Asymmetric flap failure

[leading edge!]

Folks,

I recently listened to a UK controller at my local airfield describe how a Cessna taxied out to the thresold with one flap up and the other fully down. As we know these lessons would bite us hard and it was only an alert controller who spotted this, who averted a very big moment. The instructor who was in the aircraft missed this defect and was nearly ready for departure. I chuckled as I thought, I will learn from that and never let that happen to me!

As a result, I have been careful to ensure that my students ensure that flaps are operating symmetrically in checks on the ground.

Well, imagine my shock at the following?!?! Myself and an experienced airline captain (my student) were landing at an airfield two weeks ago in an HR100.

The base leg was flown normally though flap was deployed a little late. Flaps were within flap limiting speeds. We turned onto finals at which point full flap was deployed. At about 700' agl, 6th sense kicked in, but I detected a small 'clicking' noise coming from the left flap. I made a symmetrical check (which I always now do!) to find that there was a significant variation between left and right flap.

Our power setting was relatively low, but I was aware that my student was now beginning to apply aileron to counteract this inbalance. I immediately opted to continue approach as I raised flaps and called 'go around'.

The rest of the flight was uneventful and we flew a flapless circuit and landed. Enquiries are ongoing with the defect.

The big thing for me was learning from experience.. I cannot thank this individual from my tower enough. I am in little doubt, that during my instructors course (despite being thorough) there was mention of this type of incident apart from a downwind to base considerations....

Please let this be a lesson. I suspect that if we had applied full power, the roll rate would have been highly entertaining to say the least! With a load of airflow over those flaps, it would have made a significant problem with handling. I love aeros, but not close to the ground!

The incident has been reported, but please take note! I suspect that this could happen to various a/c types...

Leading Edge!

[Pilot DAR]

Interesting event, and certainly a good one to learn from.

If you have access to a Piper Navajo flight manual, there are sections on this subject. Both the Navajo, and Twin Comanche seem vulnerable to this because of the design of the flap system. The very high time Navajo pilot who gave me a checkout once, told me that he had landed a Navajo with near zero flap one side, and near full the other. it worked, but took full aileron, and the crosswind from the "helping" side.

Though not wishing to second guess as successful outcome, (and certainly not giving instruction) I have been taught from several different sources, that if you have had a flap failure, you're best to leave the flaps alone if the aircraft is controllable, and land it as is. Only an uncontrollable aircraft should have the flaps reselected, and then only with great caution, lest it get worse.

In my early days flying Piper Aztecs, we departed to find that we had a difficult to control roll at cruise speed, which was hardly noticeable at slower speeds. After some head scratching, it was found that there was about 2 inches (spanwise) for flap trailing edge which had been bent up hanger rash style. there was enough free play in the flap that at cruise speed, that new "trim tab" would fly the flap up, and through the whole plane out of roll trim. Easy fix.

Sometime later, I was doing practice touch and goes in a C 180 floatplane. Land with 40, apply power, retract to 20 on the step, and go. Upon retracting to 20, the flap lever "felt funny". I took off with the 20 (permissible on that type). Once airborne, I could not move the flaps at all. I flew home and landed. As I taxied in to the dock, there were some surprised expressions on shore, as the inboard end of the right flap (not at all easily seen from the left seat) was hanging down - the track had separated form the wing spar. Though I had not had asymmetric flaps, I had been very close!

[Genghis the Engineer]

Interesting.

I've never had an asymmetric flap failure (a couple of symmetric ones in a C150 and an AA5), but whenever I've run the certification programme on a single which had flaps, I've always insisted on a run through the design of the flap circuit and if there seems any reasonably high probability of an asymmetric flap failure have insisted that we test the aeroplane with asymmetric flaps to ensure adequate controllability.

The way we normally did it was to disconnect flaps on one side, get airborne and climb to a safe height flapless, then progressively select flaps - so we'd only get it on one side - then simulate typical manoeuvres including an approach and go-around.

I don't know if Piper and Cessna, for example, do the same thing?

G