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Franklin Crash Investigation Focuses on Fuel Servo

By Fareed Guyot, Manager – Electronic Publications, EAA 388642
Kyle and Amanda Franklin

April 14, 2011 — As Kyle Franklin and his wife Amanda continue to recover from their injuries as a result of a crash last month, NTSB investigators are focusing on a fuel system component that may be susceptible to damage during engine backfires. Kyle was preparing to enter a climbing maneuver and as he advanced the throttle on his Waco biplane he experienced an “abnormal engine operation” according to NTSB Senior Air Safety Investigator Aaron Sauer. A burst of flame came out of the exhaust and there was a partial loss of engine power. Kyle advanced the throttle again in an attempt to get the engine running, which prompted more flames from the exhaust and a total loss of power. 

The engine on the Waco is a Pratt & Whitney R-985 radial and features a Bendix fuel injection servo system. To test the engine the Bendix servo was removed and cylinders five and six, which had impact damage, were replaced. The engine fuel pump ran normally when bench tested.

The fuel servo was bench tested and found to be operating normally at high power settings but a slightly high mixture at moderate and low power, Sauer reported. Internal inspection of the servo found a lever that was bent within the unit. Sauer said that an engineer familiar with the unit stated that during engine backfires, the reverse pressure flow through the servo can bend the lever and affect the fuel/air mixture.

The engine on Franklin’s airplane had undergone a complete overhaul 40 hours prior to the accident. Sauer said that the internal lever was not bent by the crash impact but may have been bent when Franklin experienced the engine anomaly or in the previous 40 hours since overhaul.
“We don’t know the answer to that and I don’t know if we ever will,” Sauer told EAA.

In 1988 Precision Airmotive purchased many of the Bendix fuel servo lines but it is not known if the company supports the servo that was on Franklin’s plane. Sauer said the testing and examination of the aircraft components is complete; however, he is awaiting recommendations from Precision on whether further testing of the servo will provide additional insight.

Sauer said that he has not had a chance to interview Kyle at length about the accident due to his wife’s difficult recovery from severe burns sustained in the crash, but he wished the best for the Franklins.

“Tremendous support from all the folks involved,” Sauer said of the investigation.  “I wish nothing but the best and continued progress for Kyle and Amanda with the injuries they sustained.

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