SEA95LA160
SEA95LA160

On July 23, 1995, approximately 1520 Pacific daylight time, a Cessna 172, N8627B, received substantial damage in a collision with terrain following a loss of control at low altitude on initial climbout from Lost River Airport, 5 miles northwest of Mazama, Washington. The private pilot, who owned the airplane and was its sole occupant, was not injured. The 14 CFR 91 flight was bound for Corvallis, Oregon. Visual meteorological conditions existed and no flight plan had been filed.

The pilot stated the following in his report of the accident:

The wind was directly down [the] runway. Using '29' with headwind I took off with 20 [degrees] of flaps. As I reached the top of the trees my right wing dropped and was pointing at the ground. [It] was as if I lost lift on [the] right wing...I used ailerons to try to counter the dropped wing - help[ed] some but right wing would not stay up - there was 'no' stall warning at any time - I was coming back down like a floating leaf and the right [wing] caught the runway first - cartwheeling me to the left wing and then the nose in full throttle.

According to the U. S. Government Airport/Facility Directory, runway 29 is a 3,150 by 85 foot turf and gravel runway at an elevation of 2,415 feet above sea level. The pilot stated in a phone interview with the investigator that he had been concerned about terrain clearance over a ridge off the end of runway 29, and that the use of 20 degrees of flaps was a technique he had previously been taught to use to deal with this situation.

Two witnesses, who were friends of the pilot, watched the pilot take off and witnessed the accident. These witnesses, who stated that they observed the accident from mid-field, furnished a jointly signed statement which read as follows:

Aircraft did normal runup and began takeoff roll on runway 29 with what appeared to be 20 [degree] flaps deployment. Wind was 15 to 20 [knots] from 270 [degrees]. Runway has trees on both sides. Aircraft rotated and initiated a healthy rate of climb....Aircraft reached tree top level and right wing dropped. Aircraft then stalled and broke to the right impacting approx[imately] 1,000 [feet] from beginning of [takeoff] roll. Post impact inspection found flaps to be completely retracted and wing damaged to the point they could not be deployed.

I distinctly saw flaps deployed during climb.

The airplane is equipped with mechanically actuated flaps. In his report, the pilot expressed a belief that the flaps had inadvertently retracted during the climb and had thereby induced a stall. He stated in his report: "after all was over the flaps were at '0' [degrees] and fully retracted." He further stated in his report that he had had two previous problems with the airplane's flaps in the past year. His report stated: "One flap mounting bracket broke on a landing (repaired-different left flap installed) and on 5-27-95 the flap lever would not lock in on landing. Repair done at Corvallis FBO...." The pilot furnished copies from the aircraft logbook documenting these jobs. To verify the report of flap problems, an FAA inspector from Spokane, Washington performed an inspection of the aircraft wreckage at Aircraft Salvage & Rebuild, Inc., Omak, Washington. Her report stated the following:

Removed access panel to floor mounted flap actuation handle. Found cables attached. Slots in the assembly were not worn or found to be of any concern. Flap handle moved freely [and] normally and locked at each flap setting position normally.

Salvage personnel stated at time of recovery, flap handle was down [and] flaps were at -0- setting. They also stated that at disassembly, the flap cables were attached.

At the time of our inspection, both wings were removed from the aircraft.

Photos taken by the aircraft salvage crew at the time of wreckage recovery, and supplied to the investigator, showed the flaps in a slightly extended position estimated at approximately 10 degrees down.

An Aircraft Salvage & Rebuild mechanic checked the airplane's stall warning system in support of the investigation. According to the 1957 Cessna 172 owner's manual, the stall warning horn "is adjusted to give an audible warning approximately 5 mph above the normal straight ahead stalling speed. Other attitudes and speeds provide a wider margin." The mechanic's report stated: "...[The stall warning horn] worked as normal. The detector in the [right] wing worked normally using a VOM to check continuity. There didn't appear to be any sticking or binding of the detector."

The owner's manual for the 1957 Cessna 172 notes that the flaps "supply added lift and considerable drag", and specifies the following procedures for takeoff and climb:

"TAKE-OFF. Normal and obstacle clearance takeoffs are performed with flaps retracted. The use of 10 [degrees] flaps will shorten the ground run approximately 10%, but this advantage is lost in the climb to a 50 foot obstacle....Flap deflections of 30 [degrees] and 40 [degrees] are not recommended at any time for take-off."

"CLIMB. ...If an obstruction dictates the use of a steep climb angle, the best angle-of-climb speed should be used with flaps up and full throttle. These speeds vary from 56 m.p.h. at sea level to 63 m.p.h. at 10,000 feet."

The power-off stalling speed chart in the owner's manual gives the flaps-up, wings-level stall speed as 58 mph and the 10- degree-flap stall speed as 56 mph. The chart indicates power-off stall speeds at a gross weight of 2,200 pounds.

The airport is located in a river valley in mountainous territory, with terrain rising to 8,726 feet above sea level (6,311 feet above the airport elevation) approximately 5 nautical miles north-northwest of the airport. The river valley and runway are oriented northwest/southeast, with another valley joining from the north immediately beyond the departure end of runway 29. FAA Advisory Circular (AC) 61-23B, "Pilot's Handbook of Aeronautical Knowledge", states: "Between hills or mountains, where there is a canyon or narrow valley, the wind will generally veer from its normal course and flow through the passage with increased velocity and turbulence. A pilot flying over such terrain needs to be alert for wind shifts...." FAA AC 00-6A, "Aviation Weather", also states: "The airport area is especially vulnerable to mechanical turbulence which invariably causes gusty surface winds. When an aircraft is in...a climb, airspeed fluctuates in the gusts, and the aircraft may even stall." The pilot estimated wind at the accident site as being from 290 degrees at 25 knots, gusting to 35 knots. Both the pilot and the witnesses reported that the airplane's right wing initially dropped when the airplane reached the tops of the trees surrounding the airport.

The airplane was equipped with a retrofitted shoulder harness. The pilot expressed a strong opinion to the NTSB investigator that the shoulder harness had spared him from injury or death in the accident.

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