Aviation Safety Newsletter - Volume 2, No. 2

Submitted by on Wed, 01.08.2007 - 00:00

Wing Flap Failures

by Roger M. Delisle

The topic for this issue of the Newsletter is based on an incident which I experienced and would like to share with you, not unlike the first-person accounts of such famous magazine columns as Flying’s “I Learned about Flying from That”, or AOPA Pilot’s “Never Again”.  The spirit of these popular regular features, which I highly recommend, is for pilots to put safety before personal pride by sharing their personal experiences with readers so that mistakes shouldn’t needlessly be repeated.  Do keep in mind, however, that normally, the Safety Committee keeps the identity of persons involved in an incident completely confidential, so you should feel free to report occurrences without having to turn them into public confessions.

What Happened?

I was alone in a rental Cessna Skyhawk at Rockcliffe on a calm, sunny, late afternoon in May of 2006.  After 3 normal circuits on runway 09, I turned on final once more, this time with 30 degrees of flaps, which I kept for the entire approach.  Without delay after a normal touchdown, I followed with the usual drill: Flaps up (I was flying an N model with a positional flap lever, not the toggle switch of earlier models), full throttle, carb heat off.  To my great surprise, I became immediately airborne again and with a nose-up attitude that needed instant correction to maintain airspeed above stall.  This was my very first reflex and, while still startled from the aircraft’s unusual behaviour, my goal was to maintain at least 70 knots while trying to figure out what was wrong.  Thinking I simply had forgotten to raise the flaps, I checked the lever but found it correctly set at 0 degrees.  It’s then that I glanced out the right window, noticed the flaps down at a steep angle and understood the failure.  Meanwhile, in those very short few moments, the 70-knot airspeed I had attained wasn’t giving me any climb performance so I gently raised the nose, which was much lower than usual, to let a climb of 60 knots take me very slowly upwards in a circuit for landing.  During the downwind leg, I had time to exclude both a general electrical failure (the radios were still working) and an open circuit breaker (they were all normal).  I also didn’t dare touch the flap lever, thinking I could make a bad situation even worse, so I completed the circuit with what appeared to be the 30 degrees of flap I had set for my previous landing.  I landed normally and taxied back to the ramp, leaving everything untouched at shutdown to show the failure and possibly preserve any evidence of its cause.

The next day, after maintenance thoroughly checked the aircraft and returned it to service, there had been no findings as to the cause of the failure.  This leaves me nothing but speculation: Was it an electrical contact failure of the flap lever, perhaps because I was too abrupt when raising it to the 0 degree position? Quite possibly.

This failure could have gone much worse for me had there been other aggravating circumstances that would have brought my climb rate from poor to nil, for example flying at gross weight on a hot day, or in a C150 with an instructor, with 40 degrees of flaps extended instead of only 30.  In fact, this is precisely why for several years now, Cessna has limited the flap extension of all their newly-manufactured C172’s to 30 degrees.  This shows how seriously the issue has been treated, and therefore how pilots of older models need to manage the risk of flap failure accordingly.

What Could I Have Done Differently?

Well, for one thing, I learned on that day what my ab initio training of nearly 20 years ago did not teach me, and which my re-currency training somehow didn’t catch:  A touch-and-go procedure should always include checking the flaps to ensure their retraction.  In the case of the C172’s electrical flaps, the time it would take to see them fully retract would be too long on the rollout and would eat up too much remaining runway for a safe takeoff afterwards, so seeing them moving up from 30 degrees or less on both wings is a good compromise that ensures we’ll climb on takeoff.  For other aircraft types, acceptably safe flap settings for initial climb need to be determined and applied by visual check.  For the C172, the touch-and-go procedure is:

  • Touchdown & maintain directional control;
  • Select flaps up;
  • Check the left flap for retracting motion, then look ahead for directional control;
  • Check the right flap for retracting motion, then look ahead for directional control;
  • Are both flaps retracting? 
    • Yes: Apply power for takeoff and set the carb heat to Cold. We’re going flying.
    • No: Reject the takeoff.

I would have been much better with a rejected takeoff than the harrowing circuit I flew at the time.  I have to say that to this day, I have never seen another pilot check over their shoulders for flap retraction, and I have to wonder who does… So far, it has earned me some praise from an instructor while on a dual check ride some time afterwards…But are all instructors enforcing this?  Is it part of your procedure?

Failures During Flight

The only phase of flight where a flap failure poses a significant problem is during a missed approach, where the flap extension can be greater than that designed for climbing.  This is where our Chief Flight Instructor Simon Garrett kindly arranged a short demonstration flight with me to illustrate the performance limitations of a full-flap climb and the options available when a failure compels a pilot into that scenario.

On a balmy late afternoon earlier this summer, Simon and I took off in a C172N from runway 09.  The first circuit brought us to a simulated power failure, a good exercise which, this time, doubled as a good way to set up a 40º flap approach.  Then on the overshoot1, we kept the flaps down while applying full power.  Amidst the constant buffeting, the climb rate was very poor and frequently below 200 ft/min. at 60 knots. I was suddenly reliving last year’s failure, albeit in safer settings, and in slightly worse performance conditions than those at the time, given an extra person on board and the full 40º flaps versus 30º.

“What are your options?” asked Simon. The strategy is to keep it simple. If I can climb safely away from terrain and obstacles, I will abbreviate the circuit and return for a landing.  If not, I will look for the most suitable landing site with as few and shallow turns as possible. Once around the circuit for a full-flap approach and landing, there is another precaution to remember:  At full flaps, the Skyhawk’s pitch while in climb or cruise configuration will be very different from its usual nose-down attitude during approaches and landings.  So whenever flying with substantial power and flaps, to avoid a sudden loss of airspeed, reduce power incrementally and re-trim each time to ensure good airspeed control all the way to the approach configuration.

So in short, the decision on the best course of action depends on whether or not you can climb at a sufficient rate to clear all obstacles safely. In that case, a continued flight around the circuit to return for a landing is best.  If unable to maintain altitude, an off-airport landing is likely the best option.

Asymmetric Failure

This is when only one flap fails to move either down or up, while the other travels normally to the new position selected in the cockpit.  It is by far more dangerous than the symmetric failure described so far, but also much rarer. Electric flaps use a single actuation mechanism wherever possible.  In the 172, the design incorporates one electric motor turning a single jack screw which deploys both flaps. For only one flap to fail would mean bending or breakage of the linkages tying them together, which isn’t very likely.  If it does occur during touch and go cycles, the on-ground 2-way check in the procedure described above would cover that possibility with a takeoff rejection.  At any other time during flight, however, an asymmetric failure may result in an immediate roll and loss of control with fatal consequences if not corrected immediately.  In some cases, an aircraft can maintain control with asymmetric flaps if the speed is reduced and full aileron deflection is used.  Regardless of the phase of flight, whether raising or lowering flaps, if an asymmetric failure is suspected, the immediate reaction should be to return the flap selector to its position at the time immediately preceding the upset, and adjust it from there if needed.  The goal is to return the working flap to the same position as the failed flap, in an attempt at restoring symmetry to the flying surfaces, then to deal with the failure as described above.

Closing Remarks

Overall, I found the personal experience of an actual in-flight anomaly to be an invaluable lesson, in both a lost feeling of invulnerability as a pilot and in how the most entrenched procedures, ones we often take for granted, are not beyond correction and refinement in light of what accidents and incidents can teach us.  As always, I welcome comments and questions by e-mail.

Roger Delisle This email address is being protected from spambots. You need JavaScript enabled to view it..

1 For the demonstration flight, we overshot the runway from an altitude of approximately 500 ft  to ensure a sufficient margin of safety.

Disclaimer:  The sole purpose of this Safety Newsletter article is to educate pilots and other persons involved in aircraft operations, strictly in the interest of promoting flight safety.  It is not intended as a substitute for any official investigative report which may or may not exist relating to any incident mentioned. In no way should it be interpreted as apportioning civil or criminal responsibility on any party, including, but not limited to, manufacturers, suppliers, operators, pilots, air crew, maintenance personnel or governmental authorities.