YAKIMA, WA, USA
N38115
TEXAS HELICOPTER OH-13E
IMMEDIATELY AFTER LIFTING OFF AND REACHING TRANSLATIONAL LIFT, THE PILOT LOST COLLECTIVE PITCH CONTROL AND ROTOR RPM BEGAN TO DECREASE. THE HELICOPTER BEGAN AN UNCONTROLLED DESCENT AND IMPACTED WITH A POND. EXAMINATION REVEALED THAT AN ATTACHMENT BOLT IN THE SCISSOR ARM ASSEMBLY OF THE PITCH CONTROL SUPPORT ASSEMBLY HAD FAILED. EXAMINATION OF THE FRACTURE SURFACE REVEALED THAT THE BOLT HAD FAILED IN FATIGUE, WITH MULTIPLE CRACKING ORIGINS EMANATING FROM THE THREADS OF THE BOLT.
On September 20, 1995, about 1230 Pacific daylight time, N38115, a Texas Helicopter OH-13E, operated by Heli Flight Ag Service, Inc., collided with water and was substantially damaged during an uncontrolled descent into a pond near Yakima, Washington. The uncontrolled descent was precipitated by a flight control malfunction while maneuvering. The commercial pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed and no flight plan had been filed. The aerial application flight departed from Yakima and was conducted under 14 CFR 137. According to an FAA aviation safety inspector from Renton, Washington, the pilot reported that one of the flight controls malfunctioned as the pilot was maneuvering. The helicopter struck a pond and sank. The pilot swam to safety. The helicopter sustained substantial damaged and was recovered. In a written statement prepared by the pilot on October 16, 1995, the pilot stated: ... during a routine spray operation I experienced a broken bolt (AN 175-33) in the scissor arm assembly on the pitch control support assembly. I had just departed from the top of a platform truck over a pond used for [irrigation] located between two orchards. Upon reaching translational lift the collective handle went full pitch. The helicopter starting hopping violently. I tried to get collective pitch down with no luck. Any collective movement only increased the hopping. With throttle wide open I started to [lose] engine and rotor RPM due to full pitch in one blade. Midway across the pond I started to descend because of low RPM. I [flared] back to stop forward airspeed and [attempted] to maintain flight. The tail rotor hit the water first with main rotors chopping tailboom assembly off. An examination of the wreckage by the FAA inspector verified the broken bolt on the scissor arm assembly. The bolt had failed on its threaded portion inside the castellated nut. The fracture surface was cleaned and examined under magnification. The examination revealed fracture features similar to fatigue cracking signatures with multiple ratchet marks emanating from the threads of the bolt. Maintenance records indicated that the helicopter had accumulated 4,196 flight hours prior to the accident, and the helicopter underwent an inspection on May 8, 1995, about 328 flight hours prior to the accident.
FATIGUE FAILURE OF THE BOLT ATTACHING THE SCISSOR ARM ASSEMBLY TO THE PITCH CONTROL SUPPORT ASSEMBLY. THE FAILURE OF THE BOLT LED TO A LOSS OF COLLECTIVE PITCH CONTROL AND REDUCED ROTOR RPM.
Source: NTSB Aviation Accident Database
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