What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
Tail rotor gear box seperated during spray run. Spiralled to ground. (.4)the pilot initiated a right turn, then he felt and heard a thump. He lowered the collective and attempted to straighten from the turn. He felt a strong vibration and the nose of the aircraft pitched down. A ground crewman who witnessed the accident reported that while the helicopter was about 35 feet AGL, he saw a large piece of the tail and a rotor blade fly off the ship, followed by the tail rotor hub assembly, the remaining blade, and the 90-degree gearbox. The helicopter began a 360-degree right spiral, made 2 1/2 rotations, and then impacted the ground in a 30-degree nose-down attitude. He further noted that the engine still seemed to be producing about 60 percent power. The tail and tail rotor gearbox was found about 125 feet from the fuselage. Metallurgical examination of the vertical tail fin, tail rotor gearbox, and tail rotor blades disclosed an area of chafing which wore through the vertical fin's spar and initiated a fatigue crack. The fatigue crack initiated in an area where the vertical fin driveshaft cover fastened on the left side of the aircraft near the upper end. Chafing had oc curred between the cover and the spar, wearing away the spar. According t Bell, the UH-1B requires a daily inspection to visually check the area of the upper vertical fin, per the aviation unit technical manual, where the fatigue cracking occurred. (-23) while spraying a field and climbing out to clear telephone wires, the tailrotor and transmission separated from the tailboom at approx 75 feet of altitude. The aircraft spun two and one half times and struck the ground flat (belly down).
As the FAA filed it
TAIL ROTOR GEAR BOX SEPERATED DURING SPRAY RUN. SPIRALLED TO GROUND. (.4)THE PILOT INITIATED A RIGHT TURN, THEN HE FELT AND HEARD A THUMP. HE LOWERED THE COLLECTIVE AND ATTEMPTED TO STRAIGHTEN FROM THE TURN. HE FELT A STRONG VIBRATION AND THE NOSE OF THE AIRCRAFT PITCHED DOWN. A GROUND CREWMAN WHO WITNESSED THE ACCIDENT REPORTED THAT WHILE THE HELICOPTER WAS ABOUT 35 FEET AGL, HE SAW A LARGE PIECE OF THE TAIL AND A ROTOR BLADE FLY OFF THE SHIP, FOLLOWED BY THE TAIL ROTOR HUB ASSEMBLY, THE REMAINING BLADE, AND THE 90-DEGREE GEARBOX. THE HELICOPTER BEGAN A 360-DEGREE RIGHT SPIRAL, MADE 2 1/2 ROTATIONS, AND THEN IMPACTED THE GROUND IN A 30-DEGREE NOSE-DOWN ATTITUDE. HE FURTHER NOTED THAT THE ENGINE STILL SEEMED TO BE PRODUCING ABOUT 60 PERCENT POWER. THE TAIL AND TAIL ROTOR GEARBOX WAS FOUND ABOUT 125 FEET FROM THE FUSELAGE. METALLURGICAL EXAMINATION OF THE VERTICAL TAIL FIN, TAIL ROTOR GEARBOX, AND TAIL ROTOR BLADES DISCLOSED AN AREA OF CHAFING WHICH WORE THROUGH THE VERTICAL FIN'S SPAR AND INITIATED A FATIGUE CRACK. THE FATIGUE CRACK INITIATED IN AN AREA WHERE THE VERTICAL FIN DRIVESHAFT COVER FASTENED ON THE LEFT SIDE OF THE AIRCRAFT NEAR THE UPPER END. CHAFING HAD OC CURRED BETWEEN THE COVER AND THE SPAR, WEARING AWAY THE SPAR. ACCORDING T BELL, THE UH-1B REQUIRES A DAILY INSPECTION TO VISUALLY CHECK THE AREA OF THE UPPER VERTICAL FIN, PER THE AVIATION UNIT TECHNICAL MANUAL, WHERE THE FATIGUE CRACKING OCCURRED. (-23) WHILE SPRAYING A FIELD AND CLIMBING OUT TO CLEAR TELEPHONE WIRES, THE TAILROTOR AND TRANSMISSION SEPARATED FROM THE TAILBOOM AT APPROX 75 FEET OF ALTITUDE. THE AIRCRAFT SPUN TWO AND ONE HALF TIMES AND STRUCK THE GROUND FLAT (BELLY DOWN).
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.