NTSB Factual Report

On August 13, 2014, about 1215 mountain daylight time, a Piper PA-28-236 airplane, N2190H was substantially damaged during landing, following a loss of engine power and emergency descent from cruise flight, near the Lemhi County Airport (KSMN), Salmon, Idaho. The airplane was registered to and operated by the private pilot as a visual flight rules (VFR) personal cross-country flight under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and the pilot was not injured. The sole passenger received minor injuries. The airplane departed Gooding Municipal Airport (KGNG), Gooding, Idaho, about 1054 for Kalispell City Airport (S27), Kalispell, Montana, and no flight plan had been filed.During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on August 13, the pilot said that during run-up, prior to departing Gooding, he noted that there was no engine vacuum indication. He took the airplane to a maintenance facility at the Gooding Airport, and the vacuum pump was replaced. He said that following the replacement of the vacuum pump, a leak check was not performed. The mechanic replaced the cowls, and told the pilot to give him a "thumbs up" if he had vacuum when the engine was started. After starting the engine and observing that he had engine vacuum, he gave the signal and departed for Kalispell in the airplane. About 150 miles north of Gooding, the pilot heard an unusual noise from the engine, and noted a loss of engine oil pressure. He turned toward the nearest airport, which was Lemhi County, and made a mayday call on 121.5 Mhz. The pilot believed he had enough altitude and airspeed to make it to the airport. Approaching the airport, it was clear that he would be short of the airport, and he elected to land in a hayfield next to the airport. After touchdown in the field, the airplane encountered a road perpendicular to his direction of travel, which collapsed the landing gear, and the airplane slid through the airport's perimeter fence.

The airplane sustained substantial damage to its wings and fuselage. No preaccident mechanical anomalies, with the exception of the vacuum pump replacement and subsequent loss of engine oil pressure and power, were reported.

The airplane was recovered to a maintenance facility at the Lemhi County Airport, where an airframe and engine examination were conducted by the National Transportation Safety Board (NTSB) investigator-in-charge assisted by a local mechanic.

Engine Examination

The engine was not removed from the airplane or disassembled. An exterior examination of the engine showed several holes in the top of the case near the centerline joint. The holes were narrower at the bottom than at the top, consistent with force being applied from the interior of the case. The engine was covered with oil residue, and oil pooled in low areas of the case exterior and around the engine accessories. Additionally oil streaking was noted along the underside of the fuselage.

Peering through the holes in the case, fragmentation of the internal engine parts was seen. The oil filter was cut apart and the internal filter material was laid out and examined. The filter material was infused with metal fragments.

The recently installed "dry" vacuum pump, which does not rely on pressurized oil from the crankcase for internal lubrication, was located on the upper aft right side of the engine. The upper aft right side area of the engine was covered in oil residue, with oil pooled in low areas. The vacuum pump mounting base is square with mounting holes in each corner, and was mounted on an engine accessory pad and secured with four mounting studs secured to the case with four nuts. A fiber gasket is used between the dry vacuum pump and the accessory pad.

The vacuum pump was removed. The four studs and nuts were in place; however an accurate break-torque could not be ascertained. A fiber gasket was in place between the pump body and the accessory pad surface.

An examination of the pump showed that the internal (dry) area was partially filled with oil, and all the internal parts had oil residue and oil pooling.

An examination of the fiber gasket showed that it was the proper gasket for the dry pump installation. There was oil staining on both sides of the gasket. Gasket oil staining was evident around the accessory pad's pressure crankcase oil passage hole, and extended along the internal cavity edge and outward to the exterior perimeter of the pump base on three of its four sides. The gasket appeared intact and neither side (mating surface) showed signs of tearing or surface scuffing, peeling, or separation.

The engine accessory mounting pad was examined, and appeared to have remnants of gasket material, not associated with the previously examined gasket, adhered to it, making the surface rough and uneven. The "dry" pump cavity was partially filled with oil, and all the internal areas had oil residue. The pressure crankshaft oil galley hole, used with a "wet" pump installation, was not plugged.

Additional Information

The accident airplane's engine was designed to operate a "wet" vacuum pump, which uses pressurized oil from the engine crankcase to lubricate the pump's internal moving parts. Consequently, the accessory pad had an oil passage hole to provide pressurized crankcase oil to the pump.

With the installation of the "dry" vacuum pump, which does not require pressurized crankcase oil for internal lubrication, the oil passage hole serves no purpose. With the proper installation and security of the appropriate gasket, the oil passage hole is covered/sealed. The proper gasket was used in the accident airplane's installation.

Acknowledging the possibility of a faulty pump installation or subsequent loosening of the pump, the engine manufacturer published Textron Service Instruction No. 1369 dated October 6, 1978 which states in part; "to avoid an oil leak in the event a vacuum pump should become loose, it is recommended that the oil passage be sealed off as described in the following paragraphs …," which describes the optional installation of a threaded plug to preclude the loss of engine oil.

NTSB 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.