LEAVENWORTH, WA, USA
N465JR
Garlick TH-1L
The pilot/operator, who had been utilizing the rotorcraft for heavy log lifting operations for the previous 18 months, was initiating a log lift cycle from a hover when the vertical stabilizer separated from the restricted category Garlick TH-1L. The rotorcraft subsequently descended out of control, impacting wooded, sloped terrain. Post-crash metallurgical examination discovered fatigue fractures emanating from a rivet hole within all five layers of the left side aluminum spar cap buildup for the vertical stabilizer. Additionally, fatigue cracking was observed within the tail boom skin near the vertical stabilizer and additional rivets were noted in both sides of the tail boom skin area. The tail boom skin crack was noted to have two separate stop holes drilled in its progression. Maintenance records showed no evidence of an inspection of the spar cap area or internal inspection of the tail cone or vertical fin at the time of installation of six blind rivets in the vertical fin, 18 months previous to the accident. No record was found recording the time of stop-drilling the skin crack progression. Examination of the riveted structure in the vicinity of the tailboom-to-vertical stabilizer junction revealed 30 blind rivets without paint on their exterior or interior ends on the left side of the vertical stabilizer, including seven that were directly adjacent to the separation point in the left cap of the stabilizer front spar. Four similar rivets were noted on the right side of the vertical stabilizer. Helicopter logging operations require repetitive high-stress/high-cycle operations.
HISTORY OF FLIGHT On November 5, 1996, approximately 1400 Pacific standard time, a Garlick TH-1L rotorcraft, N465JR, being operated by Canusa Airlift, Inc. and flown by the company president, a commercial pilot, was destroyed during a collision with terrain following a loss of control when the vertical stabilizer separated while the rotorcraft was engaged in a hover. The accident occurred 29 nautical miles northwest of the Wenatchee airport, Wenatchee, Washington, and the pilot was fatally injured. There was no fire and no flight plan had been filed. Meteorological conditions at the site were unknown at the time of the accident. The flight, which was engaged in logging, was to have been operated under 14CFR133, and originated from a staging site approximately one-eighth of a mile distant. Witnesses reported that the helicopter was in a hover preparing to lift a load of logs when the tail rotor assembly, including the vertical stabilizer, separated from the airframe. The helicopter was observed rotating about its vertical axis as it descended into wooded terrain. PERSONNEL INFORMATION The pilot-in-command, who was also the designated chief pilot, reported to the FAA that he had in excess of 10,000 hours and 16 years of flight experience and commercial helicopter experience respectively. He did not possess an FAA airframe and powerplant mechanic certificate. AIRCRAFT INFORMATION The TH-1L rotorcraft, serial number 157828, was originally manufactured by Bell Helicopter for the US Navy. The aircraft was subsequently surplused by the US military and converted to restricted category civil use under the type certificate maintained by Garlick Helicopters, Inc., Hamilton, Montana. The rotorcraft was registered to Williams Helicopter Corporation on December 7, 1994, and was subsequently sub-leased to Canusa Airlift, Inc. Rotorcraft daily log sheets showed the chief pilot of Canusa flying N456JR at least as far back as April 25, 1995, when the airframe total time was 7640.2 hours. The aircraft total time, based upon aircraft logbooks ending September 24, 1996 (refer to ATTACHMENT I), combined with a running total of flight time by days from September 25, 1996, through November 5, 1996 (refer to ATTACHMENT II), maintained by the operator at the staging area near the accident site, yielded approximately 8198 hours. Documentation revealed that an annual inspection had been conducted on January 19, 1996, at 7,887.3 hours, and had been signed off by an inspector whose FAA inspection authorization (IA) certificate number was 2106741 (refer to ATTACHMENT III). The daily log sheet for the rotorcraft on the same date contained a reference to "annual inspection c/w (see w.o. no. 1966)." This entry, however, was unsigned (refer to upper arrow on ATTACHMENT IV). The bottom of the daily log sheet contained a signoff by an inspector whose FAA airframe and powerplant (A&P) certificate number was 401662013 (refer to lower arrow on ATTACHMENT IV). The most recent rotorcraft daily log sheet record contained an entry dated September 12, 1996, showing the removal, replacement and inspection of the 42 degree gearbox in compliance with Airworthiness Directive 95-10-08 (refer to ATTACHMENT AD-I) at a rotorcraft time of 8,039.8 hours. The entry concluded with "A/C inspected and found airworthy & returned to service." This entry, however, was unsigned (refer to upper arrow on ATTACHMENT V). The inspection signoff block at the bottom right corner of the form was notated "daily #2356390," however, no signature nor airframe/powerplant certificate number were noted (refer to lower arrow on ATTACHMENT V). The number 2356390 was the pilot-in-command's pilot certificate number. The remaining daily log sheet pages covering entries following September 12, (including entries for September 19, 20, 21, 22, 23, and the last page on September 24) contained no references to the 42 degree gearbox (refer to ATTACHMENTS VI, VII, VIII, IX, X, and XI). Additionally, the most recent rotorcraft daily log sheet record contained a page dated May 5, 1996, containing an entry reading "replaced 6 rivits (sic) vert. fin" (refer to ATTACHMENTXII). WRECKAGE AND IMPACT INFORMATION On-site examination of the wreckage was conducted by personnel from the Federal Aviation Administration's Spokane Flight Standards District Office (refer to ATTACHMENT FAA-I). The rotorcraft impacted wooded, moderately down-sloping, snow-covered terrain 29 nautical miles northwest of the Pangborn Memorial airport, Wenatchee, Washington (refer to arrow on CHART I). The latitude and longitude of the accident site were 47 degrees 49 minutes north and 120 degrees 34 minutes west respectively. The rotorcraft came to rest adjacent to several conifer trees. Evidence of rotor blade impacts on the trunks of several trees were observed at the site. The fuselage and tail boom assembly were separated but located approximately 10 feet apart (refer to photograph 1). The vertical stabilizer, including the tail rotor assembly, was located approximately 20 feet upslope from the fuselage (refer to photograph 2). Closer examination of the aft empennage and vertical stabilizer section revealed a separation within the multi-layered, aluminum, spar flange area (refer to arrow in photograph 3). Photographs 4 and 5 show the reconstructed vertical stabilizer and tail boom components (left and right side views respectively) at the separation area. MEDICAL AND PATHOLOGICAL INFORMATION Post mortem examination of the pilot-in-command was conducted by Gerald A. Rappe, M.D., Chelan County Coroner, 227 Grover Court, Wenatchee, Washington, 98801, at the facilities of the Central Washington Hospital morgue, on November 6, 1996. Toxicological evaluation of samples from the pilot-in-command was conducted by the FAA's Toxicology and Accident Research Laboratory. All test results were negative (refer to attached report). TESTS AND RESEARCH The aft tail boom section and vertical stabilizer were shipped to the Safety Board's Materials Laboratory in Washington, DC, for metallurgical examination. Visual examination of the fractures in the tail boom and vertical stabilizer revealed that all breaks were typical of overstress separations except for fracture areas within the left side spar cap of the vertical stabilizer front spar, and a fatigue fracture area in the left side tail boom skin. The tail boom skin fatigue crack initiated from a rivet hole in the top surface of the boom, where the tail boom skin was fastened to the vertical fin skin. The crack progressed largely circumferentially, about 1.3 inches in the inboard direction from the hole and about 2.8 inches in the outboard (then down) direction. The tail boom skin contained two small diameter holes where the crack appeared to have been stop-drilled. These holes were located 2 inches from the rivet hole, on the left side tail boom skin, just below the top of the boom. The fatigue fracture area progressed through one of these holes, and a secondary crack progressed into the other. Examination of the riveted structure in the vicinity of the tail boom to vertical stabilizer joint revealed the presence of blind rivets without paint on their exterior or interior ends. There were 30 of these rivets noted on the left side of the vertical stabilizer including 7 that were directly adjacent to the separation in the left cap of the stabilizer front spar (refer to photograph 5 which shows 6 of these blind rivets). There were 4 such blind rivets noted on the right side of the vertical stabilizer. The left cap fracture was cut from the tail boom piece in order to more easily examine the fracture surface. Magnified examination of the spar cap, composed of a buildup of a single 90 degree aluminum web sheet within which were nested four additional aluminum angles, and the associated rivet hole, revealed the presence of crack arrest positions and smooth, flat (90 degree) fracture regions typical of fatigue cracking on portions of all the sheet pieces. The fatigue cracking initiated from both sides of the rivet hole (refer to attached Metallurgist's Factual Report). ADDITIONAL INFORMATION The rotorcraft logs and records, which were provided to the Safety Board's Investigator in Charge, were returned via Federal Express to the Owner, Williams Helicopter, Inc., 220A Lakeview Road, Ozark, Alabama, 36360, on September 10, 1997. The aft tail boom section and vertical stabilizer were returned to the owner at the same address.
Fatigue failure of the vertical stabilizer spar cap and subsequent loss of the rotorcraft's vertical stabilizer. Factors include inadequate inspection or trouble-shooting of the aircraft tail cone and vertical stabilizer at and after the time sheet-metal skins were stop-drilled and rivets were replaced, and repetitive cycles associated with helicopter logging operations.
Source: NTSB Aviation Accident Database
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