NTSB Factual Report

On January 28, 2001, at 1541 Pacific standard time, a 1978 Cessna 182R, N7568T, registered to and operated by the Boeing Employees Flying Association, and being flown by a private pilot, incurred substantial damage during a gear collapse on landing at the Renton Municipal airport, Renton, Washington. The pilot and passenger were uninjured. Visual meteorological conditions existed, and no flight plan had been filed. The flight, which was personal, was operated under 14CFR91, and was on the last leg of a multiple stopover trip. The aircraft had last departed Olympia, Washington, approximately 1505.

The pilot reported in a telephonic interview, and subsequent written statement that: after departing Olympia there was a "...faint odor of electrical insulation abeam Tacoma, no anomalies found at that time...." Upon arrival in the Renton area the "...landing gear [was] extended while on 45 [degree] entry to downwind rwy 15. Pilot believed extension [was] normal, observed in position. Turned short final, approach normal. Pilot and passenger heard no gear up warning horn. Landing appeared normal until main gear began to fold up...."

Post crash examination immediately following the accident revealed that the nose landing gear was down and locked and both main gear were unlocked. The landing gear lever was in the "down" position, the amber "gear UP" light's iris was fully closed, the green "gear DOWN" light's iris was open 1/16 of an inch, and the landing gear motor circuit breaker was popped.

The aircraft was moved to a fixed base operator's (FBO) hangar on the field and placed on jacks, after which the landing gear system was checked and repeatedly cycled under the supervision of an FAA Inspector but without the characteristic air loads encountered in flight.* The first cycle revealed that the gear retracted normally with the exception that the electrically driven hydraulic pump continued to run after the landing gear was retracted. This condition was not duplicated upon repeated gear cycles. A calibrated pressure gauge was installed in the hydraulic system and the landing gear was cycled again with hydraulic pressures found to be within Cessna specifications. Additionally, the pressure switch was observed to open (shutting off the hydraulic pump motor) at 1,450 PSI, and to close (turning on the hydraulic pump motor) at 1,000 PSI (refer to ATTACHMENT PFM-I). The hydraulic power pack was removed from the aircraft and shipped to the FAA's Wichita FSDO, where under the supervision of another FAA inspector, the power pack was partially examined at the facilities of Aero Electric, Inc.; however, no meaningful findings were reported (refer to attached FAA/FBO documentation).

Further examination by the FBO revealed that the hydraulic power pack had worn gears within the pump assembly (refer to attached FAA/FBO documentation). According to a representative of the Cessna Aircraft Company, the pump assembly consisted of two steel gears within the pump housing, which was mounted atop the power pack assembly. The electrically driven gears provided the necessary hydraulic pressure to raise and lower the landing gear.

*The Cessna 182R's retractable landing gear are arranged such that the nose gear extends down and rotates aft on extension. During gear extension in flight, the nose gear is assisted into the down-and-locked position by air loads driving the nose gear aft. During retraction of the nose gear in flight the hydraulic pump has to overcome the air loads as it drives the nose gear up and forward. The main gear, which fold down and forward (opposite to the nose gear) during extension encounter reverse air load conditions during extension and retraction in flight.

NTSB Probable Cause

The worn condition of the hydraulic pump gears which resulted in a continuous running pump, subsequent pump motor overheat and eventually the tripping of the pump motor circuit breaker. An additional cause was the pilot's failure to verify that the landing gear were down and locked. A contributing factor was a partially blocked green annunciator light.