C172. Flap asymmetry?

[Pilot DAR]

I am told by an aircraft engineer and designer that for Australian certification, which is based on FAA, an aircraft must be able to demonstrate that the ailerons can maintain control with one flap up and one fully down.

Not correct. The FAA design requirement closest to this is:

Sec. 23.143

General.

(a) The airplane must be safely controllable and maneuverable during --
(1) Takeoff;
(2) Climb;
(3) Level flight;
(4) Dive; and
(5) Landing (power on and power off).
(b) It must be possible to make a smooth transition from one flight condition to another (including turns and slips) without exceptional piloting skill, alertness, or strength, and without danger of exceeding the limit load factor, under any probable operating condition (including, for multiengine airplanes, those conditions normally encountered in the sudden failure of any engine).
(c) If marginal conditions exist with regard to required pilot strength, the "strength of pilots" limits must be shown by quantitative tests. In no case may the limits exceed those prescribed in the following table:

Values in pounds of force as applied to the control wheel or rudder pedalsPitchRollYaw

(a) For temporary application:Stick---------------------------------------------

6030--------------------------

Wheel (applied to rim)-------------------

7560--------------------------

Rudder Pedal-------------------------------

----------------------------------------------------150

(b) For prolonged application.

10520

No mention of asymmetric flaps.

At least one type I have flight tested specifies adjusting a flap to trim out a roll force. The amount of flap displacement to really affect roll trim is about 1/8" at one flap trailing edge. Can you imagine the roll trim effect of one up and one down? If the flaps are effective, any significant asymmetry will overpower a pilot.

If it was unsafe to operate the flaps during a turn it would say so in the "limitations" section of the POH.

Very true.