AD 56-17-02

56-17-02 de HAVILLAND: Applies to All Model DHC-3 Otter Aircraft.

Compliance required as indicated.

The Canadian Department of Transport has issued the following directive with which the FAA concurs and considers mandatory.

"Any malfunctioning of the flap hydraulic circuit check valve would fail to lock the flaps in any flaps-extended position. When the valve operates properly, the flaps remain stationary when the flap selector lever is moved to the 'up' position and until the flap pump is operated. However, if the valve sticks open for any reason, selecting 'flaps up' results in a rapid flap retraction without use of the pump. Such retraction at high speeds will produce large stick forces and out-of-trim condition which flight tests have shown to be very dangerous when the aeroplane is trimmed for a high flaps-extended speed (full aircraft nosedown trim).

"Therefore, until modifications now under development are incorporated, the following restriction is mandatory:

"(a) The flap selector must not be placed in the up position until it is desired to retract the flaps, nor at speeds in excess of the following:

Flap Setting Maximum Trim Speed Landing (35 degrees) 65 mph IAS Takeoff (30 degrees) 75 mph IAS Climb (15 degrees) 85 mph IAS

"The previous '15 degrees climb flap limitation' on the use of flaps is canceled and the special 50- hour inspection of the flap controls, etc., may be discontinued."

Incorporation of de Havilland Modifications 3/731, 3/744 and 3/745 is required by November 1, 1957, as outlined in D.H. Engineering Bulletin Series "O" No. 34, dated January 21, 1957. When these Modifications are incorporated, the operating restrictions in section (a) above will no longer be required.