B737-400
Flight Crew Air Transport Pilot (ATP)
Distraction; Situational Awareness; Training / Qualification; Workload
Deviation - Speed All Types; Deviation / Discrepancy - Procedural Other / Unknown
Flight Crew Took Evasive Action; Flight Crew Became Reoriented; General Maintenance Action
Human Factors; Aircraft; Equipment / Tooling
We felt a buffet and found airspeed well into the barber pole. First Officer flying; I retarded the thrust levers to reduce speed. Our initial evaluation was we'd entered a mountain wave (165 KTS of wind at altitude); but the indicated speeds didn't make any sense. We started checking for other causes; pitot heat; etc. and found the flaps selected and indicating one (speed approximately 270 KIAS and at FL320). I retracted the flaps at approximately 235 KIAS; hand flew the airplane to check for roll or vibration and found all indications normal. We continued to our destination and landed without further event. We also limited descent speed as a precaution. What I believe happened: I was beginning to type a wind report to Dispatch when the autopilot trimmed the airplane. The trim wheel bumped my arm and I must have made contact with the flap handle enough to knock it out of the detent (reaching around the thrust levers and flaps to reach the keyboard). Approximately two or three minutes later the event occurred. If I bumped the flaps it was the result of being bumped by the trim wheel; and I had no idea anything had transpired. Just plain stupid bad luck; but it seems to me something that could be repeated and everyone should be aware of the possibility. Sure didn't know I touched the flap handle and they didn't come out immediately.
I would go so far as to say that I have seen every Captain I have flown with use this or similar move to send ACARS messages in the 400. It should be noted that newer airplanes do not have this potential problem because there is a menu button on both sides.
As a B737 Captain was entering ACARS data at FL320 he inadvertently moved the flap handle which caused airframe vibrations and a flap overspeed. When they recognized the error power was reduced and the flaps raised.