N4788C

On November 30, 1996, at 0934 hours mountain standard time, a Cessna T210N, N4788C, was substantially damaged during a forced landing following a loss of power upon departure from Scottsdale, Arizona. The pilot and four passengers received serious injuries. Visual meteorological conditions prevailed for the personal cross-country flight and an IFR flight plan was filed. The flight was en route to San Diego, California.

Postaccident examination of the engine revealed that the number 2 piston exhibited detonation/preignition damage with upper ring land failure and heavy piston scoring, erosion, and metal transfer to the piston skirt. A burn hole was observed through a piston ring groove into the interior of the piston. The top rings were fragmented. The lower ring was intact, but seized in its groove. The top edge of the piston crown was melted and eroded away over 80 percent of the piston circumference.

The piston was shipped to the engine manufacturer for examination and analysis under the supervision of the FAA MIDO inspector. According to the report, the failure was caused by detonation/preignition due to undetermined causes. The report also listed some possible causes of this type of event.

Both of the engine driven magnetos were shipped to the manufacturer's facility at Atlanta, Georgia. Functional testing and teardown examination was conducted under the supervision of the FAA MIDO inspector. According to the report, all installed parts were appropriate part numbers and in proper condition and adjustment. The magnetos were functional tested to the FAA approved TCM data. Both magnetos meet the test specifications of the data.

The turbo controller was hand carried by a Safety Board investigator to the Allied Signal turbo division at Torrance, California, for functional testing. According to the test results the controller met the manufacturer's FAA approved test data.

The engine fuel system was removed and shipped to the manufacturer, Continental Motors. The examination and functional testing was supervised by the FAA MIDO inspector. Some of the "O" ring seals had dried out from storage without fuel. The examination revealed that they exhibited the ability to flow fuel and appeared to be capable of functioning properly on the engine's fuel system. The items that were functional tested met the manufacturers specifications.

According to a dictionary of aeronautical terms, detonation (a reciprocating engine condition) is an uncontrolled explosion inside the cylinder of a reciprocating engine. Detonation occurs when the pressure and temperature inside the cylinder become higher than the critical pressure and temperature of the fuel. The pressure rise inside the cylinder caused by the fast moving flame front can heat and compress the unburned fuel-air mixture enough for it to explode, or release it's energy almost instantaneously. Detonation releases the energy faster than the engine can accept it, and the engine is likely to be damaged.

Preignition (reciprocating engine malfunction) is ignition of the fuel-air mixture inside the cylinder of an engine before the normal spark occurs. Preignition can be caused by an incandescent piece of carbon or by any other sharp edge or point inside the cylinder that gets red-hot.