Introduction
On May 8, 2009, at approximately 1030 central daylight time, a twin-engine Cessna 421B, registration N60HG, was substantially damaged during a forced landing following a loss of engine power shortly after takeoff. The accident occurred near Alpine, Texas. The commercial pilot, who was the sole occupant, received minor injuries. The airplane was registered and operated by O'Hara Flying Service of Amarillo, Texas. Visual meteorological conditions prevailed, and no flight plan was filed for the positioning flight destined for Rick Husband Amarillo International Airport (AMA) in Amarillo, Texas.
Pilot Report
According to the pilot, shortly after takeoff, when the airplane was about 400 feet above the ground, the right engine stopped producing power. As the pilot reached to feather the right engine, the left engine surged and sounded as if it were going to quit. The pilot then advanced the engine controls and began searching for a suitable location for a forced landing. He noted that he did not feel he had full power available from the left engine. The airplane subsequently impacted several small bushes during the off-airfield landing.
Examination Findings
A Federal Aviation Administration (FAA) inspector who responded to the accident site reported that the airplane had an adequate supply of fuel, which appeared consistent with 100LL aviation grade fuel.
An examination of the aircraft wreckage was conducted by the National Transportation Safety Board (NTSB) Investigator-in-Charge, along with technical representatives from the airframe and engine manufacturers, at Air Salvage of Dallas on May 28, 2009. Data from a JPI engine monitor was downloaded, revealing a sudden decrease in cylinder head temperature (CHT) and exhaust gas temperature (EGT) readings for the right engine. A visual inspection of the engine showed that the idler gear support pin, located on the rear of the motor, had backed out. The retaining hardware for the idler pin—two nuts and lock washers—was missing. The movement of the idler pin allowed the idler gear to drop, causing it to become disconnected from the magneto drive gears, resulting in a loss of engine ignition. The idler gear teeth were severely worn, and the accessory drive gears on the cam and crankshafts were either ground down or broken. Disassembly of the engine revealed numerous metal pieces in the oil sump.
Examination of the left engine and its engine monitor readings showed no apparent abnormalities. The left engine was rotated to obtain thumb compression and drive train continuity. Each cylinder was borescoped, and the spark plugs were light gray in color and appeared normal. The magnetos were removed and rotated by hand, producing a spark at each terminal. The engine's oil filter was cut open, inspected, and found to be clear of any metal debris.
Conclusion
The investigation determined that the right engine failed due to a loss of ignition caused by the backing out of the idler gear support pin and the subsequent disconnection of the idler gear from the magneto drive gears. The left engine was found to have no mechanical issues that would have prevented normal operation.