NTSB Factual Report

HISTORY OF FLIGHT

On March 23, 2003, at 0800 central standard time, a Sikorsky S-61A, N81664, registered to and operated by Carson Helicopters Incorporated, collided with trees and subsequently the ground and burst into flames during a logging operation in a remote area near Kimble, Tennessee. The flight was conducted under the provisions of Title 14 CFR Part 133 for external load operations and visual flight rules. Visual meteorological conditions prevailed at the time of the accident. The commercial pilot was fatally injured and the commercial rated co-pilot received serious injuries. The helicopter was substantially damaged. The flight departed the staging area near Kimble, Tennessee, at 0730 on March 23, 2003.

According to the co-pilot, the purpose of the flight was to move logs from one-drop area to another using a 150-foot long line attached to the helicopter. On the second airlift, shortly after the logs were laid on the ground, a shudder was felt in the helicopter airframe followed by a slight yaw to the right. On the instrument panel, there was a needle jump in the triple tachometer gauge followed by a very loud bang. The pilot asked, what was that? The co-pilot replied, 'I think we just had a bad input slip". The helicopter began a violent left hand descending spin towards the ground. At this point the pilot stated, "I'm losing it, I'm losing it, pull the throttles". As the helicopter descended, it collided with trees and subsequently the ground. After the helicopter came to a complete stop the co-pilot exited the helicopter. Within seconds an explosion was heard, the helicopter burst into flames. The radio ground guide assisted in the ground handling of the operation. As the helicopter descended the radio ground guide departed the area but returned to the accident site to assist after the helicopter came to a complete stop.

PERSONNEL INFORMATION

The pilot was issued a commercial pilot certificate on August 17, 1994, with airplane single- engine land and rotorcraft-helicopter, (VFR ONLY). Review of the pilot records revealed that he had a total flight time of 29,325 hours, and a total of 5,300 flight hours in the Sikorsky S-61A. The commercial pilot held a second-class medical certificate dated April 2, 2001, valid when wearing corrective lenses for near vision.

The co-pilot was issued a commercial pilot certificate on July 17, 2000, with airplane single and multiengine land airplane, helicopter and instrument airplane. Review of the pilot records revealed a total helicopter flight time of 4,742, flight hours and a total of 2030 flight hours in the Sikorsky S-61A. The commercial pilot held a second-class medical certificate dated March 6, 2002.

AIRCRAFT INFORMATION

The helicopter was originally delivered to the US Navy as a Sikorsky Aircraft HSS-2, Bureau Number 148989, in October 1961. It was later altered by Carson under FAA form 337 and registered as N81664 in the FAA's Restricted Category by Carson as an S-61A. The helicopter was equipped with two General Electric CT-58-140-1 turbo-shaft engines. The left engine, serial number: 280-107 MA had a total time of 21,529 hours, and 411 hours since overhaul. The right engine, serial number: 285-243 had a total time of 7,616 hours, and 4,638 since overhaul. The helicopter's last inspection was a continuous airworthiness inspection, preformed on March 22, 2003, at a total time of 18,580 hours.

METEOROLOGICAL INFORMATION

The Chattanooga Love Field Airport weather observation facility reported at 0753 central standard time, sky condition: few at 10000 feet AGL, visibility 10 statue miles, temperature 9 degrees Celsius, dew point 7 degrees Celsius, and altimeter 30.05.

WRECKAGE AND IMPACT INFORMATION

Examination of the wreckage site revealed the helicopter came to rest 75 feet down a ravine on its left side. There were freshly broken trees approximately 50 feet above the wreckage site. The lower pick up hook of the long-line rested on a dirt path with approximately a 50-foot section of long-line extending down towards the helicopter. The 150 foot long-line assembly displayed fire damage. The cockpit and the main fuselage of the helicopter were fire damaged. The tail boom was partially fire damaged, and tail rotor blades were bent and connected to the tail rotor transmission. The tail rotor drive shaft was intact and connected to the main rotor transmission. The five main rotor blades were connected to the main rotor head and displayed buckling and deformation damage. A 38-foot section of the long-line was found on one of the main rotor blades. The engines were fire and deformation damaged.

Examination of the airframe revealed, the forward and main cabin sections were fire damaged. The tail cone and pylon were charred, and several areas within the wreckage revealed congealed aluminum material. The tail landing gear area was intact and soot residue was also present. The left main landing gear assembly was fire damaged. The right main landing gear assembly was buckled.

All five main rotor blades were recovered at the accident site. No evidence of leading edge damage was noted. The tail rotor was intact with bending, and scoring on the blades. The tail rotor head was still mounted to the vertical pylon section, and the pitch change links were bent. Examination of the main rotor head revealed all five main rotor blade spindles were damaged, and attached to the main rotor head, and the droop flap stops were damaged.

Examination of the transmission and drive shafts established that the tail rotor gearbox had rotational continuity from the tail rotor drive shaft at the intermediate gearbox back to the tail rotor head. Examination of the intermediate gearbox revealed that it was still mounted to the base of the vertical pylon. The intermediate gearbox chip detector was examined, and no chips were noted on the magnetic pick-up. Examination of the tail rotor driveshaft revealed that all five sections were found in their normally installed positions. Continuity was established from the tail takeoff drive at the main gearbox back to the tail rotor head. Examination of the main gearbox confirmed continuity from both inputs to the main rotor head, tail takeoff drive, and accessory pads on the rear cover.

Further examination of the main transmission revealed that the left input free wheel unit turned and freewheeled, but made a grinding noise when turned in the freewheel direction. Further examination of the left input free wheel unit revealed the gear housing was worn, with numerous roller impressions. The rollers were also rough in surface appearance. The right input free wheel unit operated in both directions without making any detectable noise. No detectable wear in the gear housing or the rollers was noted. The IFWU camshafts revealed a light wear marks. Both freewheeling units were recovered for further examination.

Examination of the left engine revealed that the engine was fire damaged. There was front-end damage to the engine. There was no evidence of any rotating part uncontainment. The power turbine was observed to turn freely when rotated through the input drive shaft. The input drive shaft, which connects to the main transmission gearbox, appeared slightly bent when rotated. The gas generator could not be turned through the started drive input.

Examination of the right engine revealed that the engine was fire damaged. There was no evidence of any rotating part uncontainment. The power turbine was observed to turn freely when rotated through the input drive shaft. The input drive shaft, which connects to the main transmission gearbox, appeared slightly bent when rotated. The gas generator also turned freely when rotated through the starter drive input.

MEDICAL AND PATHOLOGICAL INFORMATION

The office of the chief medical examiner, Tennessee Department of Health, performed the pathological diagnoses of the pilot on March 23, 2003. The cause of death was blunt force trauma. The Forensic Toxicology Research Section, Federal Aviation Administration, Oklahoma City, Oklahoma performed postmortem toxicology of specimens from the pilot. The results were negative for carbon monoxide, cyanide, and ethanol. Quinine was detected in the blood, and present in the liver.

ADDITIONAL INFORMATION

Examinations of the input free wheel unit assemblies were conducted at the Sikorsky M&P Technology Laboratory in July 2003. It was reported that the time since overhaul on the components was 960 hours. Sikorsky recommends free wheel unit time between overhaul of 350 hours. The material lab examination discovered the following:

1. Wear marks were found on the left hand side cam flats, gear housing roller path, and rollers. The wear patterns on the gear housing roller path and rollers showed evidence of roller "skidding". (According to Sikorsky the word skidding refers to a more gross condition of sliding in the contact, as in the case where a rolling element fails to maintain epicyclic speed of rotation for more than just an instant.)

2. The left hand side roller retainer had indentations. Along the forward inside diameter, indicating contact with the edges of the cam, which may be associated with cage misalignment due to Oilite™ bushing wear.

3. The left hand side aft Oilite™ bushing was found to contain numerous radial cracks intersecting the inside diameter.

4. Destructive metallurgical examination of the left hand side camshaft in a cam flat area, gear housing in a roller path area, and two rollers selected at random, indicated conformance to composition and hardness requirements.

5. The regions directly under the worn working surfaces exhibited white layers and metal flow appearances.

6. Non-destructive surface hardness tests indicated conformance to case hardness requirements on the right hand side cam shaft and gear housing, and conformance to the through-hardened requirement on two randomly selected right hand side rollers.

7. The right hand side gear housing and roller retainer both contained "Rotair" part markings. "Rotair" is not a Sikorsky-approved supplier. The left hand side roller retainer did not have any manufacturer markings.

8. Accumulated sludge-like material found inside both of the gear housing was found by FTIR analysis to contain evidence of Mobil 27 grease, which is not allowed in the subject gearbox.

9. Components from both the left hand side and right hand side free wheel units encompassing both camshafts, gear housings, and roller retainers, were magnetic particle inspected, with no cracks found.

The review of FAA-H-8083-21 Rotorcraft Flying Handbook, section Height/Velocity Diagram states that: the critical combinations of airspeed and altitude should an engine failure occur. Operating at the altitudes and airspeeds shown within the crosshatched or shaded areas of the Height/Velocity diagram may not allow enough time for the critical transition from powered flight to autorotation. The helicopter operated about 150 feet above the ground inside the shaded area of the Height/ Velocity Curve.

NTSB Probable Cause

The interruption of rotor system drive power due to the input free wheeling unit malfunctioning , and the pilot's operation of the helicopter in the critical area of the height-velocity curve.