N6156U

HISTORY OF FLIGHT

On August 4, 2006, at 1947 Pacific daylight time, an Aviation International Rotors CH-54A, N6156U, was substantially damaged when it impacted terrain following an in-flight separation of a tail rotor blade while maneuvering near a dip site near Happy Camp, California. The Department of Agriculture (USDA), U.S. Forest Service (USFS) was utilizing the helicopter under contract as a public-use firefighting tool [heli-tanker (HT) 790] under the provisions for 14 CFR Part 91. The helicopter was registered to Heavy Lift Helicopters Inc. (HLH), of Apple Valley, California, and the flight crew was employed by HLH. The airline transport pilot (ATP) captain and ATP co-pilot both sustained fatal injuries. Visual meteorological conditions prevailed and a USFS flight plan was filed. The flight was receiving flight following from the USFS dispatch personnel at the time of the accident.

The helicopter was flown to the Happy Camp Complex in Happy Camp, California, on July 29, 2006, to help suppress the Titus Fire. The helicopter was stationed at the Happy Camp helibase where it was maintained and dispatched.

On the morning of the accident, the helicopter went through a series of maintenance and flight tests after having its number 1 engine replaced the night before. The helicopter was returned to service at 1645 by the HLH mechanics and the USFS helicopter manager. The helicopter was then dispatched to the Titus fire where it conducted a number of water drops. After 2.2 hours of flight (at 1902), the helicopter returned to the helibase where it was refueled with approximately 500 gallons and examined by maintenance personnel. The helicopter departed for a second cycle of water drops at 1912 and never returned to the helibase.

The satellite tracking system that the USFS utilizes to provide real-time data on their flights indicated that the helicopter filled its water tanks at a dip site located in the Klamath River near the Independence Bridge. The helicopter conducted one uneventful dip and water drop during the second cycle and was in the process of conducting its second dip when the accident occurred.

A witness located near the accident site reported that he observed the helicopter come in and out of the same dip site that day filling the helicopter's water tanks. The helicopter was located over the dip site when the witness heard a "loud bang." He realized something was wrong with the helicopter and ran down his driveway toward the road that paralleled the river. When he reached the road he observed the helicopter flying over a stone riverbed toward the Independence Bridge. He then noticed a large piece fall off the helicopter, which was later identified as the tail rotor gearbox with three of the four tail rotor blades attached to the hub. The helicopter pitched nose low at an approximate 45-degree nose down attitude while rotating around its vertical axis. The helicopter impacted the opposite side of the river/shoreline. The witness called the USFS over a radio to report the accident.

PERSONNEL INFORMATION

Captain

The captain held an airline transport pilot certificate with a multi-engine airplane rating, and a commercial pilot certificate with single-engine airplane, rotorcraft-helicopter, and instrument helicopter ratings. He was type rated in the SK-58, SK-61 and SK-64 helicopters. He also held a flight instructor certificate for single-engine, multi-engine, and instrument airplanes. He was issued a second-class medical certificate on December 23, 2005, with a limitation for corrective lenses.

According to the operator's records, the pilot accumulated over 14,000 hours of total flight time. Of those, about 11,210 hours were accrued in helicopters and 4,212 hours were flown in the same make and model as the accident helicopter.

Copilot

The copilot held an airline transport pilot certificate with a rotorcraft-helicopter rating. He was issued a second-class medical certificate on March 22, 2006, with no limitations or waivers.

According to the operator's records, the copilot accumulated about 4,700 hours of flight time in helicopters, of which 278 hours were accrued in the accident helicopter make and model.

AIRCRAFT INFORMATION

The helicopter was originally manufactured by Sikorsky for the U.S. Military as a CH-54A helicopter. The helicopter exited military service and entered civilian service under a restricted category. The type certificate for this model of the restricted category helicopter was then transferred to Aviation International Rotors. Review of the operator's instructions for continued airworthiness for the CH-54A revealed that maintenance/overhaul schedules and procedures were to follow the applicable military manuals. The tail rotor head assembly had an overhaul interval of 1,000 hours, which was to be completed per the Navy's NAVAIR manual 03-95B-106 (the June 1, 1984 version; change 3, dated August 15, 1988).

Review of the maintenance records, flight logs, and USFS daily diaries revealed that the helicopter accumulated a total of 6,191.6 hours on the morning of the accident. On December 22, 2005, the tail rotor hub assembly underwent its 1,000-hour overhaul, which included the fluorescent penetrant inspection of the spindle. The tail rotor hub assembly was installed on the accident helicopter at a total time of 5,958.0 hours, about 233.6 hours prior to the accident. The spindle was not a life-limited component, and therefore, it is unknown as to how many total hours the spindle had been in service.

The tail rotor has four blades on the left side of the helicopter that rotate clockwise (as viewed looking at the left side of the helicopter) about the tail rotor head assembly axis. Each blade is bolted to a sleeve and spindle assembly, which in turn is attached to the tail rotor hub with a shoulder bolt. The spindle is made of a titanium alloy, with 6 percent aluminum and 4 percent vanadium. The exterior of the spindle and sleeve assemblies are each painted a different color: red, blue, black, or yellow. The spindle serial numbers for the accident helicopter were as follows: red F-1560, blue F-308, black F-1938, and yellow FM400.

During assembly of the spindle group, a split ring is put in the center of three grooves (referred to throughout this report as the inboard, middle, and outboard grooves) located on the shank of the spindle. A spacer is then pushed over the spindle from its outboard end (in relation to the axis of rotation) until a step on the inside diameter of the spacer contacts the split ring. Sealant is then applied at the inboard end of the spacer, between the spacer and the spindle shank.

Review of the NAVAIR 03-95B-106 manual (under section 4-29, Shot-Peening) revealed that the spindle is to be fluorescent penetrant inspected and shot-peened at each overhaul. The shot-peening section indicated that bonded components, such as the spacer, are not to be removed during the overhaul unless they are damaged or do not meet the minimum service limits listed in the manual. According to the operator they did not remove the spacer that covered the split ring and the three grooves during each overhaul unless the spacer was beyond its approved limits.

WRECKAGE AND IMPACT INFORMATION

Review of the wreckage at the accident site revealed that the tail rotor gearbox (with three tail rotor blades attached) came to rest at a global positioning system (GPS) measured location of 41 degrees 39.707 minutes north latitude and 123 degrees 26.919 minutes west longitude. The helicopter fuselage, with its two engines, main rotor transmission, and main rotor hub attached, came to rest at a GPS measured location of 41 degrees 39.658 minutes north latitude and 123 degrees 26.895 minutes west longitude (separated from the tail rotor gearbox by approximately 500 feet). Sections of the tail boom were located in the river. The pylon, with the horizontal stabilizer and intermediate gearbox attached were located on the opposite bank from the fuselage.

Examination of the tail rotor system revealed that the blade associated with the red spindle was missing and has not been located at the time of this report's writing. The spindle (part number 65112-07002-047; serial number F-1560) was fractured inboard of where the sleeve assembly would attach to the spindle. The spindle fracture surface was flat in appearance and displayed arch-shaped marks that emanated from one of the edges through about half of the spindle material. It was noted that the location of the fracture would not normally be visible in an assembled component.

The fractured spindle was removed from the tail rotor hub and shipped to the NTSB Materials Laboratory in Washington, D.C. for further examination.

On November 16 and 17, 2006, the NTSB investigator-in-charge, along with representatives from the USFS and HLH examined the wreckage at Plain Parts in Sacramento, California. The examination resulted in verification of continuity through the #1 and #2 engine free turbines, main rotor transmission, and tail rotor drive shaft. In addition, continuity was confirmed through the intermediate and tail rotor gearboxes (both magnetic chip plugs for these gearboxes were free from ferrous debris). Two tail rotor drive shaft bearings were located in the retrieved wreckage. There were no anomalies noted with these two bearings. Six Thomas couplings were located in the wreckage. They were all warped to some extent with one being splayed and shredded.

Approximately 15 feet of tail boom remains missing along with sections of the tail rotor drive shaft, and the red tail rotor blade.

MEDICAL AND PATHOLOGICAL INFORMATION

Autopsies were performed on each pilot by the Siskiyou County Coroner's Office. Neither autopsy revealed any pre-existing medical condition that would have contributed to the accident.

Toxicological tests were conducted on each pilot by the Feder...