# NTSB DFW07LA138: Air Tractor AT-401, N92PK, Oak Grove, LA, June 6, 2007 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: June 6, 2007, 11:00 local (16:00 UTC) - Place: Oak Grove, LA - Coordinates: 32.861667, -91.389442 - Nearby events: https://openairdocs.org/map.md?lat=32.8617&lon=-91.3894&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report November 29, 2007 - Report: Approved by Office Director - Parties: FAA/FSDO - NTSB case key (mKey): 66000 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DFW07LA138 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/66000/pdf - Page: https://openairdocs.org/ntsb/DFW07LA138 ## Probable cause A complete loss of power due to failure of the impeller drive gear train and displacement of the blower spring drive mechanism, which resulted in seizure of the propeller shaft/crankshaft. Also causal was the failure of the phenolic separator bracket of the rear impeller support bearing for undetermined reasons. A factor was the none suitable terrain for the forced landing. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power, maneuvering - aerial application - compressor assembly,impeller - failure (cause) - compressor assembly,oil seal - failure (cause) - compressor assembly,air seal - failure (cause) - Forced landing, descent - emergency - In flight collision with terrain/water, emergency descent/landing - terrain condition - rough/uneven - terrain condition - none suitable (contributing factor) ## Analysis The 5,475-hour commercial pilot reported that after performing an aerial application pass in his radial-engine-powered airplane, he initiated a turn to reverse direction to start another pass. At the top of the turn, he heard a loud bang from the radial engine, followed by the sound of the engine winding down. He also noticed white smoke from the exhaust, a loss of power, and a drop in manifold pressure. The pilot made an forced landing to a field, where the airplane rolled about 250 yards before it flipped over. The airplane was released to the owner after the accident, who later sold it to another operator. Due to the damage sustained in the accident, the engine was disassembled and examined before the new owner could return the airplane back to service. The new owner provided an engine disassembly report. According to the report, "undetermined causes resulted in distress to the phenolic separator bracket of the rear impeller support bearing resulted in its separation and fragmentation." The reports adds that "this initiated a chain reaction of events throughout the rest of the engine as clearances, lack of lubrication and subsequent wearing of engine components took place." This damage ultimately resulted in destruction of the blower labyrinth seal and the impeller gear train, which reduced power output. The engine reports concludes that "the destroyed impeller drive gear train and the distress caused by the displaced blower spring drive mechanism, coupled with reduced power output, resulted in seizure of the propeller shaft/crankshaft and complete loss of power." ## Factual narrative On June 6, 2007, approximately 1100 central daylight time, a single-engine Air Tractor AT-401 agricultural airplane, N92PK, was substantially damaged during a forced landing following a loss of engine power while maneuvering near Oak Grove, Louisiana. The commercial pilot, sole occupant of the airplane, was not injured. The airplane was registered and operated by the Whittington Air and Ground LLC of Eudora, Arkansas. Visual meteorological conditions prevailed and no flight plan was filed for the aerial application flight conducted under 14 Code of Federal Regulations Part 137. The local flight originated from a private airstrip near Eudora, Arkansas, at 1015. The 5,475-hour commercial pilot reported that after performing an aerial application pass, he initiated a turn to reverse direction to start another pass. At the top of the turn, the pilot "heard a loud bang, followed by a sound like something at high RPM was winding down, also noticed white smoke from the exhaust." The pilot subsequently reported a "noticeable loss of power," and noticed that the manifold pressure had "fallen to 16 or 17 inches." Following the loss of engine power, the pilot executed a forced landing to a field. During the landing roll on the field, the tailwheel-equipped airplane rolled for "about 250 yards before turning upside down." The airplane came to rest in the inverted position and the pilot was able to egress the airplane unassisted. According to the Federal Aviation Administration (FAA) inspector, who responded to the accident site, the horizontal stabilizer sustained structural damage. The airplane was released to the owner after the accident, who later sold the airplane to another operator. Due to the damage sustained in the accident, the engine was disassembled and examined before the new owner could return the airplane back to service. The new owner provided a report of their findings from the engine disassembly. According to the Covington Aircraft, Radial Division Engine Investigation Report, "Undetermined causes resulted in distress to the phenolic separator bracket of the rear impeller support bearing resulted in its separation and fragmentation." This resulted in a chain reaction of events throughout the rest of the engine as clearances, lack of lubrication and subsequent wearing of engine components took place. This damage ultimately resulted in damage of the blower labyrinth seal and the impeller gear train, which reduced power output. According to the report, "the destroyed impeller drive gear train and the distress caused by the displaced blower spring drive mechanism, coupled with reduced power output, resulted in seizure of the propeller shaft/crankshaft and complete loss of power." A review of engine's maintenance history revealed the 600 horsepower R-1340 radial engine had accumulated a total of 5,016.3 hours. The engine underwent a major overhaul 580.3 hours prior to the accident. The last major overhaul was performed as result of a propeller strike. At 1053, the weather observation facility at the Monroe Regional Airport (MLU), near Monroe, Louisiana, located approximately 37 miles west-southwest of the accident site, reported wind variable from 150 degrees to 220 degrees at 10 knots, visibility 10 statute miles, clear skies, temperature 88 degrees Fahrenheit, dew point 68 degrees Fahrenheit, and a barometric pressure setting of 29.91 inches of Mercury. ## Aircraft - Registration: [N92PK](https://openairdocs.org/deregistered/N92PK-2009-03-24), registration cancelled 2009-03-24, S/N 401-0821, built 1991 (OpenAirDocs) - Reported make and model: Air Tractor AT-401 - Registry model: [Air Tractor AT-401](https://openairdocs.org/model/air-tractor-at-401) (registry code 0390204) (OpenAirDocs) - Registry engine: [Pratt & Whitney R1340 series](https://openairdocs.org/engine/pratt-whitney-r1340-series) (registry code 52016, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 401-0821 - Airframe hours: 4680 - Engines: Pratt & Whitney R-1340 ANI 600 horsepower reciprocating - Damage: Substantial damage - Flight: Aerial application, Part 137 - Operator: Whittington Air & Ground LLC, doing business as Whittington Air & Ground LLC - Registered owner: Whittington Air & Ground LLC - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Annual, May 1, 2007, 40 hours before - Departed: Eudora, AR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 34; injuries: none; commercial; airplane ratings: single-engine land; medical: class 2, without waivers/limitations; last flight review February 1, 2006; seat: single; flight hours: 5,475 total, 70 in this make and model, 5,082 as pilot in command, 200 in the last 90 days, 110 in the last 30 days, 8 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 180° at 10 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 88 °F, dew point 68 °F - Altimeter: 29.90 inHg - Observed at: KMLU ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 20070606012229A](https://openairdocs.org/incident/20070606012229A), Jun 6, 2007: Airtrc AT401, Oak Grove, LA, Substantial damage. (-23) Engine lost power during turn-around maneuver at end of spraying pass and aircraft made an emergency landing in open field and became inverted after… From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.