# NTSB LAX91LA302: Air Tractor AT-401, N4538K, Calexico, CA, July 10, 1991

- Type: NTSB accident investigation
- Classification: Accident · Minor injuries · Limited investigation · Final report
- Date: July 9, 1991, 23:30 local (Jul 10, 1991, 06:30 UTC)
- Place: Calexico, CA
- Coordinates: 32.690521, -115.51062 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=32.6905&lon=-115.5106&mi=10
- Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping)
- Highest injury: Minor injuries
- Injuries: 1 minor
- Status: Completed, report March 31, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 27282
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX91LA302
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/27282/pdf
- Page: https://openairdocs.org/ntsb/LAX91LA302

## 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.

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- In flight collision with object, takeoff - initial climb
  - object - sign
  - other airport/runway maintenance - performed, other person (cause)
  - information unavailable, pilot in command
  - light condition - dark night
  - visual lookout - not possible, pilot in command
  - visual/aural detection, pilot in command (cause)

## Analysis

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.

## Aircraft

- Registration: [N4538K](https://openairdocs.org/deregistered/N4538K-1994-10-05), registration cancelled 1994-10-05, S/N 4010770 (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)
- Category: Airplane
- Serial number: 401-0770
- Engines: P&W R-1340 600 horsepower reciprocating
- Damage: Destroyed
- Flight: Aerial application, Part 137
- Operator: Frontier Ag Service
- Registered owner: Frontier Ag Service
- Last inspection: Unknown, January 2, 2000

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 55; commercial; airplane ratings: single-engine land, multi-engine land; medical: class 2, valid medical--w/ waivers/lim; flight hours: 8,100 total, 1,400 in this make and model, 160 in the last 90 days, 3 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Night/dark
- Wind: 250° at 6 knots
- Visibility: 30 statute miles
- Lowest ceiling: none
- Temperature: 81 °F

## 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 19910709026639A](https://openairdocs.org/incident/19910709026639A), Jul 9, 1991: Airtrc AT401, Imperial, CA, Destroyed. Unknown to pilot barrier sign on runway prior night takeoff. Hit sign went around and struck hay bales on landing.

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.