TUCSON, AZ, USA
N6187C
Hughes OH-6A
The pilot was on short final approach to land when he reported an engine failure. He attempted to stretch his glide to avoid buildings and cars on the ground; however, the helicopter struck railroad tracks next to the field boundary. Damage to the main rotor blades was consistent with a low rotor rpm at impact. The pilot did not recall how much time had elapsed since his last refueling. Examination of the navigation and fuel endurance log from the helicopter cockpit (required by the operator) showed the pilot had not completed the fuel endurance calculations at the time of last fueling. The helicopter was equipped with a main fuel system and an auxiliary fuel system. A deferred maintenance item, 'main fuel gauge unreliable in forward flight,' was still open. The same discrepancy had also been entered previously and it, too, had not been cleared. The auxiliary fuel gauge was entered as inoperative on the deferred maintenance log with 'parts on order' but had not been cleared at the time of the accident. The pilot last recalled reading approximately 78 pounds on the main fuel gauge. He did not recall seeing the 20-minute light illuminate before the accident. A check of the low fuel warning system found that float arm contact in the fuel cell occurred at 34 pounds, which approximates 20 minutes of usable fuel; no discrepancies were found in the operation of the system. No evidence of a fuel spill was found around or under the wreckage. The crashworthy main fuel cell was uncompromised and about 12 ounces of trapped fuel was found. No fuel was found in the auxiliary fuel tank. The light bulbs for the 'Engine Out, Fuel Low, and Master Caution' were removed for examination. One 'Master Caution' bulb showed a small amount of filament stretching, consistent with hot stretching from a light to moderate impact force. The filaments of both 'Fuel Low' bulbs were intact and unstretched, consistent with bulbs not being illuminated during a light to moderate impact. The filaments from both 'Engine Out' bulbs showed a small amount of stretching, again consistent with hot stretching from light to moderate impact. There were no other discrepancies found with the engine or engine-related systems.
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 did not show rotational scoring. The blue blade exhibited minor trailing edge damage. The anti-torque control pedal assembly was torn out; the right side assembly was fractured at fuselage station 44. The control rod that is located under the center seat was pinched due to structural crushing. The tunnel routed control rod at fuselage station 78.50 was fractured at the lollipop bearing. The full movement of the collective control was restricted due to crushing of the surrounding structure. The collective control rod was fractured about 12 inches below the mixer assembly. The N2 governor linkage, the rod from the beep actuator to the bellcrank, was fractured at fuselage station 124. The proper rigging of the N2 governor linkage could not be verified due to impact damage. The N1 collective control linkage was separated between the pilot's twist grip throttle and the gas producer fuel control. Damage was also noted between the control rod from fuselage station 124 and the gas producer fuel control. The attach points on both cyclic trim actuators were fractured. The longitudinal control rod was bent at its lower end. The pilot's lateral control rod connecting to fuselage station 67 was separated at the forward lollipop bearing. The lower longitudinal bellcrank was fractured at fuselage station 78.5. The lateral control rod remained attached but was bent at the bottom. The main transmission assembly turned freely when rotated by hand. On June 16, 1999, investigators visually inspected the exterior of the engine. Due to the extent of damage to the engine, a system vacuum check could not be performed. The right engine mount remained attached; however, the lower leg was bent about 60 degrees. The vent system was crushed upward into the center lower fuselage. The igniter lead was separated from the igniter plug, and the starter-generator was separated from the gearbox-mounting flange. The No. 6 and 7 external sump cans were crushed. The lower magnetic plug head and the connector head were both separated. The fuel pump was separated from its mounting flange. The fuel outlet line was separated from the fuel pump; however, the line remained attached to the fuel control unit and the B-nut was secure in the pump inlet. The compressor discharge line from the power turbine governor to the pump and the attaching line to the turbine oil inlet check valve were both deformed. The fuel pressure line was deformed at the connection of the horizontal fire shield with the fuel nozzle. The outer combustion case and horizontal fire shield were crushed and buckled in an upward direction. The tunnel area of the turbine exhaust collector was twisted. The freewheeling unit was separated on the transmission side of the diaphragm. The fuel control unit was partially separated from the mounting flange at the location of one ear; in addition, there was a hole in the housing body. The control linkage exhibited impact damage. The fuel shutoff valve was found fractured and in the open position. The control line was pulled out of the console and pinched preventing it from being moved. The N1 and N2 systems would not rotate; however, there was no evidence compressor separation or foreign object damage and the compressor case showed no evidence of internal distress. The initial attempt to hand-rotate the compressor section was unsuccessful. Disassembly disclosed evidence of longitudinal crushing and bending on the shaft but there was no evidence found of improper assembly, improper parts, or unusual wear or coloration signatures. On June 17, 1999, investigators witnessed an engine disassembly conducted by factory-authorized personnel at Aircraft Services International, in Scottsdale, Arizona. Investigators noted that the outlet line from the fuel control unit to the fuel pump contained about 1 cc of residual fuel. The flex line from the horizontal fire shield to the fuel nozzle contained no fuel. The fuel pump filter bowl was dry. A disassembly of the fuel pump revealed that the pump drive shaft had fractured, and that two out of three mounting flanges were broken. After removing the turbine section, the N1 section could be turned freely through the accessory gearbox to the compressor without any discernable binding. The N2 section remained fixed due to crushing with the exhaust collector. The N2 accessory gearbox rotated freely through the output shaft. The accessory gearbox oil drained in a continuous flow. The plastic inlet plenum was fractured. The gas producer and power turbine sections were removed and revealed a light case rub along the blade path. The power turbine disassembly revealed that the No. 5 bearing was oil wetted and had no visual damage. The fourth stage blade path had rub indications encompassing 120 degrees of the circumference of its path with corresponding rub marks on the inner and outer rim faces. The gas producer disassembly did not reveal any abnormalities. The No. 8 bearing sump area was oil wetted and the bearing had no visible damage. The No. 6 and 7 sump areas and bearings were oil wetted and the corresponding bearings had no visible damage. The No. 5 bearing was oil wetted and carboned. The outer combustion case surfaces were buckled and deformed. MEDICAL AND PATHOLOGICAL INFORMATION The pilot received multiple severe traumatic injuries and was sedated immediately upon his admission to the hospital. No toxicological samples were obtained. Work environment temperature routinely exceeds 100 degrees Fahrenheit during the day throughout the summer months. The mission of pilot requires that most flights be conducted at contour elevations or below, over low desert terrain, and below cruise airspeed. The reported temperature at the time of the accident was 97 degrees. The helicopter is not airconditioned. Pilots routinely carry canteens of water and soak scarves that are then wrapped around their necks in an effort to cool down. SURVIVAL ASPECTS Rescue personnel found the pilot in the forward right seat with his 4-point restraint system still fastened. He was tangled in the cockpit wreckage, and due to this and his injuries, was unable to exit the helicopter w
Fuel exhaustion resulting from pilot's failure to perform adequate fuel consumption calculations. The unreliable and inoperative fuel level indicating system components and the operator's operation of the aircraft with known deficiencies were factors in the accident.
Source: NTSB Aviation Accident Database
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