N6187C

HISTORY OF FLIGHT

On June 15, 1999, at 1335 hours mountain standard time, a Hughes OH-6A, N6187C, crashed during the landing approach at Tucson, Arizona. The aircraft was destroyed and the commercial pilot, the sole occupant, received serious injuries. The U.S. Border Patrol was operating the aircraft as a public-use flight when the accident occurred. The flight originated from the Sells Airport, Sells, Arizona, at an undetermined time on the morning of the accident. Visual meteorological conditions prevailed at the time and no flight plan was filed.

The Federal Aviation Administration local controller at the Tucson International Airport Air Traffic Control Tower (ATCT) had cleared the helicopter for landing on runway 3 and had instructed the pilot to hold short of runway 11L when the pilot reported an engine failure. Based on witness accounts and impact ground scars, the estimated magnetic heading at the time the emergency occurred was between 70 and 80 degrees with the helicopter descending through about 200 to 300 feet agl. Witnesses described the forward airspeed as beginning to slow below 80 knots with an estimated descent angle of between 30 and 40 degrees and a greater than normal rate of descent.

According to witness observations, the pilot attempted to stretch his glide to avoid several buildings and cars; however, the helicopter struck a railroad track that runs along the west side of the airport perimeter. A witness stated that she saw the tail boom of the helicopter rebound into the air following contact with the tracks and then the helicopter spun counterclockwise about 170 degrees before finally coming to rest.

PERSONNEL INFORMATION

The pilot was a full-time employee of the United States Department of Justice, uniformed Border Patrol division. He held the position as a helicopter pilot since 1987. He was permanently based in Santee, California, and had been detailed to the Tucson office for about a month prior to the accident. His last flight check, a biennial flight review, conducted by the U.S. Border Patrol, was given on December 4, 1998, with no discrepancies noted.

The pilot holds a commercial pilot certificate with ratings for helicopter and airplane single engine land and instrument that was issued on September 10, 1982.

His second-class medical certificate issued on June 16, 1998, stated that he "shall have available glasses for near vision." He was wearing them at the time of the accident.

AIRCRAFT INFORMATION

Refueling slips indicated that the pilot had landed and refueled twice at Sells since his initial takeoff from Tucson earlier that morning. The pilot recalled only flying "about 6 hours" the day of the accident. He also recalled taking off "about 0730" that morning.

Review of the flight planning and fuel consumption logs in the helicopter revealed that he did not compute an estimated fuel endurance log after his last refueling.

Hughes Aircraft manufactured the helicopter, serial number (S/N) 68-17154, in 1968 as an OH-6A for use in aerial observation and scouting by the U.S. Army. The U.S. Border Patrol obtained the helicopter from military surplus for use in aerial observation as well. Since the date of manufacture it has accumulated a total of 7,177.1 flight hours.

After obtaining the helicopter, the Border Patrol maintained the helicopter on a continuous airworthiness maintenance program, having completed a 300-hour inspection on April 26, 1999, a 25-hour inspection on May 11, 1999, a 100-hour inspection on May 22, 1999, and a 50-hour inspection on June 7, 1999.

The Allison 250-C20B engine, S/N CAE836918, had last been removed, repaired, and tested, and then reinstalled on August 27, 1998, at a total time of 713.5 hours. The removal and repair was due to an N2 lockup with metal found in the engine oil. At the time of the accident, the engine had accumulated a total of 1,338.3 hours.

Review of the maintenance records disclosed that two of the life limited components, the fuel control, S/N 333703, and power turbine governor, S/N 3423R, did not list total times on the engine assembly record.

A deferred maintenance item, "main fuel gauge unreliable in forward flight," was entered on January 7, 1999, and was still open. The same discrepancy had also been entered previously on September 18, 1998, and it had not been cleared. The auxiliary fuel gauge was entered as inoperative on October 11, 1996. This discrepancy showed an entry for "parts on order" but had not been cleared at the time of the accident. According to the pilot's statement, he last recalled reading approximately 78 pounds on the main fuel gauge immediately prior to the engine failure.

The helicopter was equipped with a 50-gallon auxiliary fuel system.

The fueling log for the first flight of the day, June 15, 1999, showed that 58 gallons of JP-8 had been dispensed with 418 gallons remaining. Subsequent fueling slips indicated that an additional 50 gallons and 88 gallons were added later during the same day. The accumulated flight times at the time the refueling events occurred were not available.

The helicopter was not equipped with an auto relight system.

COMMUNICATIONS

The pilot contacted the Tucson ATCT operator on tower frequency 118.3 kHz after being handed off by Tucson approach control at 1330:23. The helicopter was issued a discrete transponder beacon code of 0424, and the pilot had radioed approach control that he had information Charlie on his initial call. All prior radio communications were described as routine with no sense of urgency reported.

At 1330:47 the pilot radioed "Tucson Tower, helicopter 6187C coming up on Black Mountain, 3,000, landing Border Patrol." At 2035:33, the operator instructed the pilot to "Okay, you can [air] taxi up to hold short of 11L. I have F-16's turning short final, landing runway 11L." The tower transcript revealed that, 7 seconds later, at 1335:40, the pilot radioed, "Emergency, I just had an engine failure." There were no subsequent radio transmissions from the pilot.

WRECKAGE AND IMPACT INFORMATION

Safety Board investigators found that the helicopter had impacted on the Southern Pacific railroad tracks that parallel the airport perimeter fence west of the airport property, east of the 7500 block of South Nogales Highway, and just a few feet north of the extended centerline for runway 03. The coordinates were 32 degree 06.983 minutes north and 110 degrees 57.588 minutes west.

Scratches found at the initial point of contact on the railroad tracks were oriented on a magnetic bearing of 075 degrees. The final bearing of the helicopter at rest was about 265 degrees and was about 20 feet further east of the first evidence of ground contact. All portions of the helicopter were found in the immediate area of the wreckage with the exception of the main cabin doors, which had been removed prior to flight.

The majority of the fuselage damage, including the keel beam, was represented by vertical crushing and lateral cracking. The skids were separated from the cross tubes. Both skids and cross tubes were crushed and bent, being partially separated from the helicopter. The structure beneath the pilot's seat was crushed downward about 5 inches. The pilot's seat frame exhibited multiple fractures.

The fuel system incorporates the military's crashworthy design featuring breakaway, self-sealing fuel fittings. Several fuel lines had separated; however, there was no evidence of a fuel spill nor was there any odor of jet fuel detectable. The main fuel cell was torn out of the center section of the lower fuselage; however, the fuel cell remained uncompromised. The non-crashworthy auxiliary fuel tank exhibited a tear but there was no evidence of fuel either inside or outside the tank.

When the forward and main fuel cells were opened, trapped fuel was found. The fuel was drained from both cells and collectively measured as about 12 ounces. There was no visual evidence of fuel contamination and the color and odor were consistent with jet fuel. According to the Hughes OH-6A flight manual, fuel levels less than 0.7-gallons are not useable.

Two fuel gauges are located on the control console. The main gauge read "0" on a face that reads from 0 to 356 pounds. The auxiliary gauge read "1/16" on a face that reads from E to F with 15 tick marks evenly spaced between the letters.

All four main rotor blades; green, white, blue, and red, were found attached to their respective blade grips. Based on ground scars at the accident site, there was no evidence found that any main rotor to ground contact occurred before the initial impact.

The white blade exhibited a 10-degree downward bending at the root fitting doubler. The blue blade exhibited a chordwise upward bending at blade station 93. The yellow blade exhibited a chordwise upward bending and buckling at blade station 105. The red blade exhibited 10-degree downward bending at the root fitting doubler.

According to the manufacturer, lower trailing edge damage predominated consistent with maximum pitch at impact. Conversely, leading edge blade damage was primarily cosmetic. There was no evidence of main rotor contact with the tail boom.

The green blade upper flapping stops exhibited damage. No such evidence was noted with the remaining three blades. There was no damage noted with any of the eight lead and lag links.

The green and blue main rotor dampener plungers were pulled out.

The blue main rotor feathering bearing studs exhibited a housing fracture. The blade striker plate was found rotated about 10 degrees out of its proper position. The blue upper feathering lug was fractured. The main rotor hub assembly turned freely when rotated by hand.

The tail boom remained attached to the fuselage though it was bent downward and cracked at fuselage station 170. Evidence of crushing was noted on the lower stabilizer. The red tail rotor blade was bent but ...