Athens, GA, USA
N623CQ
BEECH A36
After takeoff on the first flight following a propeller overhaul, the airplane was leveled at 7,000 feet, and as the pilot and pilot-rated passenger discussed engine management, they noted the propeller rpm was high. They diverted to an alternate destination, and notified air traffic control (ATC). The propeller was adjusted but continued to overspeed. The pilot rated passenger managed engine and propeller rpm while the pilot flew the airplane at the manufacturer's best glide speed of 110 knots, but the engine continued to overspeed as the propeller provided no thrust. As propeller thrust and altitude decayed, the airplane descended through a cloud layer. When the airplane broke out beneath the cloud layer, the pilot selected a field for a forced landing area due to the fact that the surrounding terrain was wooded. Upon touchdown, the airplane bounced, the nose gear collapsed, and the airplane skidded to a stop. The pilot and pilot rated passenger stated that prior to the accident flight an annual inspection was completed and a newly overhauled propeller was installed. Disassembly of the propeller system after the accident revealed the rear pitch change rod bushing separated from the rear hub half and became loose in the hub. The bushing displayed traces of bonding sealant; however, the hub bore for the bushing did not. The hub cavity and the area on the aft side of the propeller piston, which are normally dry, contained "significant" amounts of oil. Pressurized oil on both sides of the propeller piston resulted in a hydraulic lock, fixed pitch condition. Using the as-found condition of the accident propeller system, engineers determined that airspeed of 97 knots or slower would be required to create positive thrust from the propeller system. After the accident, the propeller manufacturer revised its inspection and repair criteria, and changed the pitch change rod bushing installation procedure from one that used bonding sealants, to one that required a spiral retaining ring. The use of bonding sealants was no longer permitted.
HISTORY OF FLIGHT On February 26, 2008, at 1645 eastern standard time, a Beech A36, N623CQ, was substantially damaged following a forced landing near Athens, Georgia. The certificated pilot and pilot rated passenger, the aircraft owners, were not injured. Visual meteorological conditions prevailed and an instrument flight rules (IFR) flight plan was filed for the personal flight conducted under the provisions of 14 Code of Federal Regulations Part 91. The airplane departed Gwinnett County Airport (LZU), Lawrenceville, Georgia, and was destined for Charlotte-Douglas International Airport (CLT), Charlotte, North Carolina. The pilot and pilot rated passenger stated that prior to the accident flight an annual inspection was completed and a newly overhauled propeller was installed. The pilots completed a preflight inspection, engine run-up, and high-speed taxi checks prior to takeoff. According to the pilot rated passenger, he wanted to fly with the pilot, his new co-owner, because the pilot had just completed training for the A36. The airplane was leveled at 7,000 feet and as they discussed engine management, they noted the propeller rpm was high. They decided to divert to Athens, Georgia, and notified air traffic control (ATC). The propeller was adjusted but continued to overspeed. The pilot rated passenger managed engine and propeller rpm while the pilot flew the airplane, but the engine continued to overspeed as the propeller provided no thrust. As propeller thrust and altitude decayed, the airplane descended through a cloud layer. When the airplane broke out beneath the cloud layer, the pilot selected a field for a forced landing area due to the fact that the surrounding terrain was wooded. Upon touchdown, the airplane bounced, the nose gear collapsed, and the airplane skidded to a stop. PERSONNEL INFORMATION The pilot held a private pilot certificate with a rating for airplane single engine land and instrument airplane. He held a Federal Aviation Administration (FAA) third-class medical certificate which was issued in April 2006. The pilot reported approximately 417 total hours of flight experience, of which 48 hours were in make and model. The co-owner/pilot rated passenger reported he held a commercial pilot certificate with ratings for airplane single engine land and instrument airplane. He was issued an FAA third-class medical certificate in August 2006, and he reported 1,736 hours of total flight experience with 1,207 hours in make and model. AIRCRAFT INFORMATION According to FAA records, the airplane was a 1978 Beech A36. The airplane had accrued 7,588 aircraft hours. The owners reported the last annual inspection was performed on February 24, 2008, at 7,588 aircraft hours. The accident flight was the first after completion of the annual inspection. METEOROLOGICAL INFORMATION At 1558, the weather reported at AHN, 6 miles northeast, included a broken cloud layer at 2,800 feet with an overcast layer at 3,700 feet. The winds were from 280 degrees at 17 knots gusting to 28 knots. The temperature was 6 degrees Celsius, and the dew point was 3 degrees Celsius. WRECKAGE AND IMPACT INFORMATION Examination of photographs of the wreckage revealed that the airplane appeared mostly intact. The damage was limited to the separation of the nose landing gear, and buckling of the forward cowling. TESTS AND RESEARCH A detailed examination and disassembly of the propeller system was performed by a representative of Hartzell Propeller, Inc., on March 28, 2008, under the supervision of an FAA inspector. According to the Hartzell representative, disassembly of the propeller system revealed the rear pitch change rod bushing separated from the rear hub half and was loose in the hub. The hub cavity and the area on the aft side of the propeller piston, which are normally dry, contained "significant" amounts of oil. The bushing displayed traces of sealant, however, the hub bore for the bushing did not. Locquic and Loctite sealants were prescribed for both the bushing and the bore. The Hartzell representative stated that pressurized oil on both sides of the propeller piston resulted in a hydraulic lock, a fixed pitch condition. Using the as-found condition of the accident propeller system, Hartzell engineers determined that airspeed of 97 knots or slower would be required to create positive thrust from the propeller system. The pilot reported that the airplane manufacturer's recommended best-glide speed of 110 knots was maintained throughout the descent. As a result of the investigation, Hartzell Propeller, Inc., published Revision 31 to Standard Practices Manual No. 202A, Volume 3, Aluminum Hub Overhaul, in December 2008. The revision outlines inspection and repair criteria, and modified the pitch change rod bushing installation that required a spiral retaining ring instead of adhesive bonding. A caution states, "DO NOT INSTALL A BUSHING BONDED WITH ADHESIVE IN THE HUB. INSTALLING A BUSHING THAT USES AN INTERNAL SPIRAL RETAINING RING IS THE ONLY PROCEDURE PERMITTED."
The loss of propeller thrust due to the unseating of an internal propeller hub bushing. Contributing to the accident was the manufacturer's inadequate procedure to secure the bushing.
Source: NTSB Aviation Accident Database
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