Grumman American Avn. Corp. AA 1B N4SU accident near Hawthorne, California

Probable cause

The failure of both pilots to land the airplane on the remaining runway when a sufficient rate of climb could not be attained. Contributing to the accident was a reduction of available engine power due to severe camshaft lobe wear.

NTSB analysis

The 90-year-old private pilot, who was the owner of the airplane, was receiving a flight review from the 71-year-old flight instructor. The airport tower controllers reported that, during takeoff, the airplane became airborne, settled back onto the 4,956-ft-long runway about 1,500 ft from its initial rotation point, and then become airborne again. The airplane remained low as it proceeded away from the airport. One witness reported that the engine sounded "rough" and that the airplane's rate of climb was "much lower" than that of a typical airplane on departure. The witness observed the pilot repeatedly lowering and raising the airplane's nose as if trying to gain altitude. Each time the airplane pitched up, it lost altitude, consistent with operation at or very near the airplane's critical angle of attack.

The airplane subsequently impacted a tree and a residence about 1 nautical mile west of the airport and was destroyed by a postcrash fire. Examination of the flight controls and airframe revealed no anomalies. Examination of the engine revealed continuity of the valvetrain and drivetrain; however, disassembly revealed radial scoring of the crankshaft bearings, spalling of the tappet faces corresponding to the intake valves of all 4 cylinders, and extensive wear of the corresponding camshaft lobes. The severely worn camshaft lobes would have reduced the amount and duration of the intake valve openings, resulting in decreased power output. The magnitude of the power loss could not be determined.

The airplane was operating within its weight and balance limitations, and, given the atmospheric conditions at the time of the accident, the takeoff distance should have been about 1,000 ft. When the airplane settled back onto the runway long after it should have become airborne, the pilots should have stopped the airplane and any further takeoff attempts; rather they chose to continue with a second takeoff and climb toward a densely-populated area.

The pilot purchased the 42-year-old airplane about 7 months before the accident. The most recent annual inspection was conducted about the time of the purchase at an airframe and engine total time of 1,724 hours. Although manufacturer guidance specified that the engine should be overhauled at 2,000-hour intervals or every 12 years, whichever occurred first, the engine had never been overhauled. The airplane had been operated less than 20 hours per year in the 2 years before the most recent annual inspection; according to the manufacturer, engines that are not operated on a regular basis may accumulate internal corrosion due to a loss of protective oil film.

Although the pilot had medical issues and used several medications, none of these should have caused a cognitive issue. Whether or not he had age-related cognitive issues that might have contributed to his failure to recognize the airplane's poor performance and abort the takeoff could not be determined. The instructor had a series of medical conditions, including coronary artery disease, bypass surgery, kidney failure requiring dialysis, chronic back pain, atrial fibrillation, and psychiatric disease. The instructor's serious medical conditions placed him at risk for sudden impairment or incapacitation; however, it is unlikely that these conditions contributed to the accident. Additionally, three central nervous system depressant medications were found in toxicology specimens from the instructor. Due to the limited information from the toxicology testing regarding blood levels of the drugs, it could not be determined whether the instructor's use of multiple impairing medications contributed to the accident.

Text from the NTSB. Open the NTSB docket for WPR16FA124 for the full record.