Piper PA 28-236 N2190H accident near Salmon, Idaho

Probable cause

Maintenance personnel’s improper surface preparation of the accessory mount pad for the installation of the engine’s dry vacuum pump, which resulted in the loss of engine oil, oil pressure, and engine power during flight. Contributing to the accident was the lack of a postmaintenance leak check.

NTSB analysis

Before departing on the personal cross-country flight, the private pilot noted that there was no engine vacuum indication. He took the airplane to a maintenance facility, and a mechanic replaced the vacuum pump. Following the replacement, no leak check was performed; however, vacuum was restored when the engine was started, and the pilot subsequently departed on the flight.

The pilot reported that, about 150 miles from his destination, the engine lost oil pressure. He then turned the airplane toward the nearest airport, and the engine lost power. The airplane was unable to glide to the airport, so he landed it in a hayfield next to the airport. The airplane sustained substantial damage to both wings and the fuselage.

During examination of the engine, holes were found in the top of the case. The engine was covered with oily residue, and oil streaking was found along the bottom of the fuselage. The internal engine parts were fragmented, and the oil filter material was infused with metal fragments.

During examination of the recently installed "dry" vacuum pump, the appropriate fiber gasket was found in place between the pump body and the accessory mounting pad surface. The gasket appeared intact, and neither side (mating surface) showed signs of tearing or surface scuffing, peeling, or separation. The internal (dry) area was partially filled with oil, and all of the internal parts had oily residue. Oil staining was found on both sides of the gasket and around the accessory pad's pressure crankcase oil passage hole (used for "wet" pump installations), and extended along the internal cavity edge and the exterior perimeter of the pump base on three of its four sides. The pressure crankshaft oil galley hole was not sealed as recommended in the engine manufacturer's service instructions for the installation of a dry vacuum pump.

Further, the engine accessory mounting pad was examined, and it had remnants of gasket material not associated with the installed gasket adhered to it, making the surface rough and uneven. It is likely that the new dry pump was installed on an improperly cleaned surface and that this condition, in conjunction with the unsealed galley hole, allowed the engine oil to vent to the exterior of the engine and resulted in the loss of engine oil and oil pressure, internal engine damage, and the subsequent loss of engine power. If a postmaintenance leak check been performed, the oil leaking through the seal or hole would have been detected.

Text from the NTSB. Open the NTSB docket for WPR14LA345 for the full record.