NTSB Identification: LAX91LA302.
The docket is stored on NTSB microfiche number 44877.
Accident occurred Tuesday, July 09, 1991 in CALEXICO, CA
Probable Cause Approval Date: 03/31/1993
Aircraft: AIR TRACTOR AT-401, registration: N4538K
Injuries: 1 Minor.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

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.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

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.

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