# NTSB WPR24LA070: Air Tractor AT-502A, N6126U, Stratford, CA, January 10, 2024 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: January 10, 2024, 10:10 local (18:10 UTC) - Place: Stratford, CA · Blair Air Private field - Coordinates: 36.204833, -119.79411 - Nearby events: https://openairdocs.org/map.md?lat=36.2048&lon=-119.7941&mi=10 - Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping) - Defining event: [Initial climb: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report February 11, 2026 - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: Pratt & Whitney Canada Corp., Federal Aviation Administration, Transportation Safety Board of Canada - NTSB case key (mKey): 193638 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR24LA070 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/193638/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=193638 - Page: https://openairdocs.org/ntsb/WPR24LA070 ## Probable cause A partial loss of engine power due to the malfunction of the engine compressor bleed-off valve. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine bleed air system: compressor bleed valve](https://openairdocs.org/ntsb-findings/01057532): Aircraft › Aircraft power plant · Malfunction (probable cause); cases with it: [Air Tractor AT-502A, 1 case](https://openairdocs.org/ntsb-findings/01057532/cases.md?model=0390306), [All aircraft, 4 cases](https://openairdocs.org/ntsb-findings/01057532/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Initial climb: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Air Tractor AT-502A, 2 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=0390306), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) ## Analysis The pilot was repositioning an empty agricultural airplane for fertilizer application. During takeoff, the airplane failed to develop full power. At about 200 feet above ground level (agl) the engine rolled back to near idle. The pilot’s attempt to vary the power lever inputs did not affect engine power output, and he initiated a forced landing into a grove of small pistachio trees and soft dirt. Postaccident examination of the engine and follow-up bench testing of the engine compressor bleed-off valve (BOV) revealed an abnormal amount of air leaking around the piston. Disassembly of the BOV revealed a piston ring set was stuck within the piston groove, consistent with an abnormal air leak and irregular function. Abrasive and adhesive wear was observed on the piston rings and piston groove. The wear was likely due to environmental contaminants or twisting in the BOV’s metal piston ring profile. Based on the condition of the BOV’s rings, the BOV likely did not fully close during the accident flight, which resulted in a partial loss engine power during takeoff. ## Factual narrative On January 10, 2024, about 1010 Pacific standard time, an Air Tractor AT-502A airplane, N6126U, was substantially damaged when it was involved in an accident near Stratford, California. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 positioning flight. The pilot reported that the airplane was being repositioned to another location to apply fertilizer and that the hopper was empty. During takeoff the airplane failed to develop full power. At about 200 ft agl, the engine rolled back to near idle. The pilot’s attempt to vary power lever inputs did not affect engine power output. Unable to maintain altitude, the pilot maneuvered the airplane between two houses into a grove of small pistachio trees and soft dirt. The gas generator compressor turbine (CT) was still running when the pilot got out of the airplane. He shut off the fuel and secured the engine. The airplane sustained substantial damage to the wings. The fuel tanks in both wings were breached. Fuel was observed in the surrounding areas under the airplane. Power control continuity was established from the cockpit controls to the engine. The high-pressure pump filter and last-chance filter were removed: visual examination revealed that both contained fuel and were clean. A fuel sample was obtained from the fuel farm and no contaminants were found. The engine was shipped to the engine manufacturer for additional examination and testing. No preaccident mechanical malfunctions or failures with the airframe that would have precluded normal operation were observed. Examination of the engine at the engine manufacturer’s facilities revealed the power section, of the engine showed buckling and rotational internal contact of the exhaust casing which was consistent with the accident sequence to the power turbine section. An alternate power section was provided by the manufacturer and was installed on the gas turbine section of the engine to facilitate an engine operational check. The engine was installed in the test cell and started normally. Following a short dwell period at ground idle speed to raise the oil temperature, the engine slowly accelerated to approximately 35,000 rpm (95% Ng). The test cell plenum pressure change confirmed that the compressor bleed-off valve (BOV) closed during engine acceleration. Subsequent review of the data showed the BOV was slow to close. The test cell T5 temperature (inter turbine temperature) readings began to fluctuate, and the engine was shut down for troubleshooting. Engine testing was interrupted due to a slave PS wire harness malfunction and ended to prevent the risk of overtemperature. Review of the engine run test data and hesitation heard during the engine sweep was consistent with a compressor BOV malfunction. Subsequent bench testing of the BOV revealed air leakage around the piston and P3 feed gasket. Bench test pressure check of the BOV revealed an abnormal amount of air leaking around the piston.Disassembly of the BOV revealed a piston ring set was stuck within the piston groove, consistent with an abnormal air leak and irregular function. Abrasive and adhesive wear was observed on the piston rings and piston groove, consistent with the environmental debris and/or by the twist observed on the BOV metal piston ring. During the disassembly of the BOV, two assembly part numbers were vibro-peened by hand on the BOV cover, with neither of the two-part numbers having a strike through. A review of the maintenance records revealed that the BOV had been disassembled, cleaned, inspected and repaired in April of 2012 by Dallas Airmotive, which is a designated overhaul facility for Pratt & Whitney Canada. This BOV was not installed on the engine at delivery. ## Aircraft - Registration: [N6126U](https://openairdocs.org/aircraft/N6126U), registered now, S/N 502A-0298, built 1995 (OpenAirDocs) - Reported make and model: AIR TRACTOR INC AT-502A - Registry model: [Air Tractor AT-502A](https://openairdocs.org/model/air-tractor-at-502a) (registry code 0390306) (OpenAirDocs) - Registry engine: [Pratt & Whitney PT6A series](https://openairdocs.org/engine/pratt-whitney-pt6a-series) (registry code 52032, turbo-prop) (OpenAirDocs) - Category: Airplane - Serial number: 502A-0298 - Year built: 1995 - Airframe hours: 11195 - Engines: Pratt & Whitney PT6A-65R 1173 horsepower turbo prop - Damage: Substantial damage - Flight: Positioning, Part 91 - Operator: Blair Ground Services - Registered owner: R & D Leasing Inc - Airworthiness certificate: Special, Restricted (Special) - Last inspection: 100 hour, November 5, 2023, 26 hours before - Departed: PVT, Lemoore, CA - Destination: D86, Visalia, CA - Airport: Priv, Blair Air, runway 36, 3,900 × 60 ft, gravel - Equipment: Electronic multifunction display, Stall warning system ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 69; injuries: none; commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review March 4, 2023; seat: single; restraint: 3-point; flight hours: 28,147 total, 28,047 as pilot in command, 40 in the last 90 days, 9 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: 330° at 5 knots - Visibility: 10 statute miles - Temperature: 48 °F, dew point 39 °F - Altimeter: 30.19 inHg - Observed at: KNLC, 11 nm away - METAR: KNLC 101756Z 33005KT 10SM FEW090 FEW220 09/04 A3019 RMK AO2 SLP222 RH/71 T00940044 10094 20022 51010 ## 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 20240110000059A](https://openairdocs.org/incident/20240110000059A), Jan 10, 2024: Air Tractor Inc AT-502A, Stratford, CA, Substantial damage. After aircraft takeoff at roughly 200 feet altitude pilot in command reported the aircraft lost engine power. Made an emergency landing in nearby orchard.… ## Docket (13 files) The files NTSB released with the investigation on February 11, 2026, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=193638. 54.2 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 11 pages, 3.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16619871&FileExtension=pdf&FileName=N6126U%20accident%20report%20stamped_Redacted-Rel.pdf - Mor pilot's statement (item 2, PDF, 1 page, 67 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19677516&FileExtension=pdf&FileName=Record%20of%20e-mail%20correspondence%20Ken-Rel.pdf - Mor FAA interview (item 3, PDF, 1 page, 76 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19678368&FileExtension=pdf&FileName=MOR%20FAA%20Phone%20Interview%20Jason-Rel.pdf - Engine exam summary (item 4, PDF, 11 pages, 2.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19678977&FileExtension=pdf&FileName=Exam%20Summary%20Report%20Final_Redacted-Rel.pdf - Bov pwc email summary (item 5, PDF, 1 page, 72 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19680864&FileExtension=pdf&FileName=Record%20of%20e-mail%20correspondence%20PWC-Rel.pdf - Engine monitoring file (item 6, CSV, 258 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19480557&FileExtension=csv&FileName=Engine%20monitoring%20file-Rel.csv - Engine logbook #2 excerpt (item 7, PDF, 16 pages, 9.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19480228&FileExtension=pdf&FileName=N6126U%20engine%20logbook%20%232%20Excerpt_Redacted-Rel.pdf - Engine logbook #3 (item 8, PDF, 26 pages, 19.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19480375&FileExtension=pdf&FileName=N6126U%20engine%20logbook%20%233_Redacted-Rel.pdf - Propeller logbook (item 9, PDF, 9 pages, 9.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19480547&FileExtension=pdf&FileName=N6126U%20propeller%20log_Redacted-Rel.pdf - Airframe logbook #2 part 2 (item 10, PDF, 10 pages, 6.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19480000&FileExtension=pdf&FileName=N6126U%20Airframe%20logbook%20%232%20part%202_Redacted-Rel.pdf - NTSB certification of party representative form (item 11, PDF, 2 pages, 382 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19589202&FileExtension=pdf&FileName=NTSB_Investigation_Party_Form%20WPR24LA070%20signed_Redacted-Rel.pdf - Release of wreckage WPR24FA070 (item 12, PDF, 1 page, 30 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19678859&FileExtension=pdf&FileName=Release%20of%20Wreckage%20WPR24FA070-Rel.pdf - Photo array (item 13, PDF, 6 pages, 2.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19678436&FileExtension=pdf&FileName=Photo%20array%20WPR24LA070%20BOV-Rel.pdf 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.