RAINIER, WA, USA
N6166R
Bell UH-1H
While preparing to sling a load of logs, the pilot noticed several changes in engine noise level followed by two loud bangs and a total loss of power. He executed an autorotation/landing into a small clearing directly beneath the rotorcraft as no other suitable site was available. During the forced landing, the helicopter was damaged. Disassembly of the ex-military, Allied Signal (Lycoming) T53-L-13BA turboshaft engine revealed that the number 21 forward bearing (P/N 1-300-082-01B) had disintegrated. The engine had a total of 4202.4 operating hours of which 199.4 were accrued since entering the civilian operating environment. Nonmandatory Service Bulletin No. 0056 provided procedures for replacing this bearing with an improved bearing (P/N 1-300-082-03), within 400 hours after receipt of the bulletin.
HISTORY OF FLIGHT On April 4, 1996, approximately 0820 Pacific standard time, a Garlick HH-1K (formerly a military Bell UH-1H) restricted category rotorcraft, N6166R, registered to and operated by Northwest Helicopters, Inc., and being flown by a commercial pilot, was substantially damaged upon impact with terrain during an auto-rotative emergency landing following a total loss of power. The rotorcraft crashed approximately 11 miles southeast of Rainier, Washington. The pilot was uninjured and variable meteorological conditions existed at the time. The rotorcraft, which was engaged in logging, was to have been operated under 14CFR133, and originated from a point near the accident site approximately 35 minutes prior to the accident. The pilot reported that the rotorcraft had been engaged in log lifting operations when he "noticed a minute change in noise level." After adjusting the power he determined that "everything seemed normal" and then lowered the log sling line in preparation for another log lift. He reported that "at that time the noise level changed again" and he then began to maneuver to return to the service landing site. He was then radioed by the ground crewman of smoke coming from the rotorcraft's exhaust and noted that the master caution light had illuminated. The pilot reported hearing two loud bangs and observed the EGT, N1, N2, and NR all begin to unwind. Immediately thereafter, he "looked for a landing area and found only a hole in the timber right below" and then executed an auto-rotation into that site. AIRCRAFT INFORMATION The rotorcraft was equipped with an Allied Signal (Lycoming) model T53-L-13BA turboshaft engine, serial number LE15957. Although this was a military model number designation and the equivalent commercial model number designation is T53-13B, the data plate affixed to the engine was that for a commercial engine rather than a military data plate. The "A" suffix on the model number is a military designation pertaining to the fuel control configuration. The information on the data plate was observed to have been applied with a vibro-peen type tool. It could not be determined at what point in the engine's history the military data plate was removed and replaced with the civilian data plate. The engine was manufactured in 1967 and was obtained from the military by the operator in early 1993 with 4003.0 hours total time since new. The engine was first installed in N6166R on January 8, 1996, with the same total time. According to maintenance records, the engine had accumulated 4202.4 hours total time since new, and 1252.4 hours time since last overhaul at the time of the accident. The total time on the number 21 forward bearing could not be determined. The bearing had not been changed subsequent to the engine's leaving military service and the total civil engine time was 199.4 hours. ADDITIONAL INFORMATION The engine was partially disassembled at the facilities of Allied Signal Aerospace, Phoenix, Arizona, on July 2, 1996. The disassembly results were reported in Allied Signal report number 21-9263, and revealed that the number 21 forward bearing, P/N USA FP96 1-300-082-01B, had disintegrated. The roller bearings were observed to be heavily deformed and the forward (geared) end of the accessory drive shaft had separated from the remainder of the shaft thus depriving the fuel pump of rotational input. The oil within the engine was observed to be generally clear but with particulates suspended within. Avco Lycoming Service Bulletin No. 0056, which was issued August 28, 1986, and applies to T53-L-13 series engines that are non-U.S. military, was issued to "introduce forward power shaft bearing 1-300-082-03 having improved reliability." The service bulletin provided instructions for replacing the forward power shaft bearing and was to be accomplished on "engines within 400 operating-hours after receipt of (the) bulletin." Verbal release of the engine was provided to Mr. Steven Macon of Allied Signal on August 11, 1996, and written wreckage release was accomplished on September 20, 1996 (refer to attached NTSB Form 6120.15).
failure of the forward power shaft (number 21) bearing. A factor relating to the accident was: the lack of suitable, unobstructed terrain for an emergency landing.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
