Winamac, IN, USA
N428JT
Terpstra Exec 162F
The experimental amateur-built rotorcraft impacted terrain during cruise flight following the in-flight separation of the vertical stabilizer, which resulted in damage to the tail rotor. The rotorcraft was registered to and built by the pilot. The pilot did not hold a rotorcraft rating and received a 90-day solo endorsement to pilot the rotorcraft approximately 10 months before the accident. Examination of the vertical stabilizer revealed fatigue fracture of the vertical stabilizer bracket originating from hole burrs. The airplane construction manual states, "It is good practice to remove all sharp edges when working with sheet metal. Various types of deburring tools are available, or use a file or sandpaper."
On August 18, 2007, at 1530 eastern daylight time, an experimental amateur-built Terpstra Exec 162F rotorcraft, N428JT, built and owned by the pilot, received substantial damage on impact with terrain following the reported in-flight separation of the helicopter's vertical stabilizer. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 personal flight was not operating on a flight plan. The pilot held a private pilot certificate without a rotorcraft rating. The pilot was fatally injured. The flight originated from Arens Field Airport (RWN), Winamac, Indiana at an unknown time. A witness saw the vertical stabilizer separate from the rotorcraft. The vertical stabilizer was located approximately 1,200 feet south of the main wreckage, which was located approximately 5 miles south of RWN. The pilot held a private pilot certificate with a single-engine land airplane rating. The pilot's logbook contained three 90-day solo flight endorsements in the Exec 162F on April 24 2006, September 17, 2006, and October 10, 2006, by the same certified flight instructor (CFI). Only the 90-day solo endorsements dated April, 24, 2006 and October 10, 2006 were preceded by entries of flight instruction. Examination of the tail rotor revealed that it had separated but was collocated with the main wreckage. The vertical stabilizer was sent to the National Transportation Safety Board's Materials Laboratory for examination. The examination of the vertical stabilizer revealed a 0.1 inch thick formed steel bracket was fractured at an angle just above the upper bolt hole connecting the bracket to the stabilizer. The fracture intersected two other unfilled holes in the bracket, resulting in a fracture with three separate ligaments. Portions of the center ligament immediately above the attaching bolt displayed light surface corrosion. The other fracture areas were clean. Close optical examination of the separation area revealed fracture features and deformation patterns consistent with fatigue cracking at multiple locations in all three ligaments. Fatigue propagation was visible emanating from the edges of the holes in each of the three ligaments. The fatigue initiated at four single origins located at the sharp corner intersections of the holes with the outboard surface of the bracket. The hole edges had no visible radius or chamfer and a machining burr was present at the initiation of the forward fracture. The intersections of the holes with the inboard bracket surface were similarly sharp 90 degree corners as were all the other hole corners on the bracket. Fatigue propagation from the outboard surfaces penetrated inward and longitudinally through most of the bracket cross sections. Additional fatigue regions initiated at multiple locations on the inboard surface of the bracket and progressed directly outboard through the bracket. The airplane construction manual states, "It is good practice to remove all sharp edges when working with sheet metal. Various types of deburring tools are available, or use a file or sandpaper." The Federal Aviation Administration’s Final forensic Toxicology Fatal Accident Report of the pilot states: 0.007 (ug/ml, ug/g) diphendyramine detected in blood and present in urine. Diphenhydramine (commonly known by the trade name Benadryl) is an over-the-counter antihistamine with sedative effects, often used to treat allergy symptoms or as a nighttime sedative. An autopsy of the pilot was conducted by the Pulaski County Coroner on August 19, 2007. The autopsy report cited the cause of death as multiple blunt force trauma.
The inadequate installation of the horizontal stabilizer bracket by the pilot, the fatigue fracture seperation of vertical stabilizer bracket during cruise flight, and the aircraft control not possible by the pilot.
Source: NTSB Aviation Accident Database
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