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 valve for each wheel were installed and intact. The fuse plugs from the number 11 and 12 wheels were tested per the Goodrich CMM-32-45-02, Revision 8, by pressurizing them to 225 psi, applying a soap solution, and allowing them to dwell for about 10 minutes. No leakage was noted.

The number 11 inner bead flange had fractured into five fragments comprising the entire circumference. Five (out of nine total) intact rotor drive keys with one still attached to a flange fragment were recovered along with two fractured rotor drive keys. A small piece of one of the fractured rotor drive keys was still attached to a flange fragment. Several segments of the tube well also fractured at the inner bead flange. The rotor drive keys and tube well fragments exhibited radial outward deformation. The number 11 outer bead flange was fractured into seven fragments comprising the entire circumference. There was light abrasion to the outer diameter (OD) of the tube well area on the intact wheel portions that was not present on the mating fragments of tube well. The paint on the inner diameter (ID) and OD of the tube well exhibited no discoloration. There was uniform continuous rubber transfer on both the inner and outer bead flange areas and no evidence of paint peeling or blistering. The tube well area on the number 11 wheel sustained more fragmentation damage than the number 12 wheel tube well area.

The number 12 inner bead flange had fractured into four large fragments that compromised about 90 percent of the circumference of the flange. Portions of heat shield remained attached to three of the fragments. Eight of the nine rotor drive keys remained attached to the inboard flange fragments and all were deformed radially outward. The outboard bead flange fractured into 11 fragments that comprised the entire circumference. There was some smeared rubber on both the inner and outer bead flange areas. There was evidence of two layers of paint on both of the bead seat areas and the upper layer was delaminating or blistering. The paint on the ID and OD of tube well exhibited no discoloration. There was light abrasion to the OD of the tube well areas on the intact wheel portions that was not present on the mating fragments of tube well.

The four inflation valves (part numbers TRJ-781-03) were removed and tested by applying 225 psi to the tire side of the valve. Three of the four valves, numbers 9, 11, and 12, leaked steadily. The number 10 valve did not leak. All four valves were subjected to an X-ray examination in which no obvious damage, deformation, or jamming was noted. The valve core torque was then measured and compared to the design standard of 3 to 5 inch-pounds. The valve cores were then torqued to 4 inch-pounds and air at 50 psi was applied to the tire side of the valve. A soap solution was sprayed on the valve, the pressure was increased to 100 psi, the valves were allowed to dwell for 5 minutes, and then the pressure was dropped back down to 50 psi. Following this pressure test the cores were removed from the valves and examined.

The number 9 valve core required less than 1 inch-ounce of torque to advance. After it was torqued to 4 inch-pounds, some bubbling of the soap solution was noted at 50 psi. The bubbling decreased at 100 psi and continued decreasing during the dwell time. At the return to 50 psi, slight foaming was noted. When the core was removed, debris and corrosion were observed at the seating surface of the barrel seal.

The number 10 valve core required 2.5 inch-pounds of torque to advance. After it was torqued to 4 inch-pounds, no bubbling was observed at any time. When the core was removed, a substantial amount of debris was observed at the seating surface of the barrel seal.

The number 11 valve core required no measurable amount of torque to advance. After being torqued to 4 inch-pounds, some bubbling of the soap solution was noted at 50 psi. The bubbling did not appreciably change during the increase in pressure, dwell, and decrease in pressure. When the core was removed, debris and corrosion were observed at the seating surface of the barrel seal.

The number 12 valve core required less than 1 inch-ounce of torque to advance. After it was torqued to 4 inch-pounds, no bubbling was observed at any time. When the core was removed, corrosion was observed at the seating surface of the barrel seal.

1.6.2 Tires

Per general tire information supplied by Goodyear, overinflation can cause uneven tread wear, reduce traction, make the tread more susceptible to cutting, and increase stress on aircraft tires. The manufacturer indicated that proper inflation of aircraft tires is critical. Underinflation can produce uneven tire wear and greatly increases stress and flex heating in the tire, which shortens tire life and can lead to tire blowouts. The RBLG tires on the accident airplane were to be pressurized to 200 psi per the Boeing maintenance manual instructions. According to maintenance documentation, a tire pressure difference as small as 10 percent could be cause for damage and removal of the tire.

About 30 percent of the number 9 tire, made up of three large pieces and numerous smaller pieces, was recovered and identified. The tire was a new Bridgestone tire that had never been retreaded as evidenced by the absence of a flow stop (the rubber was continuous from the tread area around the shoulder to the bead). The operator reported that the tire had undergone 33 landings since installation. The tire was made up of tread rubber, 2 reinforcing plies, 1 undertread cushion, 2 breaker plies, 16 body plies, and the inner liner. Several pieces exhibited evidence of being cut through some or all of the layers and most of the fragments identified from this tire exhibited a diamond shaped appearance consistent with a burst while pressurized. The footprint, the area of the tire in contact with the ground, was measured to be about 15 inches, consistent with a tire that was not grossly over deflected. Over deflected refers to a tire operated either under inflated for a given load or properly inflated for a given load with additional load added. The identified fragments of tire carcass did not exhibit any evidence of bluing (indicative of the presence of heat), inner liner wrinkling, or melted nylon.

About 50 percent of the number 10 tire, made up five large pieces and numerous smaller pieces, was recovered and identified. The tire was a retread tire that had been retreaded once as evidenced by the presence of R1 on the shoulder. Goodyear manufactured the original casing and Bridgestone-Hong Kong performed the retread. The operator reported that this tire had undergone 175 landings. The tire was made up of tread rubber, 2 reinforcing plies, 1 undertread cushions, 16 body plies, and the inner liner. There was some evidence of FOD damage to the tread but no evidence of cuts through all of the layers on any of the identified pieces. The fragments exhibited a diamond shaped appearance consistent with a burst while pressured. The footprint was measured to be about 15 1/4 inches, consistent with a tire that was not grossly over deflected. The identified fragments of the tire carcass did not exhibit any evidence of inner liner wrinkling. There was some minor evidence of localized bluing and melted nylon.

The number 11 tire was manufactured by Goodyear and had been retreaded once by Goodyear. Based on the retread date and the operator's records, one recovered tire fragment was identified to be from this tire. The operator reported that this tire had undergone 126 landings. This fragment was comprised of four of the body plies with a small area of the sidewall attached. There was evidence of intense heat in the shoulder area with bluing and melted nylon between the sixth and seventh body plies as counted from the exterior, consistent with the tire being operated in an over deflected condition.

The number 12 tire was manufactured by Goodyear and had been retreaded once by Goodyear. Based on the retread date and the operator's records, two large fragments of recovered tread were identified to be from this tire. The operator reported that this tire had undergone 165 landings and the tread wear was consistent with 165 landings. The two pieces comprised about 112 inches of the 154-inch total circumference of the tire. One of the fragments was comprised of the tread rubber, two reinforcing plies, and the undertread cushion and one body ply. The other was comprised of the tread rubber and one reinforcing ply. There was some moderate bluing to the thicker of the two pieces but no evidence of melted nylon.

Many of the tire fragments could not be conclusively identified. These fragments showed varying levels of heat. Some of the fragments exhibited smooth, blue areas with beach marks between the ply layers, indicating a relative motion between the plies that occurred over a period of time.

The four beads from the failed aft tires were examined. All four exhibited gouging and chunking to the bead seat area. All of the damage evidence on the OD of the remaining bead bundles was consistent with the beads rolling on the runway.

1.6.3 Brakes

The number 9 and number 10 brake assemblies were intact with minor damage. The number 11 and number 12 brake assemblies were fragmented into many pieces. No anomalies were noted on any of the brake assemblies or fragments.

1.7 Organization and Management Information

1.7.1 Company Information

Air India began operations in 1971. They operate a fleet of 37 airplanes consisting of Boeing 747-400, Boeing 747-300, Boeing 777-200, and Airbus A310 aircraft. Prior to the accident, they had not experienced any other similar events on their fleet of Boeing 747-400 airplanes. On March 13, 2006, the accident airplane experienced a tire burst of the aft-inboard (number 8) tire located on the left main body gear. During takeoff on April 1, 2006, the accident airplane experienced tire bursts of the aft-outboard (number 7) and aft-inboard (8 tires) located on the left main body gear during takeoff.

1.8 Additional Information

1.8.1 Wreckage Release

The airplane was released to an Air India representative on December 22, 2005. The flight data recorder, cockpit voice recorder, all tire remnants, all wheel assemblies and pieces, and brake discs were retained. The flight data recorder and cockpit voice recorder were released on December 29, 2005. All tire remnants, wheel assemblies and pieces, and brake discs, excluding four tire valves, were released to Air India on February 21, 2006. The tire valves were released to Air India on May 9, 2006. The Safety Board retained no parts or pieces.