# NTSB LAX99FA057: Bell UH-1H, N4590, Quincy, CA, December 23, 1998 - Type: NTSB accident investigation - Classification: Accident · Fatal · Field investigation · Final report - Date: December 23, 1998, 11:51 local (19:51 UTC) - Place: Quincy, CA - Coordinates: 39.960762, -121.000068 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=39.9608&lon=-121.0001&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Highest injury: Fatal - Injuries: 1 fatal - Status: Completed, report June 21, 2000 - Report: Approved by Office Director - NTSB case key (mKey): 45520 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX99FA057 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/45520/pdf - Page: https://openairdocs.org/ntsb/LAX99FA057 ## Probable cause An inaccurate exhaust gas temperature gauge, that allowed the engine to be run over-temperature unknowingly by the pilot, which resulted in the subsequent failure of the turbine sections. Also causal was the pilot's failure to maintain rotor RPM during the autorotation. A factor in the accident was the operator's failure to adequately perform engine health indicator tests. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(total) - mech failure/malf, hover - out of ground effect - engine instruments,egt/tot gage - output low (cause) - turboshaft engine,free(power) turbine - overtemperature (cause) - turboshaft engine,free(power) turbine - disintegrated (cause) - turboshaft engine,gas generator turbine - overtemperature (cause) - turboshaft engine,gas generator turbine - disintegrated (cause) - rotorcraft operations - performed, pilot in command - maintenance,recordkeeping - inadequate, company/operator management (contributing factor) - Loss of control - in flight, emergency descent/landing - rotor rpm - not maintained, pilot in command (cause) - In flight collision with terrain/water, descent - uncontrolled - terrain condition - water ## Analysis While conducting external load operations, the pilot radioed that the engine had failed. Witnesses reported visually observing the main rotor slowing and the individual blades becoming visible before the helicopter descended steeply into a reservoir from about 200 feet agl. The main rotor driveshaft, main rotor blades, and the tail rotor blades exhibited signatures consistent with low rotor rpm at impact. Engine examination revealed that the gas producer and power turbine assembly had failed as a result of the cumulative effects of thermal stress due to over-temperature operation. Further examination revealed that the exhaust gas temperature harness on the engine had a low signal output resulting in a low EGT indication in the cockpit which caused the company pilots to unknowingly operate the engine in excess of maximum EGT. According to other company pilots who flew this helicopter on typical external load operations, the engine would reach its EGT limit before the maximum torque was achieved. The operator did not routinely perform health indicator tests (HIT checks) which were developed by the U.S. Army to detect changes in engine power output. Review of the helicopter's FAA Type Certificate Data Sheet (H15NM) revealed the requirement for HIT checks to be accomplished prior to each takeoff and recorded in a log record. ## Factual narrative HISTORY OF FLIGHT On December 23, 1998, at 1151 hours Pacific standard time, a Bell UH-1H, N4590, entered an uncontrolled descent following a loss of engine power and impacted in Belden Reservoir, 7 miles west of Quincy, California. The helicopter was destroyed and the commercial licensed pilot was fatally injured. Visual meteorological conditions prevailed for the external load operation that was conducted by Westwind Helicopters, Inc., under 14 CFR Part 133. According to the operator, the helicopter was engaged in a long line external load operation in support of Pacific Gas and Electric Company (PG&E). The pilot was lifting construction equipment, typically in 500 pound loads, from a hillside construction site to a base location at a small resort at the north end of Belden Reservoir. There were three ground witnesses, who were PG&E employees, handling the loading of equipment into the external load sling at the mountain top construction site. The witnesses reported that after 4 or 5 loads had been picked up routinely, the helicopter made an abnormal sound as it approached for the next load. The sound was described by the first witness as "an alarm going off" and "like a beeping." The second said, "It wasn't a beeping but more like a tone," and the third said it was "like a buzzer or like an alarm like a whistle almost." The three said that the pilot then radioed something about it being cold, intake icing and the engine needing more heat. He interrupted the pickup operation and flew around in the area for 2 or 3 minutes before resuming the pickup operation. They then did 5 to 10 more pickups that were routine. After the next pickup, with an external load estimated at only 50 to 75 pounds, one of the witnesses reported that "the helicopter didn't sound quite right . . . I would describe it as a metallic sound like a grinding kind of sound." One of the witnesses noted that as the helicopter flew away with the load the pilot headed toward his landing (refueling) site rather than toward the drop-off zone. The pilot then radioed that he had experienced an engine failure. The witnesses reported that as the helicopter passed from their view behind a ridge, the rotor blades were more visible because they were slowing and the helicopter was in a steep descent. A ground refueler employed by the operator for about 7 years also witnessed the accident. At the time of the accident he was standing on the dam at the south end of Belden Reservoir about 1/3 mile south of the accident site. They were using the dam as a landing site for refueling. He was looking at the ice on the water and subconsciously listening to the helicopter flying in the distance. He "heard the sound change and knew something was wrong." He looked up and the helicopter "came down like a rocket." When asked by the Safety Board investigator if the sound change was in the "whop - whop" of the rotor or the high frequency whine of the engine, he could only say, "all the sound changed." According to the operator, the pilot flew external load operations from the left seat. The engine/main rotor tachometer, torque, EGT, and gas producer rpm gages are located on the right side of the center instrument panel. A 100-foot-long kevlar line was used. AIRCRAFT INFORMATION The aircraft was delivered to the United States Army as an UH-1H in 1965. Following military retirement, it was issued a type certificate in the restricted category in August 1996 following civilian conversation by Western International Aviation, Inc. The operator of the helicopter said that the aircraft is maintained on a 100-hour program and had come out of maintenance on the morning of the accident. The helicopter was in for scheduled replacement of time expired swashplate, scissor sleeve assembly, and rotating control bolts. While the replacement of the time expired items was in progress, mechanics noted that on the right rear engine mount one attachment bolt was broken, the other was loose, and the shims under the mount were laying loose on the engine deck. The mechanics were concerned that some of the shims might have been lost and were reluctant to reassemble the mount without checking the installation alignment of the engine. Although the aircraft was not a Garlik type certificated UH-1H, the mechanics proceeded to realign the engine installation by reshimming in accordance with a Garlik Service Bulletin which, according to the operator, mirrors Bell Helicopter's procedure. The operator reported that several of their pilots had taken checkrides in the helicopter for their U.S. Forest Service authorization card, and that the aircraft had demonstrated satisfactory autorotative landings during those checkrides. The operator also stated that health indicator test (HIT) records were kept in a book in the helicopter. The book was not located among the recovered wreckage. Another pilot reported having flown the accident helicopter under contract to the U.S. Forest Service about 600 hours through the summer of 1998. His last flight in it was on December 20, 1998, 3 days before the accident, when he ferried it to the operator's base at Lincoln, California. He said that through the 600 hours he never had any problem with the helicopter. The aircraft was reliable, and the only unscheduled maintenance he recalled was a blown transmission seal. He also said that "HIT checks" were performed in the field both by him and the accident pilot, who was his supervisor. They were performed about once every 20 flight hours. He thinks they were required by the Forest Service and were recorded on a form provided by the Forest Service. The recordings were taken by the mechanic and were kept at the home base; they were not kept in the aircraft. He was certain that there was no recording of engine parameters on the daily flight log kept in the aircraft. He also recalled that the engine ran up against the temperature limit before it reached the torque limit. It was engine exhaust gas temperature that limited power available, not the torque limit. Review of the helicopter's Federal Aviation Administration (FAA) Type Certificate Data Sheet (H15NM) revealed the requirement for HIT checks to be accomplished prior to each takeoff and recorded in a log record. METEOROLOGICAL INFORMATION A refueler who was present at the time of the accident said that the weather was clear and sunny, cold, and there was little wind. A PG&E foreman estimated the temperature to have been in the mid-30 degree Fahrenheit range. WRECKAGE AND IMPACT INFORMATION The aircraft impacted in the Belden Reservoir near the northwestern shore, approximately 500 feet north of the dam forming the reservoir. The site is at longitude 121 degrees 09.62 minutes west and latitude 40 degrees 04.70 north (GPS). The elevation is approximately 3,000 feet msl. The reservoir, a hydro-electric generating facility on the north fork of the Feather River, is located in a mountain canyon oriented northeast to southwest, and is about 500 feet wide (southeast to northwest) and 1/2 mile long with the dam at the southwest end. On the southeast and northwest side of the reservoir, mountain terrain rises steeply to approximately 2,500 feet above the reservoir level. The shores of the reservoir and the adjacent mountain slopes are densely populated with trees typically 75 feet tall. At the northeast end of the lake is a small resort with a clearing where the helicopter was lowering its external loads; however, the helicopter was landing on the dam itself when necessary to refuel. According to witnesses, at the time of the accident there was approximately 3 inches of snow on the ground, temperatures were in the mid-30 degree Fahrenheit range, and the surface of the lake was covered with a thin layer of ice, mostly in areas near the shore. There was no fire. The aircraft was removed from the reservoir by direction of the Plumas ## Aircraft - Registration: [N4590](https://openairdocs.org/deregistered/N4590-2000-01-07), registration cancelled 2000-01-07, S/N 65-09986 (OpenAirDocs) - Reported make and model: Bell UH-1H - Registry model: [Bell UH-1H](https://openairdocs.org/model/bell-uh-1h) (registry code 1181407) (OpenAirDocs) - Category: Helicopter - Serial number: 65-09986 - Airframe hours: 6774 - Engines: Lycoming T53-L-13B 1400 horsepower turbo shaft - Damage: Destroyed - Flight: Other work use, Part 133 - Registered owner: Westwind Helicopters, Inc. - Airworthiness certificate: Special, Restricted (Special) - Last inspection: 100 hour, October 20, 1998, 36 hours before ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 52; commercial; medical: class 2, valid medical--w/ waivers/lim; seat: left; toxicology performed; flight hours: 15,000 total, 8,000 in this make and model, 100 in the last 90 days, 3 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 160° at 5 knots - Visibility: 3 statute miles - Lowest ceiling: none - Altimeter: 30.00 inHg - Observed at: CIC, 32 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19981223041899A](https://openairdocs.org/incident/19981223041899A), Dec 23, 1998: Bell UH1H, Quincy, CA, Destroyed, 1 fatal. (.19)On December 23, 1998, at 1151 hours pacific standard time, a Bell UH-1H, N4590, entered an uncontrolled descent, impacted an embankment and rolled into… From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.