FTW04FA235 · Piper PA-32R-300

A single-engine airplane, operating in dark night instrument meteorological conditions as a Part 135 mail cargo flight, impacted terrain after an in-flight break up. Several minutes before the impact, the pilot reported to air traffic control that he had lost his vacuum pump. An on-site examination of the wreckage revealed that the vacuum pump the drive was separated from the engine and the flex coupling displayed a torsion-type separation with coupling wear consistent with engine operation after the separation. Disassembly of the model 211CC vacuum pump revealed the following. A number was assigned to each of the rotor segments and the corresponding vanes were marked and removed from their respective slots. Five of the six vanes were intact, and vane #4 was broken. Four pieces were reassembled to recreate approximately 80 percent of vane #4. Three of the four pieces were found in the mounting flange, and one piece was found in the back flange. The rotor segments were marked such that vane slot #4 is between segment 4 and segment 5. Upon examination of the walls of vane slot 4, a groove approximately .450 inches by .120 inches by .020 inches deep was found on both sides of the vane slot. These grooves corresponded in dimension and position to the portion of the vane that was missing. Three carbon pieces were found, which exhibited extensive wear, which, in two cases, were smooth and round like a "BB." The rear fracture surface of vane #4 exhibited a smooth, polished, spherical wear mark corresponding with the carbon pieces found. The pump housing had severe wear such that there were washboard marks around its entire circumference. At the bottom of the bore, a burr was found on the edge of one of the back flange discharge ports. Corresponding rotational marks were found on the pump's rotor. According to Parker Hannifin, the rule of thumb for vane wear versus service life is: .025-inches of wear for every 100 hours of operation. Using Parker's original new vane length of .845 inches, the estimated time of operation of the vanes of the accident pump was approximately 1,380 hours. According to Parker the vacuum pump had been overhauled. Parker's service letters require replacement of model 211CC vacuum pumps after 500 hours of operation or 6 years from the date of manufacture, which ever occurs first. Examination of the directional gyro revealed that the housing was intact and the gyro was free to move. No rotational marks were found on the gyro or inside the housing. The turn coordinator gyro was examined and no rotational scoring was found when removed from the housing. A small portion of the housing was fractured and missing. The attitude indicator gyro was free to move within its housing and the housing was intact. No rotational scoring was noted when the gyro was removed from the housing. The filament of the vacuum enunciator bulb # PL33[0] exhibited stretching.

Verbatim NTSB analysis and probable cause from the NTSB dataset