LAX91LA302 · Air Tractor AT-401
Frontier Ag Service Air Tractor AT-401 · Accident: in flight collision with object during initial climb
Event
- NTSB case
- LAX91LA302
- 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
- 0 · 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 AT-401
- Aircraft type
- Air Tractor AT-401
- 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
- N4538K
- Operator
- Frontier Ag Service
- Onboard fatalities
- Unknown
- Route
- From not recordedTo 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
- Initial climb
- 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
- In flight collision with object
- 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
- Other person › Other airport/runway maintenance, performed
- Pilot in command › Visual/aural detection
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
THE INVESTIGATION REVEALED THAT DURING THE DAY ON JULY 9TH, WORKERS FROM THE IMPERIAL COUNTY IRRIGATION DISTRICT ERECTED A LARGE CAUTION SIGN ON THE DEPARTURE RUNWAY ABOUT ONE THIRD OF THE WAY FROM THE START. THAT NIGHT THE PILOT ARRIVED AT THE AIRPORT FOR HIS NIGHT SPRAY RUN AND HE WAS UNAWARE OF THE NEWLY PLACED SIGN. AFTER LOADING THE CHEMICALS TO BE SPRAYED ON BOARD THE AIRCRAFT, THE PILOT TOOK OFF AND THE AIRCRAFT STRUCK THE SIGN WITH THE LEFT SPRAY BOOM. THE BOOM WAS TORN LOOSE FROM THE STRUCTURE, HOWEVER, DID NOT SEPARATE TOTALLY AND BEGAN TO FLAP IN THE AIRSTREAM AS CHEMICALS POURED FROM THE HOPPER. THE PILOT TURNED THE AIRCRAFT TO RETURN TO THE AIRSTRIP AS HE REACHED FOR THE EMERGENCY SHUTOFF VALVE TO STOP THE FLOW OF CHEMICALS. AS THE AIRCRAFT NEARED THE AIRSTRIP, IT COLLIDED WITH A STACK OF HAY BALES RECENTLY ERECTED NEAR THE RUNWAY.
Probable cause
THE ERECTION OF A CONSTRUCTION SIGN ON AN ACTIVE RUNWAY BY COUNTY WORKERS WITHOUT NOTIFYING THE AIRPORT OPERATORS, AND, THE INABILITY OF THE PILOT TO DETECT THE PRESENCE OF THE SIGN DURING THE DARK NIGHT TAKEOFF.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record LAX91LA302
- Event ID
- 20001212X17593
- Case number
- LAX91LA302
- 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: local date, investigation status. Values present in the bulk record are kept.
- The date is the local date; the NTSB stores the UTC date 1991-07-10.
- API snapshot SHA-256: 1c130c6af42180868f5f2187711cdfd1842ff2ae03550e771c10fae92aaf6fc8; retrieved 2026-09-21T23:31:29.545Z.