Synopsis
On 19 October 2018, a Boeing 747-400F freighter, registered as B-18719 and operated by China Airlines, landed at Singapore Changi Airport at 0443 local time. The aircraft had arrived from Taipei and was scheduled to depart after a transit of about two hours. During a walk-around inspection, the No. 11 tyre (right body landing gear rear inboard) was found to have low pressure. While a technician was inflating the tyre with nitrogen, the tyre burst. The pressure gauge that had been placed on top of the tyre shattered, and debris damaged the aircraft's wing body fairing. Two technicians were involved; one was sent to the hospital for examination and was found to have no injury.
Factual Information
Sequence of Events
The aircraft landed at 0443 LT and taxied to bay 507. It was raining heavily at the time. A Licensed Aircraft Engineer (LAE) and a technician (Technician A) performed a walk-around inspection at about 0500 LT. The LAE suspected low pressure in the No. 11 tyre. After feeling that the tyre was not hot, he instructed Technician A to measure the pressure. The LAE then went to the cockpit and observed that the brake temperature on the EICAS display indicated "0" (on a scale of 0 to 9, where 0 represented a temperature from ambient to 176°C). Technician A measured the tyre pressure at 170 psi using a manual tyre pressure gauge. The LAE, after consulting the Aircraft Maintenance Manual (AMM), decided to apply a Cold Tyre Pressure Check. He determined that the minimum nominal inflation pressure (MinNIP) for the aircraft's take-off weight of 780,000 lb was 185 (+5/-0) psi, and the maximum nominal inflation pressure (MaxNIP) was 213 psi. The LAE calculated a target pressure of 200 psi (the average of MinNIP and MaxNIP) and instructed Technician A to service the tyre to that pressure. Technician B later arrived with a nitrogen servicing cart and measured the same 170 psi. He placed his gauge on the tyre and began inflating. While cycling the charging shut-off valve, he noted the pressure reached 180 psi. He continued inflation, and within seconds, the tyre burst. Technician A felt a blast of cold air to his face and fell to the ground. He was taken to the hospital; no injury was found.
Damage to Aircraft
The manual tyre pressure gauge was completely shattered. The aircraft sustained cracks on the wing body fairing above the tyre, as well as cracks on a composite box structure and a web support structure behind the fairing. A clamp holding an electrical conduit adjacent to the right main landing gear's rear body truck tilt linkage was badly deformed, but the wire within the conduit was undamaged. The No. 11 tyre burst, and subsequent disassembly revealed a continuous circumferential crack under the shoulders of the tyre interior.
Personnel Information
The LAE had 25 years of experience. Technician A had 17 years, and Technician B had 20 years of experience as technicians.
Tyre Servicing Procedures
The AMM defined two tyre pressure check procedures: Cold Tyre Pressure Check (for tyres cooled for at least two hours or not too hot) and Hot Tyre Pressure Check (for tyres too hot to check when time is limited). The Cold Tyre Pressure Check was the preferred method. The tyre service pressure had to be between MinNIP and MaxNIP. For the occurrence aircraft at 780,000 lb, the MinNIP was 185 (+5/-0) psi and MaxNIP was 213 psi. The operator's set tyre service pressure was 200 (+5/-0) psi.
Tests and Research
Examination of the burst tyre showed a continuous circumferential crack along the interior shoulders, consistent with overinflation failure.
Analysis
The investigation assessed that the tyre burst resulted from overinflation with nitrogen beyond its rated burst pressure. The overinflation occurred because the LAE did not follow the AMM procedure for inflation of tyres. Specifically, he incorrectly calculated the target pressure by averaging MinNIP and MaxNIP, and he failed to adhere to the correct tyre pressure check procedure given the elapsed time since landing was less than two hours.