NTSB Identification: FTW91LA061.
The docket is stored on NTSB microfiche number 44662.
Accident occurred Saturday, April 06, 1991 in SAN YGNACIO, TX
Probable Cause Approval Date: 03/24/1993
Aircraft: CESSNA 150D, registration: N4437U
Injuries: 2 Serious.

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 PIC ASKED THE PASSENGER RIDING IN THE LEFT SEAT IF HE WANTED TO SEE HOW THE AG PILOTS FLEW. HE REDUCED POWER TO IDLE AND DOVE DOWN TOWARD AN OPEN FIELD. AFTER TRAVERSING THE FIELD THE PILOT ADDED POWER AND THE PASSENGER HEARD A 'POP OR BANG' NOISE FROM THE ENGINE AND THE PILOT SAID 'OH MY GOD'. THE AIRPLANE SUBSEQUENTLY IMPACTED IN THE FIELD IN A SHALLOW NOSE DOWN ATTITUDE AND A SLIGHT LEFT BANK AND CART-WHEELED. INVESTIGATION REVEALED THAT CONDITIONS WERE PRESENT FOR CARBURETOR ICING AND THAT THE CARBURETOR ACCELERATOR PUMP WAS NOT ACTUATING SMOOTHLY. THE CARBURETOR HEAT CONTROL WAS FOUND JAMMED TO THE FULL ON POSITION FOLLOWING THE ACCIDENT; HOWEVER, IT COULD NOT BE DETERMINED IF THAT WAS THE CONDITION PRIOR TO IMPACT.

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

POWER LOSS DUE TO CARBURETOR ICE AND A MALFUNCTIONING CARBURETOR HEAT CONTROL AND THE PILOT'S LOSS OF CONTROL OF THE AIRPLANE.

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