LAX00FA169 · Air Tractor 502A
San Tan Dusters Air Tractor 502A · Accident: airframe, component or system failure while maneuvering
From HIGLEY, AZ to an unrecorded destination
Event
- NTSB case
- LAX00FA169
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 1 · all aircraft and ground
- Ground fatalities
- 0
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- General aviation
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Air Tractor 502A
- Aircraft type
- Air Tractor 502
- Category
- Airplane
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N15466
- Operator
- San Tan Dusters
- Onboard fatalities
- Unknown
- Route
- From HIGLEY, AZTo not recorded
- Aircraft age
- Not recorded
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 137: Agricultural
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- Maneuvering · aerial application
- First occurrenceThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Airframe, component or system failure
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Destroyed
Cause areas
- Manufacturer › Procedures/directives, inadequate
- Wing, spar › Failure, total
- Wing, spar › Fatigue
Approximate · Estimated position: the centre of Queen Creek, AZ, the place the record names. Not the accident site.
NTSB narrative
The airplane was spraying chemicals on a field of crops when the left wing separated in flight. Ground witnesses said that the airplane was making a level spray pass over a potato crop when the left wing failed. No unusual meteorological phenomena were observed in the area, and the airplane did not perform any unusual maneuvers prior to the failure. The left wing's lower spar cap was found to have fractured in fatigue at a point that transected the inboard attach block bolt hole where the spar attaches to the center section spar carry through member. Multiple origin sites were identified within the bolt hole bore, with corrosion pitting evident at the origin points. The spar caps met the hardness, chemistry, and microstructure of the production drawing specified material. Air Tractor Service Letter 118 and the maintenance manual specify an inspection procedure, which calls for the removal of the hopper for a detailed inspection of the spar caps for cracks; one area identified as critical for cracking was the inboard bolt hole bore. The inspection interval was specified as every 2,000 hours or 3 years. The number of crack arrest striations in the fatigue region was determined from the first point the crack would be visible from beneath the attach block during the specified inspection, and the mean time for the fatigue crack to progress from detectible during the inspection to failure was calculated to be about 105 hours. Examination of the right wing lower spar cap revealed the presence of multiple fatigue cracks emanating from corrosion pits within the outboard bolt hole bore. No maintenance records were located for either the airframe or engine. A mechanic was located who performed some periodic maintenance on the aircraft. He stated that during the removal of the hopper in May 1997, 2 years 11 months prior to the accident, he had accomplished the 2,000-hour check of the wing spars in the area of the attach bolts as required by Service Letter 118. Based on other records, the aircraft was believed to have flown an average of 500 hours per year and would have accumulated only 1,500 hours since the inspection.
Probable cause
The fatigue failure and in-flight separation of the left wing due to the manufacturer's underestimation during the aircraft design process of the time interval from fatigue crack initiation to failure, and, the manufacturer's subsequent specification of an inadequate inspection interval.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record LAX00FA169
- Event ID
- 20001212X20838
- Case number
- LAX00FA169
- Dataset
- historical-pre2008
- Source SHA-256
- 89e2df6d848e7ab3b42e7d7c7a03ff403303057a26ca04c95b3ea67201c3ce74
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: 7a0a05ca5a258929eb4c373e43c96845312c4eb7875a4c2e32093d7375ebcdd8; retrieved 2026-09-20T21:17:45.637Z.