Cessna 177 N3487T accident near St. Johns, Arizona

Probable cause

The failure of both pilots to abort the takeoff when a suitable climb rate could not be attained. Contributing to the accident was the reduction of available power due to the camshaft lobe and lifter corrosion/wear, the high density altitude, and the CFI’s inadequate supervision.

NTSB analysis

The certified flight instructor (CFI), pilot undergoing instruction (PUI), and one passenger were departing from an airport with a density altitude of 8,690 feet mean sea level. The fuel tanks were filled to maximum capacity, and the estimated gross weight was about 130 pounds less than the maximum gross weight. During the takeoff, a witness at the airport observed that as the airplane traveled down the runway there was no change in engine sound. The witness further stated that as the airplane lifted out of ground effect , it did not climb any higher. It continued down the runway and at its end, the witness saw the airplane stall and turn to the left, prior to ground impact. The PUI reported that during the takeoff, “We used virtually the entire runway for takeoff.” The PUI was focused on obstacles ahead of the runway and notified the CFI that they had cleared the obstacles. The PUI indicated that the CFI then assumed control of the airplane and entered the airplane into a climb to clear additional obstacles. The PUI stated that as the flight controls were pulled back it felt like they had less available power, most likely due to the attitude of the airplane. The airplane then collided with obstacles. Post accident engine examination showed that the intake lifter for the Number 4 cylinder camshaft lobe was worn and the follower was heavily pitted. Both the intake and exhaust lifter for the Number 3 cylinder were heavily scored and the corresponding camshaft lobes were heavily worn. While the exact amount of degradation to the engine's power output could not be established, the alteration of the cam lobe profile will alter the amount and duration of the valve opening, thus affecting power output. The engine was overhauled 10 years prior to the accident and had accrued about 330 hours during this time. Although the engine's storage history for the last 10 years could not be determined, the amount of corrosion and pitting found make it highly likely that the internal engine components corroded due to inadequate lubrication resulting from lack of consistent operation. Lycoming Service Letter L180B states that, "Engines in aircraft that are flown only occasionally may not achieve normal service life because of corrosion." A Lycoming publication states that, “Corrosion is a known cause of tappet and cam lobe wear. The engines of aircraft that are not flown regularly may be extremely vulnerable to corrosion...Once started, the process is not likely to stop until it reaches a point where these parts are doing an unacceptable job.”

Text from the NTSB. Open the NTSB docket for SEA08LA179 for the full record.