Los Angeles, CA, USA
VT-AIM
Boeing 747-400
The four right main body landing gear tires burst during the takeoff ground roll, and the crew performed a precautionary landing. Pieces of the tires and wheel assemblies penetrated the fuselage structure and the airplane incurred substantial damage. Post accident examination revealed that the valve cores on three of the four inflation valves, including the two aft valves, were not torqued to the manufacturer's specifications and leaked steadily. Examination of the right aft main body landing gear tires (number 11 and 12) showed that they were operated in an over deflected condition at some point prior to the event, which resulted in internal damage to the tires. The aft tires failed first as a result of the internal damage and initiated the accident sequence. Damage to the forward tires was consistent with the tires bursting due to their impact by debris from the aft tires.
1.1 History of Flight On December 19, 2005, at 2030 Pacific standard time, the four right body landing gear (RBLG) tires on a Boeing 747-400, Indian registry VT-AIM, operating as Air India 136, burst during takeoff from Los Angeles International Airport, Los Angeles, California. Air India was operating the airplane under the provisions of 14 CFR Part 129. The captain, first officer, a relief captain, 14 flight attendants, and 256 passengers were not injured; the airplane sustained substantial damage. The scheduled international passenger flight was originating at the time and was destined for Frankfurt International Airport, Frankfurt, Germany. Visual meteorological conditions prevailed and an instrument flight plan was in effect. Following the airplane's liftoff from runway 25R, a member of the Los Angeles airport operations was notified that there appeared to be foreign object debris (FOD) on the runway. The airport operations specialist was positioned near the end of runway 25R, on the taxiway, and had heard two loud, succinct booms as the airplane rotated from the runway. The specialist proceeded down runway 25R and noted a substantial amount of debris on the runway and adjoining taxiways. The majority of the debris was located about 2,500 feet to 10,000 feet from the east end of the 12,091-foot runway. The first identified debris field contained two sections of rubber and was located about 2,500 feet from the east end of the runway. About 4,000 feet from the east end of the runway were metal pieces identified as landing gear wheel fragments. The majority of the debris continued down the runway to about the 10,000-foot point, and contained large sections of the wheels and rubber portions of the tires. After the event, the airplane circled off shore to jettison fuel in order to land. The specialist that reported and identified the initial debris on runway 25R reported that after the airplane landed there was some debris on runway 25L. As the airplane approached the east end of runway 25L to land, the specialist noted that none of the main body landing gear tires on the right side were evident. The airplane touched down at 2155. Examination of the runway 25R surface revealed no marks along the right side of the runway centerline prior to the 2,500-foot point. Rubber tire marks were noted in a feather-like, brush pattern approximately 3,000 feet from the east end of the runway, and again approximately 10,000 feet from the east end of the runway. Groove marks along the runway centerline and to the right of the centerline were present intermittently on the surface about mid-runway length. Following the landing, emergency crews responded and sprayed water on the airplane's brake system to keep them cool. The passengers were deplaned using the stairs while the airplane was on the runway. Airport operations personnel closed both runway 25L and 25R overnight to facilitate the clean up of the runways. The captain, the flying pilot for this leg of the flight, reported that the time leading up to the takeoff was uneventful. They taxied the airplane for 15 to 20 minutes. As he rotated the airplane for takeoff, he felt a slight vibration. He continued the takeoff, which he identified as normal, but felt a shudder. At 400 feet above ground level (agl), the engine indication and crew alerting system (EICAS) displayed warning messages to the flight crew. Shortly thereafter, a tower controller informed the crew that there was debris on the runway. After receiving a series of messages from EICAS, the captain climbed the airplane to 15,000 feet and attempted to retract the flaps. The flaps remained extended 10 to 20 degrees. As the airplane was climbing, an air traffic controller advised the captain that there were metal hinges and brake parts on the runway. The captain jettisoned the fuel and returned to land. While on an extended final for runway 25L, he extended the flaps to 25 degrees, however, the landing gear warning horn went off and the flaps automatically retracted to 20 degrees. During the touchdown, the thrust reversers came to the interlock position; however, engines 2 and 3 did not go past interlock. The airplane was brought to a stop using manual braking. The rescue crews confirmed that there was no fire and the passengers were deplaned. Prior to the flight, the first officer (FO) performed a walk-around of the airplane. No mechanical problems or abnormalities were identified by the FO or reported to the captain. A maintenance engineer also examined the airplane prior to its departure with no problems noted. Information regarding the takeoff portion of the flight was obtained from the flight data recorder (FDR). Approximately 39 seconds after the airplane began its takeoff roll, the lateral acceleration increased from approximately 0 g to 0.153 g down to -0.161 g and the airplane traveled approximately 3,000 feet. About 18 seconds later, the vertical acceleration peaked at 1.96 g, the lateral acceleration peaked at -1.083 g, and the airplane traveled approximately 7,290 feet. Less than 1 second later, the air-to-ground discrete transitioned from "Ground" to "Air". Twelve seconds later, the gear disagree discrete transitioned from "Normal" to "Disagree." 1.2 Damage to Aircraft The airplane was examined on the United Airlines maintenance ramp at Los Angeles International Airport on December 21, 2005. National Transportation Safety Board investigators, personnel from the Federal Aviation Administration (FAA), and Air India were present. The forward end of the RBLG wheel well is the station (STA) 1350 bulkhead, and the aft end of the wheel well is the STA 1480 bulkhead. The third vertical stiffener from the inboard end of the wheel well on the STA 1350 bulkhead exhibited impact damage and a cracked upper cap. A hydraulic return line located between the brake control valve and the anti skid valve was pierced by the cracked vertical stiffener. There was deformation to a flight control hydraulic pressure line that ran along the STA 1350 bulkhead and a clamp had torn away where it attached to a stiffener. The electrical control unit on top of the flap control valve exhibited impact damage. There was a small puncture (1 inch by 1/2 inch) in the upper pressure deck, and a light assembly attached to the pressure deck had a piece of rubber embedded in it. There were several areas of black rubber transfer on the wheel well structure, and numerous small pieces of rubber debris were found in the wheel well. No evidence of any metal rim debris was found in the wheel well. Towards the aft end of the wheel well was a damaged hydraulic pressure line situated between the brake control valve and RBLG, and a damaged pressure line that runs from the brake accumulator through the STA 1480 bulkhead. There was no damage evident to any of the flight control cables or flap torque tubes that run through the wheel well. There was puncture damage and many areas of black rubber transfer to the exterior of the forward body landing gear door that normally stays closed unless the landing gear is in transit. There was puncture damage through both the interior and exterior surfaces of the main body landing gear door that is slaved to the RBLG, and the link that attaches the door to the gear was broken at each end where the tie rods attach. The downlock bungee failed at its attach point to the downlock link. The exterior of the main wing landing gear door exhibited black rubber transfer and puncture damage. The wing-to-body fairing exhibited several areas of puncture damage between STA 1480 and the end of the fairing at STA 1680. There were pieces of the wheel assemblies and brake fragments found within the fairing. The wing-to-body fairing frames at STA 1540, 1580, and 1620 exhibited impact damage. The 1540 frame had a small puncture in the web and cracked upper cap. The 1580 frame was missing a large piece of the web and lower cap while the upper cap was present but deformed. The 1620 frame had a hole in the web and a cracked upper cap. The fuselage skin underneath the wing-to-body fairing had several punctures adjacent to the fairing damage and several large pieces of the fragmented wheels were found embedded in the skin. The damage to the fuselage under the wing-to-body fairing was located in the area between two lap joints on the lower right side of the fuselage. Between STA 1520 and 1560, there were three relatively large holes, which measured 10 inches by 8 inches, 10 inches by 10 inches, and 8 inches by 4 inches, respectively, along with several smaller holes and scraping damage. There were three additional holes between STA 1600 and 1640 that measured 3 inches by 3 inches, 8 inches by 2 inches, and 10 inches by 16 inches, along with several more areas with dents and scraping damage. The lower fuselage skin aft of the wing-to-body fairing between STA 1680 and 1720 sustained two small punctures, which measured 1 inch by 1/2 inch and 2 inches by 2 inches, respectively. The lap joint on the aft cargo door sustained impact damage that peeled a small section of skin upwards. There was some scraping, and paint and rubber transfer associated with this damage. The leading edge of the right horizontal stabilizer had some rubber transfer and impact damage, and the right inboard elevator sustained puncture damage. Examination of the wheel fragments revealed that the bead flanges fractured at the transition area to the hub. The failed outer flange pieces from both wheels were smaller than the inner flange pieces. A majority of the fragments from all four flanges were recovered and reconstructed on the tarmac. There was significant abrasion damage on the outer most circumferences of all the bead flanges. The outer hub circumferences also exhibited the same abrasion damage. The intact wheel assemblies that remained on the forward axle also exhibited the same abrasion damage, although lighter in appearance. 1.3 Other Damage Following the accident, airport personnel performed inspections of runways 25L and 25R at Los Angeles International Airport. Airport personnel noted that seven runway centerline lights were damaged on runway 25R between taxiways J and M. In addition, two runway centerline lights and one taxiway leadline light were damaged on runway 25L just west of taxiway G. The runway concrete damage was limited to skid marks, scrape marks, and grooving on the concrete. 1.4 Aircraft Information 1.4.1 General Aircraft History The airplane was manufactured in 1991 and delivered to Air Canada. Air Canada operated the airplane for 13 years from 1991 to 2004. A leasing company acquired the airplane in September 2004, and placed it into storage. In April 2005, Air India leased the airplane for a period of 3 years. The airplane was based in Delhi, and operated on the Delhi to Frankfurt to Los Angeles route three times per week. At the time of the accident, the airplane had accumulated 54,356 hours and 8,376 cycles. Air India representatives reported that an onboard indication of tire pressure was available on the airplane as standard equipment; however, it had been deactivated for commonality purposes with other Air India airplanes. Real time brake temperatures were displayed to the crew. 1.4.2 Weight and Balance A load sheet was obtained from Pacific Aviation, the Los Angeles-based coordinator for Air India. The takeoff weight was 845,649 pounds (383,580 kilograms) and the total fuel weight was 316,363 pounds (143,500 kilograms). The maximum takeoff weight for the airplane was listed as 869,999 pounds (394,625 kilograms) on the load sheet. 1.4.3 Maintenance Information The last maintenance performed on the airplane was a 2A Check completed on December 2, 2005, at an Air India maintenance base in Mumbai. On October 6, 2005, a 4A check was completed in Mumbai. The last major maintenance check was completed on April 15, 2005. The D2 check was completed at the Malaysian Airlines facility at Subang, Kuala Lumpur, Malaysia, prior to the airplane attaining its Indian registration number on April 28, 2005. The last tire servicing was in Delhi on December 18. The main wheel tire pressures were 200 pounds per square inch (psi) and the nose wheel pressure was 185 psi after servicing. Maintenance personnel recorded the tire pressures after the tires were serviced in Delhi. Tire pressures prior to servicing were not recorded. Transit checks were completed in Frankfurt and Los Angeles. No tire pressures were recorded during the transit checks. Placards affixed to the main body landing gear struts on the accident airplane showed that the main body gear tires should be inflated to 190-195 psi. It was confirmed that these placard values were incorrect for the certified gross weight of this airplane. Air India confirmed that they inflate the tires to 200 psi instead of the values stated on the placards. 1.5 Flight Recorders The airplane was equipped with an L-3 Communications Fairchild Flight Data Recorder in addition to a Honeywell 6022 SS Cockpit Voice Recorder (CVR) 120. A Collins Central Maintenance Computer (CMC) monitored the airplane systems. 1.6 Tests and Research The two intact forward wheel and brake assemblies, the two damaged aft wheel and brake assemblies, and all of the debris collected from the runways, were shipped to the Boeing Equipment Quality Analysis (EQA) Laboratory in Seattle, Washington, and examined by the Safety Baord Structures Group Chairman and members of the structures group. The complete Structures Group Factual Report is contained in the official docket of this investigation. 1.6.1 Wheels The wheels on the RBLG are numbered as follows: 9 forward-inboard; 10 forward-outboard; 11 aft-inboard; and 12 aft-outboard. The RBLG wheels are manufactured in two halves, inner and outer, that are mated together with tie bolts through the center hub area. The outer bead flange is adjacent to the wheel split line on the outer wheel half while there is an extended tube well between the inner bead flange and wheel split line on the inner wheel half. The brake assembly is housed within the inner wheel half and is separated from the wheel by a heat shield. The brake rotor drive keys attach to the wheel flange (chin) with bolts, and the pin end engages holes in the inboard wheel half near the tie bolts. There are three fuse plugs and an over inflation plug installed in each wheel assembly. The fuse plugs have a core that is designed to melt at a specified temperature to relieve tire pressure in the event of an overheat condition. The over inflation plug is designed to release tire pressure in the case of over inflation. There is a bearing installed in the center diameter of each wheel half The number 9 and 10 wheel assemblies exhibited similar damage patterns. The inner tire bead was seated on the number 9 wheel while all of the others were free to rotate around the hubs. There was light abrasion damage to the outer circumference of the bead flanges on both wheels. All of the bearings were free to rotate with grease present. The heat shields and rotor drive keys remained installed although the number 10 heat shield exhibited some minor deformation. The number 11 and 12 wheel assemblies fractured in the same general manner. The bead flanges fractured from the wheel halves about 2 inches from the split line on both the inner and outer halves at the transition area between the center hub and tube well. The failed outer bead flange pieces from both wheels were smaller than the inner flange pieces. A majority of the fragments from the four flanges were recovered and reconstructed. All of the fracture surfaces were examined and exhibited a dull, grainy appearance consistent with overload. None of the wheel fragments exhibited visible signs of corrosion. There was significant abrasion damage on the outer most circumferences of the bead flanges, and the outer hub circumferences exhibited the same abrasion damage. All of the bearings were free to rotate with grease present. The wheel halves remained mated together with all of the tie bolts installed for both wheels. The three fuse plugs and one overinflation
the incorrect installation of the inflation valve cores in the number 11 and number 12 wheel assemblies that allowed the tires to be operated in an over deflected condition that resulted in their failure.
Source: NTSB Aviation Accident Database
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