed data? How can a pilot sit at the controls and watch an attitude indicator with over 30 degrees nose up and vertical speed at 10000 fpm down and not know the wing is stalled. Why would you design a flight control system to keep you within the flight envelope and provide no guidance when you’re outside the envelope? I understand why the auto throttle disengaged on loss of airspeed input but why the autopilot? AOA would be helpful in this case but attitude instrument flying basics would prevent the stall. Personally, I believe the full story is not being told. When it is there should be a lot to learn about training and system design.

  13. Jack Voss Says:

    Getting back to GA from major airlines – it seems to me (still a student pilot) that angle of attack is so critical that it should be both indicated and taught as a major part of basic air skills.

    I’m having an AOA indicator installed in my 172 in a couple of days, and expect to be less in doubt about how close I am really flying to the edge of control. If it helps to keep me alive and helps me to fly a bit better, that somehow seems to be moving in a good direction. But, I’m only a student.

  14. Zagorfly Says:

    Af 448:
    1) more radar weather training
    2) mandatory departure delay to clear weather
    3) emergency tail drag schute deployed automatically in stall conditions and jettisoned a soon aoa is within the flying envelope.
    4) more training in manual handling at high cruise elevation

    Regards

  15. Harold Zamora Says:

    Just what Instruments did they have to provide attitude( Pitch & Roll) info?
    What happens to the Elevator & Stab when the Joy stick is not in the neutral position?

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