Flaps won't extend beyond 2/3

[Ernie Martin]

A word of caution is that a flap setting beyond 2/3 MAY be dangerous.

There have been instances of a flap cable breaking on one wing and the aircraft rolling uncontrollably because of insufficient authority of opposite aileron when in full flaps. The problem may even occur at 2/3 flaps. Depending on altitude and how quickly you a) apply opposite aileron and b) raise the extended flap on one side, accidents have occurred and I believe there have been fatalities.

As a result, I adhere to several precautions. At annual inspections I give special attention to the flap-cable inspections. In flight I use more than 1/3 flaps only when absolutely necessary and I lower flaps at a higher altitude as a test, with my hand next to the flap lever to instantly raise the flaps if a cable breaks. So virtually all my landings are at 1/3 flap, where a quick calculation based on aileron and flap surface areas and moment arm indicated that 1/3 flaps on one side can be overcome with full opposite aileron.*

Ernie


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* I'm an aerospace engineer with an MS from Caltech.