Aircraft: Cessna T210. Injuries: 4 Fatal. Location: Armonk, N.Y. Aircraft damage: Destroyed.
What reportedly happened: Witnesses observed the 4,150-hour pilot doing multiple engine run-ups both on the parking ramp and at the end of the runway prior to departure. They reported that the engine initially idled rough. Shortly after takeoff from runway 34, the pilot informed the air traffic controller that he needed to return to the airport and requested runway 16.
He declared an emergency but did not state the nature of the emergency. The airplane crashed one mile from the approach end of runway 16 and caught fire. The wreckage path through trees indicated that the airplane came down on a shallow glide angle with the landing gear and flaps retracted.
A disassembly and examination of the engine revealed that the No. 2 cylinder piston head exhibited severe thermal deterioration consistent with a pre-ignition or detonation event. The electrodes of the No. 2 cylinder spark plugs were fully imbedded with aluminum and appeared incapable of producing a spark. The other five cylinders appeared to be functional and were undamaged. The left magneto was set to 30° before top dead center (BTDC). The manufacturer’s specification was 22° BTDC. The right magneto was broken at its mount and its timing could not be verified.
Examination of the engine maintenance records revealed that the magnetos were last retimed during an annual inspection about 27 months before the accident. The airplane was flown infrequently since the engine was installed in 2007.
The airport was equipped with noise abatement monitoring microphones that captured the airplane on the outbound and inbound legs of the accident. Although the engine appeared to be running just prior to impact, the engine sound pressure recorded on the outbound leg was significantly greater than on the inbound leg, suggesting that the pilot was approaching the airport at a reduced power setting. Investigators determined it is likely that additional power was available had the throttle been advanced.
Probable cause: The pilot’s decision to depart on the flight with a suspected mechanical deficiency and his subsequent decision to fly the final approach at a reduced power setting. Contributing to the accident was the improper timing of the magnetos that resulted in a severe detonation event.
NTSB Identification: ERA11FA349
This June 2011 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.