NTSB Factual Report

HISTORY OF FLIGHT

On June 29, 2007, about 0155 Pacific daylight time, Air China flight 984, a Boeing 747-400, B-2470, experienced burst tires and accompanying wheel disintegration during takeoff from Los Angeles International Airport (LAX), Los Angeles, California. Air China was operating the airplane as a scheduled international passenger/cargo flight under the provisions of 14 Code of Federal Regulations (CFR) Part 129. The captain, first officer, 2 backup crew, 10 flight attendants, and 223 passengers were not injured; the airplane sustained minor damage. Visual meteorological conditions prevailed, and an instrument flight rules (IFR) flight plan had been filed. The flight was departing as a non-stop to Beijing, China.

According to the flight crew, during the takeoff roll from runway 25R at LAX, the two aft tires, numbers (No.) 11 (inboard) and 12 (outboard), on the right body landing gear (RBLG) burst and the two aft wheels fractured, which caused minor damage to the airplane. Prior to returning to LAX, the captain dumped fuel in order to reduce the landing weight. The airplane landed uneventfully on runway 25L.

WRECKAGE AND IMPACT INFORMATION

The 25R and 25L runways were closed while airport operations personnel collected the foreign object debris (FOD). Maintenance technicians replaced the No. 11 and 12 wheels and moved the airplane to the ramp area for further examination. Technicians deflated the No. 9 and No. 10 tires due to the damage that they sustained. Airport operations personnel reported that the first debris on the takeoff runway consisted of rubber tire fragments, followed by metal and carbon brake fragments, and then metal wheel debris.

National Transportation Safety Board investigators and the FAA examined the airplane on June 29 and 30, 2007, at LAX. The examination revealed numerous punctures, scraping damage, and areas of black rubber transfer on the forward RBLG door, the inboard RBLG door, and the inboard right wing landing gear (RWLG) door. Some of the wire bundles on the RBLG were damaged and/or severed, and the four brake hydraulic lines were severed near the outboard trunnion. Scraping and mechanical damage were noted on the strut, drag brace, and various brackets on the RBLG. Minor damage was observed in the RBLG wheel well area. The No. 9 tire exhibited several cuts, and the No. 10 tire exhibited several cuts and had one large chunk missing. The wing-to-body fairing exhibited several areas of puncture damage, and black rubber transfer marks were located between STA 1480 and the end of the fairing at STA 1680. Fragmented sections of the wheel assemblies and brake fragments were embedded in the fairing. The fuselage aft of the wing-to-body fairing sustained one small punctured hole and several areas of denting and/or scraping/gouging damage.

Fragments from the aft wheel assemblies (S/N A1868 and 3829) were recovered from the runways. Three of the four bead flanges fractured at the transition area to the hub. The inboard bead flange on one wheel assembly was intact for about 75 percent of the circumference. The failed outboard flange pieces from both wheels were smaller than the inboard flange pieces. A majority of the fragments from the three failed flanges were recovered and reconstructed on the tarmac. A Safety Board structural engineer examined all of the fracture surfaces, and noted overload signatures. There was significant abrasion damage on the outer most circumferences of all the bead flanges.

Examination of runway 25R revealed gouging consistent with the dimensions between the wheel flanges beginning at about the taxiway WF intersection. The gouging was present, although not continuous, until about 200 feet beyond the taxiway M intersection. The gouging was at or to the left of the runway centerline. Investigators were not able to examine the landing runway (25L) since it was in use at the time of the examination.

Tire pressures were measured in all remaining tires on the airplane, and the pressures ranged between 179 and 205 pounds per square inch (psi). In addition, the airplane was equipped with a tire pressure indicating system. The data review results from the engine indicating and crew alerting system (EICAS) agreed with the measured pressures.

The No. 11 and 12 tires, wheels, and brake assemblies were retained for further examination.

FLIGHT RECORDERS

The airplane was equipped with a Honeywell Solid State Flight Data Recorder (FDR), model number 980-4700-003, serial number 3972, which recorded airplane flight information in a digital format using solid-state flash memory as the recording medium. The FDR recording contained approximately 53.8 hours of data.

TESTS AND RESEARCH

Engine Indicating and Crew Alerting System (EICAS)

The Boeing 747-400 airplane was equipped with an EICAS computer in the cockpit. The fault summary report for the incident flight was captured and reviewed. The first fault noted on the report occurred at 0144, and was listed as "ABNORMAL TIRE PRESSURE CONDITION". At 0144:50, the EICAS system recorded a tire pressure on the right aft wheel of the RBLG, tire No. 12, of 144 psi. All other main landing gear tire pressures were between 204 and 231 psi. Beginning at 0153, numerous faults with the brake system, hydraulic system, and RBLG were recorded and stored in the computer.

Examination of the FDR data revealed at the time of the 0144 EICAS message, the airplane's position at LAX was just prior to a turn onto taxiway B, which was a parallel taxiway to runway 25R.

Tire Pressure and Tire Pressure Indication System (TPIS)

The airplane was equipped with a TPIS that continually monitored the tire pressure and supplied fault signals to the EICAS computer. For the month preceding the incident, the recorded tire pressures for the main landing gear wheels varied between 194 and 234 psi. Prior to departure on the day of the incident, the tire pressures were checked by maintenance personnel and no anomalies were noted. The tire pressures were provided to the flight crew with the flight dispatch paperwork.

Weight and Balance

Air China provided the weight and balance data for the airplane for the incident flight, and for the month of June 2007. On the incident flight, the takeoff weight was 811,430 pounds. For the month of June, the takeoff weights ranged from about 518,000 and 847,000 pounds. The maximum takeoff weight for the airplane was 850,000 pounds.

Wheels

On July 23 and 24, 2007, at the facilities of Boeing Equipment Quality Analysis Laboratory, Everett, Washington, under the supervision of a Safety Board structures engineer, the tires, wheel and brake assemblies, and associated debris were examined.

The No. 11 wheel assembly inboard bead flange was fractured from the wheel and recovered in 4 sections, which comprised 85 percent of the circumference. The outboard bead flange was partially intact, which comprised 75 percent of the wheel. All fracture surfaces exhibited a dull, rough appearance consistent with overload. No visible evidence of corrosion was observed on any of the wheel fragments. The tire pressure indication system (TPIS) components remained installed.

The No. 12 wheel assembly inboard bead flange was fractured from the wheel and recovered in 4 sections, which comprised the entire flange circumference. The outboard bead flange was fractured from the wheel and recovered in 7 sections, which comprised 80 percent of the wheel. All fracture surfaces exhibited a dull, rough appearance consistent with overload. No visible evidence of corrosion was observed on any of the wheel fragments. The tire pressure indication system (TPIS) components remained installed.

The 6 fuse plugs, 2 inflation valves, and 2 over pressure valves were removed and tested by applying 180 psi and a soap solution. The No. 11 over pressure valve exhibited signs of leakage. Examination of that valve revealed a slightly higher leakage rate (4 psi versus 2 psi) over a 24-hour period as compared to a new valve. A detailed examination of the valve was unable to determine the reason for the higher leakage.

Tires

The No. 11 tire was originally manufactured by Goodyear-Thailand and had been recently retreaded by Goodyear-Thailand. Sixteen tire fragments and two bead bundles were identified to be from the No. 11 tire, which comprised 30 percent of the tire. The fragments exhibited evidence of intense heat damage in the lower sidewall area with bluing and melted nylon. Many of the fragments failed in a diamond-shaped pattern consistent with a burst under pressure. The centerline tread depth on the fragments measured between 2/32 and 4/32 inches.

The No. 12 tire was originally manufactured by Goodyear-Thailand and had never been retreaded. Eighteen tire fragments and two bead bundles were identified to be from the No. 12 tire, which comprised 25 percent of the tire. Two mating sections exhibited evidence of a cut through all the plies and the inner liner about 1-inch wide. The failure pattern of the two mating sections did not indicate a tire burst due to a cut. The other fragments exhibited evidence of intense heat damage in the shoulder area with bluing and melted nylon. Many of the fragments failed in a diamond-shaped pattern consistent with a burst under pressure. The centerline tread depth on the fragments measured between 5/32 and 6/32 inches.

Brakes

The No. 11 brake assembly rotors were missing. The torque takeout clevis was abraded to about 3/4 inches from the lower edge of the bushing and there was deformation to the piston housing heat shield. Both axle bushings appeared normal with grease present in the grooves. The stack height was about 4 3/4 inches.

The No. 12 brake assembly rotors were missing. The torque takeout clevis was abraded to about 9/16 inches from the lower edge of the bushing and there was deformation to the piston housing heat shield. Both axle bushings appeared normal with grease present in the grooves. The stack height was about 5 3/8 inches.

NTSB Probable Cause

The loss of pressure in the number 12 tire due to inadvertent contact with foreign object debris while taxiing prior to takeoff, which resulted the number 11 tire to over deflect and burst during takeoff roll. Contributing to the incident was the failure of the flight crew to detect and act upon the EICAS message alerting them to the loss of pressure in the number 12 tire.