History of Flight
On February 26, 2008, at 1645 eastern standard time, a Beech A36, registration N623CQ, was substantially damaged during a forced landing near Athens, Georgia. The certificated pilot and a pilot-rated passenger, who were the aircraft owners, reported no injuries. Visual meteorological conditions prevailed, and an instrument flight rules (IFR) flight plan was filed for the personal flight conducted under 14 CFR Part 91. The airplane departed Gwinnett County Airport (LZU) in Lawrenceville, Georgia, destined for Charlotte-Douglas International Airport (CLT) in Charlotte, North Carolina.
According to the pilots, prior to the flight, an annual inspection had been completed and a newly overhauled propeller installed. They performed a preflight inspection, engine run-up, and high-speed taxi checks before takeoff.
The pilot-rated passenger stated that he wanted to fly with the pilot, his new co-owner, because the pilot had just completed training for the A36. After leveling at 7,000 feet, they discussed engine management and noticed high propeller rpm. They decided to divert to Athens and notified air traffic control. The propeller was adjusted but continued to overspeed. The pilot-rated passenger managed engine and propeller rpm while the pilot flew, 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 below the clouds, the pilot selected a field for a forced landing because 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 ratings for airplane single-engine land and instrument airplane, and an FAA third-class medical certificate issued in April 2006. He reported about 417 total flight hours, with 48 hours in the accident make and model.
The co-owner/pilot-rated passenger held a commercial pilot certificate with ratings for airplane single-engine land and instrument airplane, and an FAA third-class medical certificate issued in August 2006. He reported 1,736 total flight hours, including 1,207 hours in the accident make and model.
Aircraft Information
According to FAA records, the airplane was a 1978 Beech A36 with 7,588 total aircraft hours. The last annual inspection was performed on February 24, 2008, at 7,588 hours, and the accident flight was the first after that inspection.
Meteorological Information
At 1558, weather reported at Athens-Ben Epps Airport (AHN), located 6 miles northeast, included a broken cloud layer at 2,800 feet and an overcast layer at 3,700 feet. Winds were from 280 degrees at 17 knots, gusting to 28 knots. Temperature was 6°C, dew point 3°C.
Wreckage and Impact Information
Photographs of the wreckage showed the airplane mostly intact, with damage limited to 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 FAA supervision. The Hartzell representative reported that the rear pitch change rod bushing had 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, normally dry, contained significant amounts of oil. The bushing showed traces of sealant, but 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, creating a fixed pitch condition. Engineers determined that an airspeed of 97 knots or slower would be required to produce positive thrust from the propeller system under the as-found condition. The pilot reported maintaining the airplane manufacturer's recommended best-glide speed of 110 knots throughout the descent.
Following the investigation, Hartzell Propeller, Inc., published Revision 31 to Standard Practices Manual No. 202A, Volume 3, Aluminum Hub Overhaul, in December 2008. The revision outlined inspection and repair criteria and modified the pitch change rod bushing installation, requiring 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."