On March 27, 1997, about 1711 Alaska standard time, a wheel equipped Piper Navajo PA-31-350 airplane, N4105D, operated by Grant Aviation, received substantial damage when an in-flight fire erupted in the left engine nacelle while on approach to landing at the Nome Airport, Nome, Alaska. The airline transport certificated pilot and the two nonrevenue company employees aboard were not injured. The airplane is owned and operated by Grant Aviation, Emmonak, Alaska, and was returning without cargo or revenue-producing passengers from an earlier 14 CFR Part 135 cargo flight. At the time of the accident, the airplane was being operated as a 14 CFR Part 91 positioning flight.

According to the company's Director of Operations, the airplane was on a 1/4 to 1/2 mile final approach in the traffic pattern at Nome Airport, when the pilot noticed a large amount of flame coming from the left engine nacelle. The pilot immediately shut off the fuel supply to the left engine and made an uneventful landing. After landing, the pilot noticed that the fire was still burning, although to a lesser degree. He used the on-board, hand held Halon fire extinguisher on the fire. Moments later, the local fire department arrived and extinguished the residual fire.

Postaccident inspection of the engine by a Federal Aviation Administration inspector and company maintenance personnel, disclosed a leaking fuel line on the left engine. The leaking fuel line connected the engine driven fuel pump and the fuel injector servo. The fuel line was removed and forwarded to the NTSB investigator-in-charge for examination and testing. Testing disclosed that the fuel line was extensively damaged by fire. The line had been installed in an area that was heavily burned and sooted during the fire, and which was in close proximity to the engine driven fuel pump.

The accident airplane's left engine, a Lycoming IO-540-J2BD, was shipped to the Textron Lycoming manufacturing plant in Williamsport, Pennsylvania, pending inspection.

On June 6, the engine was examined under the direction of an NTSB air safety investigator from the North Central Region. The engine examination disclosed that the area which exhibited the most fire damage was behind the engine driven fuel pump. The fuel pump was attached to the test stand's fuel supply and pressurized. The fuel pump began leaking at 8 pounds pressure per square inch (psi). The leak was coming from the area where the relief valve cover mated with the fuel pump body. The fuel pump was removed, and the safety retaining wires securing the screws on top of the relief valve cover were inspected. The safety wiring was intact. The safety wires were removed, and the screws were found to be only finger tight. The screws were replaced and torqued to the recommended torque value of 25 inch pounds. The pump was pressurized to 20 psi (the maximum available at the test stand), and no leaks were observed.

The fuel pump, Lear Romec part number RG9080J7A, serial number D-648, was removed from the engine and transported by the North Central Region NTSB investigator to a site where a pressure equivalent to the maximum working pressure of the fuel pump could be approximated. The pump's retaining screws were torqued to 25 inch pounds, and 50 psi was applied to the pump. The pump did not leak. The retaining screws were loosened until they were finger tight, pressure was reapplied, and the pump leaked.

An internal examination of the fuel pump disclosed that the two required gaskets on the relief valve cover were present and appeared to be serviceable.

Subsequent testing of seven similar, new pumps, by Lycoming at their manufacturing plant, revealed four of the seven pumps leaked in the area where the relief valve cover joins the pump body. The leaks occurred at less than the fuel system's maximum working pressure. The valve cover retaining screws were found to be tightened below the recommended torque settings.

Lycoming issued Service Bulletin (SB) 406, dated November 19, 1976, which addressed leaks affecting Lear Romec fuel pumps. The SB indicated the cover attaching screws could be the source of fuel leaks due to the gasket material taking a set. The SB directed that the pumps be inspected for leaks, and that all screws used to assemble the pump be checked for proper torque values.

Lear Romec issued SB 101SB018, dated July 16, 1987, which also referenced fuel leakage past the relief valve cover gasket on certain pumps, and called for a one time inspection and tightening of the relief valve cover screws.

During this investigation, Lear Romec issued Service Bulletin 101SB020, dated July 8, 1997 which addresses initial inspection, checking the torque of the fuel pump relief valve cover screws, and time limits for repetitive inspections. Lycoming also issued Service Bulletin 406A, which mimics the Lear Romec SB.

The accident airplane's engine was overhauled by Lycoming on September 23, 1996. At that time, a new fuel pump was installed, and Lycoming certified that all applicable airworthiness directives and service bulletins had been complied with for the engine and its accessories. The overhauled engine was installed on March 15, 1997. At the time of the accident, the engine had been in service 29.8 hours.

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