On September 16, 1999, an Air Tractor AT-502B (registration N5092G) was involved in an aviation accident near Anguilla, MS. Investigators recorded the probable cause as: The P3 air line disconnected at the P3 air filter housing , and a 'B' nut not being safetied by maintenance personnel, which resulted in a total loss of engine power. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During an agricultural application flight at low altitude, the turbine engine lost all power. The pilot executed a forced landing in a cotton field, causing the aircraft to nose over. Examination found a disconnected P3 air line and an unsafetied B nut.
Incident
During an agricultural application flight, the pilot was conducting a swath run at an altitude of 10 to 15 feet when the turbine engine experienced a total loss of power. The pilot performed a forced landing in a cotton field, during which the airplane nosed over.
Investigation
Post-incident examination revealed that the P3 air line at the P3 filter housing was disconnected. Additionally, the 'B' nut securing the line was not safety wired. The engine maintenance manual includes a note stating, 'Make sure the P3 line to the filter and FCU is disconnected before performing a motoring compressor wash to avoid contamination...'
Maintenance Background
The airframe and power plant mechanic who conducted the last recorded 200-hour maintenance inspection reported that he did not remove the P3 air line during the inspection. He stated that the 'B' nut had slipped through without being safetied.