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Launched Aug 26 1996.

  This set consists of three documents:

Summary NTSB report:
Full narrative NTSB report
Paper describing reinvestigaiton

  Draw you own conclusions from reports in this set, and other examples in this section.


 

Accident AUG-13-94 at PEARBLOSSOM, CA
Aircraft: LOCKHEED C-130A, registration: N135FF
during wildfire 0perations

 

NTSB Identification: LAX94FA323. The docket is stored in the (offline) NTSB Imaging System.

Accident occurred AUG-13-94 at PEARBLOSSOM, CA
Aircraft: LOCKHEED C-130A, registration: N135FF
Injuries: 3 Fatal.

WITNESSES SAW THE AIRCRAFT IN LEVEL FLIGHT AND OBSERVED A BRIGHT ORANGE FLASH NEAR THE WING ROOT. THE FIRST FLASH WAS FOLLOWED ABOUT 1 SECOND LATER BY A MUCH LARGER DARK ORANGE FIREBALL AND BLACK SMOKE. THE RIGHT MAIN WING THEN SEPARATED FROM THE AIRCRAFT. THE WRECKAGE WAS DISTRIBUTED OVER 1 MILE IN MOUNTAINOUS TERRAIN. UNBURNED CENTER WING BOX SKIN, FOAM INSULATION PIECES, AND AUX TANK FRAGMENTS (ALL FROM THE AREA WHERE THE FIRST FLASH WAS OBSERVED BY THE WITNESSES) WERE THE FIRST DEBRIS FOUND IN THE WRECKAGE DISTRIBUTION PATH. THE DRY BAY AREA OF THE RIGHT WING CONTAINS HIGH PRESSURE FUEL LINES, UNSHIELDED AND EXPOSED ELECTRICAL WIRING, AND IS IN CLOSE PROXIMITY TO THE NO. 3 ENGINE. THE MAIN FUEL TANK IS LOCATED OUTBOARD OF THE DRY BAY. NO LIGHTNING ACTIVITY WAS REPORTED IN THE VICINITY OF THE AIRCRAFT. C-130 AIRCRAFT HAVE A HISTORY OF FUEL LEAKS IN THE DRY BAY. THE SOURCE OF THE LEAKS, FLATTENED OR PINCHED O-RINGS, ARE ON-CONDITION REPLACEMENT ITEMS. THE AIRCRAFT WAS IN LONG TERM STORAGE IN THE DESERT FOR 2 YEARS PRIOR TO ACQUISITION BY THE OPERATOR FOR FIRE TANKER DUTIES. U.S. AIR FORCE EMERGENCY PROCEDURES WARN OF FUEL LEAKS IN THIS AREA AND REQUIRE INSPECTIONS PRIOR TO EACH FLIGHT.
Probable Cause
the ignition of fuel leaking from the pressurized fuel system lines in or adjacent to the No. 3 dry bay, most likely due to electrical arcing and/or hot surfaces in the No. 3 engine.


LAX94FA323

HISTORY OF FLIGHT

On August 13, 1994, at 1331 hours Pacific daylight time, a civilian Lockheed C-130A, N135FF, operating as Tanker 82, crashed in steep mountainous terrain near Pearblossom, California. The aircraft was destroyed and the crew of three received fatal injuries. The aircraft was owned by Aero Firefighting Service Company, Inc., and was operated by Hemet Valley Flying Service, Inc., on lease to the U.S. Forest Service as a public use aircraft. The flight originated from Hemet-Ryan airport at 1310 on the day of the accident. Visual meteorological conditions were prevalent at the time of the accident and a company flight plan was filed for the operation.

According to the U.S. Forest Service personnel, the aircraft was responding to a fire near the Tehachapi Mountains at the request of the California Department of Forestry. The aircraft was flight following with High Desert TRACON (Joshua approach control) and its encoding altimeter was indicating 7,800 feet msl. A review of air traffic control communication tapes revealed two unidentified transmissions; one of an unintelligible squeal, followed by a brief expletive at 1331.

Witnesses in the vicinity of the San Gabriel Mountains reported seeing the aircraft in level flight, on a west-northwesterly heading, when they saw a bright orange flash near a wing root. The first flash was reportedly followed about 1 second later by a much larger, darker orange fireball accompanied by black smoke. At that time, witnesses stated that the main wing separated from the aircraft and the aircraft began to roll. Both the separated right wing and remaining fuselage impacted on the north face of Pleasant View Ridge in the vicinity of Pechner Canyon at about the 6,500 foot level.

Witnesses stated that the ground impact of the main wing and fuselage resulted in an additional fireball and explosion with a column of black smoke, causing several small brush fires. At least one witness stated that the smoke from the ground fire rose vertically in an undisturbed column. Individual witness statements are attached to this report.

PERSONNEL INFORMATION

The pilot, copilot, and flight engineer were rated in the aircraft. A review of the pilot/operator accident report prepared by the operator showed the crew had current flight experience in the accident aircraft. According to FAA inspectors, at the time of the accident, the flight was being operated in accordance with applicable FARs.

AIRCRAFT INFORMATION

The aircraft was delivered to the U.S. Air Force in December, 1957. In April, 1959, it was modified to become a C-130A-II to perform an electronic reconnaissance mission. In September, 1964, it was de-modified and reconfigured to a "near standard C-130A" and transferred to the Air National Guard. In August, 1986, the aircraft was transferred to Davis-Monthan Air Force Base for storage. In June, 1988, the aircraft was removed from storage. In June, 1990, modification as a restricted category firefighting aircraft was approved per FAA Form 337. A Restricted Category Special Airworthiness Certificate, which authorized aerial dispensing of fire retardant, was issued in May, 1990.

A review of aircraft maintenance records revealed that on April 22, 1994, the aircraft had been returned to service after an entire progressive inspection cycle. The inspection program was an FAA approved and authorized airplane inspection program (AAIP). The aircraft had completed an eddy current inspection in April, 1991. All parts tested met the inspection standard. Investigators estimated that at the time of the accident, the aircraft was within weight and balance limitations and had sufficient fuel to complete the planned flight. An FAA review of the maintenance records and the Hemet Valley Flying Service Return to Service Inspection are appended to this report. On July 17, 1994, (the most recent record available) the operator completed a Day Off Inspection (seven day checks), which included the initialed item No. 20 b, "Check dry bay area for leaks, fuel press. on." The records of subsequent checks were onboard the aircraft and were destroyed. The Hemet Valley flying Service Day Off Inspection is attached to this report.

METEOROLOGICAL CONDITIONS

According to a readout from the Bureau of Land Management's Automatic Lightning Detection System (ALDS), there was lightning activity in the area of the accident site at the time of the crash. Witnesses both on the ground and in the air near the accident site reported that the aircraft was clear of clouds and that there was no visible electrical activity at the time of the in-flight explosion. The NTSB weather factual report and the California Department of Forestry lightning strike analysis are attached to this report.

AIDS TO NAVIGATION

The aircraft was on a flight conducted under visual flight rules, and was flight following on frequency 124.55 with Joshua approach control at the time of the accident. The crash site was located along an imaginary line connecting the Hemet-Ryan airport and Tehachapi, California. At 1330, the pilot reported to Joshua approach that he intended to "go straight for the next 42 miles" when he was asked to say his destination. The assigned mission was to respond to a reported fire in the Tehachapi Mountains.

According to U.S. Forest Service officials, dispatch information includes magnetic direction to the fire and distance from the departure airport, along with the latitude and longitude of the fire's location. The operator reported that the crew was familiar with the area and that the aircraft was equipped with a global positioning system (GPS).

COMMUNICATIONS

After takeoff, the crew had initiated two-way radio contact with Ontario approach control for the purpose of flight following. The crew had been responding to radio calls without delay or difficulty until 1330 (about 1.5 minutes before the crash). All communications were routine with no indication of any in-flight problems. A transcript of radio communications is appended to this report.

WRECKAGE AND IMPACT INFORMATION

The structures group chairman report is attached to this report. A total of six center wing pieces, five of the upper wing surface and one piece of stringer, were found approximately 1,000 feet in advance of the separated main wing. Numerous pieces of 1-inch thick yellow styrofoam, a green interior wing panel, and a torn portion of a fuel cell liner were also found in the same general area. None of this debris had been involved in the resulting ground fire. The styrofoam material was reported to have been located beneath the auxiliary fuel cell. Portions of the styrofoam exhibited evidence of surface charring. Light sooting of the wing pieces was consistent with normal service.

Crush on the separated right wing components indicated a near- level attitude at impact. The identification was made by serial numbered components recorded as being located on the right side of the aircraft. Examination of the debris showed the outline of a burned and melted main wing structure extending from the right wing tip to a section inboard of the No. 3 engine nacelle. The ground fire had melted or consumed all fracture surfaces on the inboard portion.

The powerplant group chairman report is appended to this report. A tear down inspection of the No. 3 and 4 engines showed no evidence of rotational scarring. Although the supporting structure was fractured or consumed by fire, the engines still maintained their relative positions on the right wing. The persistent odor of ammonia was detected in and about the No. 3 engine.

Both the No. 3 and 4 propellers and hubs were found separated from the engines. The No. 3 propeller was found in the feathered position while the No. 4 propeller was found in reverse. There was no bending, twisting, or leading edge damage on any blade from either the No. 3 or No. 4 hubs. Two blades from the No. 3 hub had been consumed by fire up to the blade root.

The main fuselage and remaining left wing impacted a rising terrain finger. The impact resulted in major structural collapse and disintegration, and was accompanied by postcrash fire.

The cockpit area was identified, but efforts to access the interior portion were unsuccessful. Attempts at an aerial recovery of the cockpit were also unsuccessful and resulted in disintegration of the structure.

The No. 1 and 2 engines were recovered and both exhibited evidence of rotational scarring. Both engines were displaced from their position relative to the left wing. Crush on the engine cases indicated a near 90-degree terrain impact angle on both engines.

The No. 1 and 2 propellers and hubs were separated from the engines. None of the No. 1 or 2 propeller components were recovered.

MEDICAL AND PATHOLOGICAL INFORMATION

No autopsy or toxicological examination was performed on any of the aircraft crewmembers.

FIRE

Witnesses reported an in-flight explosion and fire. The accident was followed by a postcrash fire, which involved the separated right wing and the remainder of the aircraft. Firefighting helicopters responded to the accident site, dumping water directly on the wreckage and surrounding area. In spite of those efforts, the wreckage continued to smolder for over 24 hours.

TESTS AND RESEARCH

Lockheed reported that in 1978, a C-130A experienced an in-flight fire and explosion, which resulted in a wing separation due to a lightning strike on a fuel probe.

A section of the center wing section which was found early in the debris path, was submitted to the Materials Directorate at Wright-Patterson Air Force Base for analysis. Examination disclosed no evidence of a lightning strike. None of the fuel probes from the accident aircraft were identified or recovered. The USAF analysis of C-130A wing section and NTSB Metallurgist's factual report are appended to this report.

The U.S. Air Force reported that the fuel systems in C-130A aircraft have experienced fuel leaks due to O-ring failure. The Air Force does not track the rate of O-rings failures associated with the fuel system. Lockheed engineers confirmed that report, saying that while O-ring failure is a relatively rare event, it does occur. According to the Air Force, there have been no known C-130A accidents in which an external fuel leak was determined to be the probable cause. Fuel system schematic drawings are attached to this report. According to Lockheed, failures that have occurred were the result of fuel line flexing or thermal expansion. They reported that a failure is more likely to occur in a fuel line coupling as opposed to a fuel valve, although the possibility exists for both. They stated that an O-ring failure can range from seeping or dripping occurring over time, up to a failure that results in a sudden a high pressure spray. They expressed the opinion that prolonged storage (such as occurred at Davis-Monthan Air Force Base from 1986 to 1989) could result in the O-rings drying out or shrinking. They also acknowledged that the flight profile of aerial firefighting results in wing flexing. A review of maintenance procedures, followed by both the U.S. Air Force and the operator and confirmed by Lockheed, revealed that O-rings are an on-condition item and are not life limited. Lockheed did report that once O-rings are removed, they are not to be reused. A review of maintenance records of the accident aircraft did not identify any reported fuel leaks or the removal or replacement of any fuel line, coupling, or valve. According to the operator's records, an inspection of the fuel system was completed on April 22, 1994. The operator reported that an item on the preflight inspection of the aircraft specifies checking the dry bay for fuel odor. Emergency procedures contained in T. O. 1C-130A-1 and the top of aircraft inspection check list are appended to this report.

The fuel system of the C-130A is pressurized to 15-17 psi for the lines that transfer fuel from the main fuel tanks to the engine. Cross-feed lines that transfer fuel from the main tanks in the opposite wing are pressurized to 15-17 psi when utilized. The fuel valves in the C-130A operate on a 28-volt DC current single phase circuit. The valve motors are powered only when the valves are in transit to open or close; however, the cannon plugs are powered whenever DC power is energized. The external cannon plugs on the valves are not shielded. The electrical wiring is open within the corresponding wing section and is in proximity to the fuel system. Lockheed reported that there has been some history of insulation chaffing or cracking, but did not report any known incidents or accidents in which an electrical short had contributed to a fuel-fed fire. U.S. Air Force T.O. 1C-130A-1 states that external fuel leaks present a fire hazard if the leak is in the proximity of an engine. If a leak occurs, it is recommended that an emergency be declared and that the aircraft land at the nearest airfield with sufficient runway to complete the landing roll without use of reverse thrust. Lockheed reported that with sufficient fuel leaking in the dry bay it would be possible for fuel to drain through the engine pylon and into the engine nacelle. The hot section of the No. 3 engine is located below the No. 3 dry bay. The tattletale drain for the dry bay exits out of the lower engine nacelle forward of the hot section.

The fuel used in the aircraft, Jet-A1, has a flash point of 40 degrees centigrade (100 degrees Fahrenheit) according to a publication by the U.S. Air Force Systems Command at Wright- Patterson Air Force Base, Ohio.

ADDITIONAL INFORMATION

The wreckage was released to a representative of the U.S. Forest Service on October 17, 1995.