Cause of Sikorsky S-61A Air Crash in Lakehead, CALIFORNIA, USA on 3/26/2002





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Final Report on Probabable Cause of Crash

HISTORY OF FLIGHT

On March 26, 2002, at 1538 Pacific Standard Time, a Sikorsky S-61A twin-engine helicopter, N318Y, was destroyed when it impacted trees and terrain following a loss of control while maneuvering near Lakehead, California. The helicopter was registered to and operated by Croman Corporation of White City, Oregon. The commercial pilot was fatally injured and the commercial co-pilot sustained serious injuries. Visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations Part 133 external load flight. The local flight originated from a staging area near the McCloud River, at 1500.

According to the operator, the helicopter maneuvered for approximately 40 minutes in the area as part of a logging operation prior to the accident. One witness, who was a ground worker, was in radio contact with the pilot. The worker stated that the pilot was supposed to drop chokers near him. A choker is a steel cable that is fitted around a log, and is standard equipment for logging operations. The chokers were attached to a hook that hung from a 200-foot long-line connected to the helicopter. The witness stated that he had radioed to the pilot and informed the pilot that he had moved 100 yards toward Mount Shasta, thus providing the pilot with a reference point to drop the chokers, and the pilot acknowledged. There were no further radio transmissions received from the pilot. The helicopter did not drop the chokers at the point the witness expected, and it over flew the intended drop zone. The witness stated that the helicopter appeared to be gliding, and he observed a tan smoke coming from the engine/transmission area. He stated, "the blades were not moving as fast as they should have been," and "the blades were coning extensively." He added that "the blades were hardly rotating and they were pointing toward the clouds." Two other witnesses reported the main rotor blades had slowed down and they could count each blade. Subsequently, the helicopter "fell like a rock," impacted the ground, and a fire eventually erupted.

The one witness, who described the blade coning, indicated it took him approximately 5 minutes to get to the accident site. While he was making his way to the accident site, the helicopter caught fire (within less than a minute). As the witness approached the helicopter he heard "the engines…running, surging up and down, up and down." Another witness indicated he heard no engine noise when the helicopter over-flew his position.

PERSONNEL INFORMATION

The pilot-in-command (PIC) held a commercial pilot certificate with the following commercial ratings: rotorcraft-helicopter, airplane single- and multi-engine land, and instrument airplane and helicopter. He held a flight instructor certificate with a rotorcraft-helicopter rating; however, it was not current. He was type rated in the Sikorsky SK-58 and SK-61 helicopters (SK is the FAA designator for Sikorsky type ratings). On September 15, 1993, the PIC completed the requirements to act as pilot-in-command for external load operations that are set forth in FAR Part 133 (class A, B, and C). On the morning of the accident the pilot successfully completed a proficiency check in the accident helicopter, in accordance with FAR 61.58. According to a form provided by Croman Corporation, the PIC had accumulated a total of 25,800 flight hours, of which 20,000 hours were in external load operations, and 15,000 hours were in the S-61. He held a second-class medical certificate that was dated January 25, 2002, with the stipulation that he possess glasses that correct for near vision.

The co-pilot was issued a commercial helicopter certificate on November 29, 2000. He also held a flight instructor certificate for helicopters that was issued on March 28, 2001. According to a form provided by Corman Corporation, the co-pilot had accumulated a total of 295.35 flight hours, of which 288.95 hours were in external load operations in the S-61A. He held a second-class medical certificate that was dated April 4, 2001, with the stipulation that he wear corrective lenses.

AIRCRAFT INFORMATION

The helicopter (serial number 61094) was manufactured in 1962, and was an all-metal, semi-monocoque construction, and was equipped with a 5-blade main rotor system and a 5-blade tail rotor system. The helicopter utilized fixed landing gear without sponsons in place of the original sponson-mounted retractable landing gear. The helicopter was involved in an accident in 1972, which resulted in two fatalities. The FAA listed the helicopter as destroyed as a result of that accident, but it was rebuilt in 1975 by Carson Helicopters, and registered in the restricted category in July 1980, by Croman Corporation. The helicopter was configured for logging operations. The helicopter was listed on Croman's Supplemental Type Certificate, which authorized the use of S-61L/N (20600 series), or S-61R (23000 series) main transmissions. At the time of the accident, the helicopter was utilizing a 23000 series main transmission.

The helicopter was also equipped with two 1500-horsepower General Electric (GE) CT58-140-1 turboshaft engines. The GE CT58-140-1 engine is an axial-flow turboshaft engine incorporating the free turbine principle. Output power is extracted by a free turbine, which is mechanically independent of the gas generator rotor system. The gas generator consists of a ten-stage compressor, annular combustor and two-stage turbine. "Efficient and stall-free operation" is ensured by use of the variable stator principle in the compressor. The inlet guide vanes and stator vanes (in stages 1, 2, and 3) are variable. The turbine section includes a gas turbine section (Ng), which consists of two turbine rotors that provide rotational power to the compressor, and a power turbine (free turbine; Nf), which consists of one turbine rotor that extracts energy from the exit gases and coverts it to shaft horsepower for useful work. Engine performance is monitored by various engine instruments, including the torquemeter indicator (two needles labeled 1 and 2 for the #1 and #2 engine, respectively), and the triple tachometer (three needles labeled 1, 2, and R for #1 power turbine speed, #2 power turbine speed, and main rotor RPM, respectively).

Croman Corporation maintained the helicopter, and on October 24, 2001, the main gearbox was removed from the helicopter and replaced with a serviceable main gearbox. The main gearbox then underwent an overhaul inspection in accordance with the Sikorsky overhaul manual (SA4045-83). On December 18, 2001, the helicopter was removed from service and a major inspection was started in accordance with the Sikorsky Major Inspection Guide (SA 4047-14). During the inspection the overhauled main gearbox was re-installed. On February 26, 2002, at a helicopter total time of 41,761.7 hours, the #1 and #2 engines were replaced with the same engines that were involved in the accident. The #1 engine (left hand engine; serial number 296-018D) was installed at an engine total time of 17,239.7 hours, with a total time since overhaul of 435.4 hours. The #2 engine (right hand engine; serial number 295-057) was installed at an engine total time of 26,764.7 hours, with a total time since overhaul of 5,632.2 hours. The major inspection was completed on March 6, 2002, 76.1 hours prior to the accident. On March 21, 2002, the helicopter underwent a phase C inspection (zones 9 hull, 6 fuel cell installation, 2 power plant; #2 engine). The inspection was accomplished 11.5 hours prior to the accident.

According to maintenance personnel, on the morning of the accident the helicopter flew 5.9 hours. At noon the following helicopter systems/components underwent a visual condition check: the main rotor system, main gearbox, flight controls, #1 engine, and #2 engine. According to the maintenance entry for March 26, 2002, the following Airworthiness Directives (AD) and Service Bulletins (SB) were complied with: AD 79-12-10 (tail rotor blade ultrasonic check), AD 68-20-08 (automatic flight control system functional check), AD 78-

Initial Report

The twin-engine helicopter impacted trees and terrain following a likely loss of power in the left engine while maneuvering. According to one witness, as the helicopter overflew his position, he observed the main rotor blades rotating very slowly to the point where they were coning and each blade could be viewed individually. This witness observed a tan smoke emanating from the transmission area. The helicopter then "fell like a rock," and impacted the ground. The witness indicated he heard the engines surging when he reached the accident site. Another witness did not hear any engine noise as the helicopter passed overhead. A post crash fire consumed the cabin, main transmission case, and, heavily damaged both engines. A post-accident examination of the helicopter revealed the main rotor and tail rotor blades sustained little to no leading edge damage though the helicopter fell through 150-foot pine trees. The number 1 engine displayed no rotational damage to its internal components. The number 2 engine sustained heat and tip rub damage to the 1st and 2nd stage gas turbine blades in a manner that suggested the damage occurred while the rotors were rotating. Numerous components from each engine were completely destroyed by the post-accident fire and could not be examined. The main rotor transmission case was nearly burned away. The exposed transmission gears displayed no signs of pre-existing anomalies; however, complete continuity of the transmission could not be established due to thermal damage. The number 1 and number 2 input free wheeling units were examined and displayed no signs of improper operation. The cockpit sustained severe fire damage; however, the left side triple tachometer and both left and right side torque indicators were examined. The torque indicators both displayed the number 1 engine torque at 13 percent, while the number 2 engine torque indication was only available on the left torque indicator, which displayed a number 2 engine torque reading of 140 percent.
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2002 Sikorsky CALIFORNIA

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