Walker, CA, USA
N130HP
Lockheed C-130A
The airplane was making a fire retardant drop over a mountain drainage valley when the wings separated from the fuselage. A videotape of the accident sequence showed the airplane as it flew down the valley and proceeded to make a fire retardant drop. When the drop was almost completed, the airplane's nose began moving up, and the airplane started to arrest its descent and level out. The nose of the airplane continued to rise, and the airplane's wings folded upward until they detached from the fuselage at the center wing box beam-to-fuselage attachment location. Close examination of the video revealed that the right wing folded upward first, followed by the left wing about 1 second later. Metallurgical examination of the center wing box lower skin revealed a 12-inch long fatigue crack on the lower surface of the right wing beneath the forward doubler, with two separate fatigue crack initiation sites at stringer attachment rivet holes (which join the external doubler and the internal stringers to the lower skin panel). The cracks from both initiation sites eventually linked up to create a single crack. The portion of the wing skin containing the fatigue crack was covered by a manufacturer-installed doubler, which would have hidden the crack from view and, therefore, prevented detection of the crack from a visual inspection of the exterior of the airplane. The investigation found that the airplane was probably operated within the maximum takeoff gross weight limits specified in the airplane flight manual. The airplane was delivered new to the U.S. Air Force (USAF) in 1957 and was retired from military service in 1978. The U.S. Forest Service (USFS) acquired it from the USAF in 1988 for use as a fire suppression tanker. Between 1978 and 1988, it was kept in a desert storage facility. It was transferred to a civilian contractor for firefighting operations and modified for that role, then sold to a Part 135 operator. The airplane was certificated by the FAA in the restricted category under a type certificate held by the USFS. A Lockheed study concluded that firefighting missions were substantially more severe than typical military logistics operations and aircraft operated in this role would require inspection intervals as much as 12 times more frequently than typical military transport usage for meeting damage tolerance requirements. Concerning the detectability of the cracks, Lockheed reported that nondestructive x-ray inspection methods in current industry and military depot level maintenance processes could have detected, with high confidence, the fatigue cracks when they were 0.50 to 0.75 inch long. Inspection intervals appropriate for this detectable crack size can be determined from a damage tolerance crack growth analysis; however, this requires an extensive knowledge of the operational loads environment and internal stresses of the C-130A wing such as would be found in a military depot level maintenance program. The operating limitations accompanying the restricted certificate specified that it be flown and maintained in accordance with the then-current (1988) USAF technical orders for the C-130A. The USAF depot level maintenance program was not included in the maintenance technical orders and was not individually specified on the certificate's operating limitations. The limitations letter did not specify compliance with USAF maintenance program modifications/amendments in technical orders issued after 1988. The operator devised a maintenance and inspection program based on the specified USAF maintenance technical order but did not develop a depot level inspection requirement to ensure continued long-term airworthiness and damage tolerance that would account for the stresses on the airplane resulting from its new firefighting role and the increasing age of the airplanes. Investigation found that there are five separate FAA-issued type certificates owned by five separate firms for the C-130As used as tankers. Although the five certificates have similar maintenance requirements, none are standardized, there is no depot level maintenance program specified for any of them, and none require full compliance with all military airworthiness technical orders. In 1991, the Department of Interior (DOI) began to doubt the continued airworthiness of the C-130A firefighting tanker fleet and was specifically concerned that the lack of a depot level maintenance program or any requirement for compliance with all military airworthiness technical orders could compromise the safety of the airplane. The DOI asked the FAA to standardize the type certificate for the C-130A and mandate improvements in the maintenance and inspection requirements. In a written opinion, the USAF agreed and urged the FAA to mandate that operators establish a depot level type continuing airworthiness program for the airplane and mandate compliance with all technical orders. In a series of meetings held in 1993, FAA management internally agreed that the DOI and USAF positions held merit and began to develop requirements. In late 1993, in a meeting between the FAA, DOI, USFS, and the airplane operators, the USFS and the operators objected to the idea of depot level maintenance programs and full compliance with all technical orders on the basis of the potential economic impact of these requirements. As of the time of the accident, the FAA had not standardized the existing five type certificates nor had they imposed any additional maintenance or inspection program requirements.
HISTORY OF FLIGHT On June 17, 2002, about 1445 Pacific daylight time, a Lockheed C-130A, N130HP, broke apart in flight while executing a fire retardant delivery near Walker, California. The airplane was registered to Hawkins and Powers Aviation, Inc., Greybull, Wyoming, and operated by the Department of Agriculture (USDA), US Forestry Service (USFS) under 14 CFR Part 91 for the public-use firefighting flight. The three flight crewmembers were fatally injured and the airplane was destroyed. Visual meteorological conditions prevailed, and a company flight plan had been filed. The airplane had departed Minden, Nevada, about 1429, to participate in firefighting efforts near Walker. The accident flight started with the airplane, using the call sign tanker T130, at the Minden Air Tanker Base for loading of fire retardant. According to the relevant Minden Air Tanker Dispatch/Flight Record sheet, tanker T130 was loaded with 3,000 gallons of fire retardant but no fuel was added. The airplane departed Minden at 1429, for its sixth drop of the day, and proceeded directly to the Cannon Fire located adjacent to Walker. Although the aircrew of tanker T130 had already made five previous drops on a north to south axis the day of the accident, the sixth drop was to be their first run on an east/west course. Prior to the run, tanker T130 made a pass over the drop area in the direction of the intended drop. The intended run required a course heading of approximately 90 degrees over and perpendicular to a ridgeline and down a steep drainage valley. A witness to the accident videotaped the accident sequence starting with T130 at the top of the ridgeline to a point after the wings had separated from the airplane. The following account of the accident sequence is based on the video footage. Tanker T130 flew down the east side of the drainage valley and proceeded to make a 1/2 salvo fire retardant drop. Just prior to the completion of the drop, the nose of the airplane appeared to rise and the airplane started to initially arrest its descent and to level out. The nose of the airplane then continued to rise towards a nose up attitude and almost at the completion of the 1/2 salvo fire retardant drop, the airplane's wings folded upwards and detached from the fuselage at the center wing box beam-to-fuselage attachment location. Close examination of the video revealed that the right wing folded upwards first followed slightly less than 1 second later by the left wing. After the wings separated, the fuselage continued to travel in the direction of the intended flight path, the nose pitched down, and the fuselage rolled to the right (clockwise) becoming inverted until the airplane was out of camera shot. Subsequent examination of the wreckage and the right wing disclosed evidence of fatigue cracks in the right wing's lower surface skin panel, with origins beneath the forward doubler at Center Wing Station (CWS) 53R at the stringers 16 and 17 location. The origin points were determined to be in rivet holes, which join the external doubler and the internal stringers to the lower skin panel. These cracks, which grew together to about a 12-inch length, were found to have propagated past the area where they would have been covered by the doubler and into the stringers beneath the doubler and across the lap joint between the middle skin panel and the forward skin panel. PERSONNEL INFORMATION First Pilot Information The pilot held an airline transport pilot certificate with single and multiengine land airplane ratings, rotorcraft helicopter and gliders limited to aero tow. His certificate was endorsed with type ratings for DC-6, DC-7, CY-P4Y, FA-119C, DC-826, L P2V, L-382 (the civil version of the C-130E). His most recent second-class medical certificate was issued on March 12, 2002, and contained no limitations. He also held a flight engineer certificate for turbo propeller powered airplanes and was a certificated airframe and powerplant technician. According to the Forestry Service Airplane Pilot Qualification and Approval Record, dated March 30, 2002, the pilot had recorded a total flight time of 10,833 hours, with 130 hours in the last 12 months. He was approved to fly C130A, P2V, and PB4Y2 aircraft. The form lists 1,790, 915, and 1,450 hours in the approved aircraft as listed. The pilot's last documented biennial flight review occurred on March 30, 2002, in a C130. Copilot Information The copilot held an airline transport pilot certificate with a multiengine airplane land rating. He also held certificates as an advanced ground instructor, an airframe and powerplant technician, and a flight engineer with a rating for turbo propeller powered airplanes. His certificate was endorsed with a type rating in the L-382, the civil version of the C-130E model. The copilot's most recent second-class medical certificate was issued January 23, 2002, and contained the limitation that corrective lenses be worn. The Forestry Service Airplane Pilot Qualifications and Approval Record, dated February 4, 2002, recorded a total flight time of 2,407 hours with 199 hours in the last 12 months. He was approved to fly the C-130, or perform the functions of a flight engineer in the C-130. The record documented 322 hours of flight time as pilot-in-command. The date of his last flight check was September 19, 2001. The copilot's last biennial flight review equivalent occurred on January 29, 2002. Flight Engineer Information This crewmember held a Flight Engineer certificate with ratings for jet and turbo propeller airplanes. In addition, he held a commercial pilot certificate with land airplane ratings for single engine, multiengine and instruments. He also held a Flight Instructor certificate with the same airplane ratings found on his commercial pilot certificate. Other certificates held were a ground instructor and a certificated airframe and powerplant technician. AIRCRAFT INFORMATION General Airplane History The USDA Forest Service promoted the transfer of military surplus C-130A airplanes to the contract fire tanker operators in an effort to update the fleet of airtankers to an all turbine fleet. After the USDA Forest Service facilitated transfer of an airplane, it became the operator's financial responsibility to prepare the airplanes for the airtanker mission. The operators then had to competitively bid for the contract at a low enough price to be awarded a year-long contract for fire suppression missions. According to statements from Forest Service contracting specialists, the monetary element of the bid may be the most critical in getting work for the airplanes because of Forest Service budget constraints. The accident airplane was delivered to the United States Air Force (USAF) in December 1957 as a Lockheed Aircraft Corporation C-130A Hercules, Air Force serial number 56-0538, Lockheed serial number 3146, and was retired from military service in 1978 and placed in storage at the Davis-Monthan Air Force Base near Tucson, Arizona. On May 24, 1988, the Forest Service acquired SN 56-0538, along with six other C-130A airplanes, from the General Services Administration (GSA). According to the a GSA transfer order dated January 1988, the airplane's total time was 19,546.8 hours time since new (TSN). On August 12, 1988, the airplane was sold by the USFS to Hemet Valley Flying Service, Hemet, California, along with five other recently acquired C-130A airplanes, for installation of retardant tanks. Hemet Valley applied for a US civil registration number of N134FF for airplane SN 56-538 on July 19, 1988, and subsequently sold it to Hawkins & Powers Aviation, Inc. (H&P), on December 5, 1988. In accordance with 14 CFR 21.53, on December 10, 1988, H&P prepared and presented to the FAA a Statement of Conformity, FAA Form 8130-9, for civil type certification of the airplane. This statement included a declaration that the aircraft, engines and propellers conformed to the type design, 14 CFR 21.33, and Type Certificate (TC) A15NM, revision 2. That same day, the company also applied to the FAA for a Special Airworthiness Certificate in the Restricted Category. On December 15, 1988, the FAA's Phoenix Manufacturing Inspection Satellite Office (MISO) issued H&P a Restricted Category Special Airworthiness Certificate in accordance with 14 CFR 21.185(b). In addition to the certificate, they also issued the accompanying Operating Limitations, which required that the airplane be operated in accordance with USAF Technical Order (T.O.) 1C-130A-1 (USAF Series C-130A airplane flight manual) and that the airplane must be serviced and maintained in compliance with USAF T.O. 1C-130A-2-1 through 1C-130A-2-13. On December 28, 1988, H&P applied for and was granted an aircraft registration number change from N134FF to N130HP. The FAA's Helena FSDO reissued a Restricted Category Special Airworthiness certificate for the airplane for the purpose of Carriage of Cargo on August 8, 1989, with the same operating limitations. On June 1, 1998, the FAA's Flight Standards Field Office (FSFO), Casper, Wyoming, rescinded the August 8, 1989, Restricted Category certificate and associated operating limitations and issued a new Restricted Category Special Airworthiness Certificate for the following special purpose operations: agricultural missions, forest and wildlife conservation, aerial surveys, and any other type of operation approved by the FAA. Along with the new Special Airworthiness Certificate, the FAA also issued a new Special Operating Limitation sheet, which required compliance with all the same operational, service, and maintenance required USAF T.O's as previously required, but also added a requirement that the company use a self-developed maintenance document entitled "H&P-C-130A Inspection Guide." Airplane Operating Limitations The FAA approved operating limitations for the airplane were based on two documents, one the original US Air Force flight manual, T.O. 1C-130A-1 (the Restricted Category certificate operating limitations required adherence to this document), and the supplemental operating limitations issued with the Supplemental Type Certificate for installation of the retardant tank and dispensing equipment. The original maximum-g load factor for the C-130A was +3.0 g/-1.0 g up to maximum level flight speed (Vh) at design gross weight (108,000 pounds); +2.0 g/-1.0 g up to maximum level flight speed (Vh) at maximum alternate gross weight (124,200 pounds). Operational limitations are defined in terms of gross weight and airspeed limits at 2.0g, 2.5g, and 3.0g missions in Figure 5-5 of T.O. 1C-130A-1. The maximum load factor on the FAA approved N130HP airplane flight manual is 2.5g based on the FAR Part 25 (25.337) and Car 4b. (4b.210) requirements. There are no structurally limiting factors for 2.5g. The maximum maneuver load factor regardless of cargo load, gross weight, or airspeed combination with any flap deployment was 2.0g; this is based upon the historical Military Specification (C-1803-E "Stress Analysis Criteria", dated June 17, 1949), which in turn defers to CAR 4b.212. Specifically, the flight manual cautions that "The maximum maneuver load factor, regardless of cargo load, with any flap extension is 2.0g." The event aircraft wreckage evidence indicated 50 percent flap extension. The flaps on a C-130A are considered secondary structure. Aircraft Weight and Balance Supplemental Type Certificate (STC) SA4835NM for the fire retardant tank installation requires a supplement to the Lockheed C-130A USAF Series Flight Manual T.O. 1C-130A-1. The FAA approved supplement for Hemet Valley Flying Service, dated January 30, 1990 specifies maximum takeoff gross weight and maximum zero fuel weight limits of 120,000 and 97,000 pounds, respectively. It also specifies that 617 pounds more fuel should be maintained in each outboard tank than in each inboard tank and requires placards on each retardant tank at each fill valve emphasizing a maximum capacity of 13,650 pounds. According to an H&P aircraft weighing record, dated June 17, 1999, the operating empty weight listed was 68,261 pounds, including unusable fuel and full oil. The most recent record is Hawkins and Powers Form #45, a weight and balance worksheet for serial #56-538 dated April 19, 2001. This worksheet contains itemized weights of 600 pounds for the 3 crew members including nominal baggage and 1,240 pounds for a flyaway kit (consisting of spare parts and other mission consumables). The operating empty weight as of April 19, 2001 was documented to be 67,928 pounds. Records indicate that the total flight time on the day of the accident was 3 hours 9 minutes and the aircraft logged six takeoffs, each time loaded with 3000 gallons of fire retardant. The density of the fire retardant is assumed to be 9 pounds per gallon. The retardant drop in progress just prior to the event was the first of two planned salvos. Repeated inquiries as to the actual retardant dropped just prior to wing separation returned consistent estimates of 13,500 pounds. Tanker T-130 reportedly refueled the night before the accident and did not take on any fuel on the day of the accident. The gross weight estimation assumed that 1) enough fuel was added on June 16, 2002 to bring N130HP to maximum takeoff gross weight with a full retardant load for the first flight of the day, 2) the flight manual supplement fuel management constraint of 617 pounds more fuel in each outboard tank than in each inboard tank was practiced, and 3) the outboard and inboard tank capacities were 1335 and 1190 gallons for a total fuel capacity of 5,050 gallons . The fuel consumption rate is 730 gallons per hour, which assumes that 1 takeoff, 2 climbs, 1 drop, and 1 landing occur during a one-hour mission. On the day of the accident, N130HP averaged 34-minute missions. The additional takeoffs and the short flights may have consumed more fuel than the contract-based fuel burn rate predicts. Assuming N130HP was loaded to maximum takeoff gross weight at the first flight of the day, the maximum weight at the time of the accident was estimated at 91,553 pounds. Given 13,500 pounds of retardant remaining on board, a contract allowance of 1240 pounds for the flyaway kit, 600 pounds for nominal crew and baggage, and an operating empty weight of 67,928 pounds, the maximum fuel on board at the time of the accident was 8,285 pounds. The maximum zero fuel weight constraint would be violated with the given operating empty weight, crew and crew baggage allowance, flyaway kit allowance, and full retardant load any time additional spares and/or personal effects exceeded 232 pounds. While uncertainties exist with respect to 1) the weight of personal effects, 2) the weight of spare parts compared to the flyaway kit allowance, and 3) the actual fuel burn, N130HP was operated within the maximum takeoff gross weight limits specified in the airplane flight manual, including supplements, according to Safety Board estimates. Airplane Maintenance Records General Maintenance At the time of the accident, T130 had accumulated 21,863 hours time since new (TSN), 45 flight hour since last "A" check, 168 flight hours since last "B" check, and 462 flight hours since last "C" check. The last "A", "B", and "C" checks were all performed by H&P and the inspections were completed on June 17, 2002, September 1, 2001, and March 8, 2001, respectively. The total aircraft flight time at the last "A", "B", and "C" checks were 21,863 hours, 21,695 hours, and 21,401 hours respectively. The last detailed 2,400 hour inspection of the wings was completed as part of a "C" check completed on June 22, 1996, and documented on Work Order (WO) 96-0030. The total aircraft flight time at this "C" check was 20,417 flight hours. H&P's maintenance records for both the left and right outer wings revealed that they were recently installed rehabilitated wings. The Safety Board was unable to find any documentation indicating that SN 56-538 had ever had the center wing replaced. According to H&P's Work Order (WO) 4487, dated May 20, 1998, the left-hand outer wing, SN 3093, was removed and replaced with a rehabilitated outer wing SN 3096L durin
the inflight failure of the right wing due to fatigue cracking in the center wing lower skin and underlying structural members. A factor contributing to the accident was inadequate maintenance procedures to detect fatigue cracking.
Source: NTSB Aviation Accident Database
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