What happened
On 15 November 2003, an Embraer EMB-145EP, registration G-EMBD, was preparing for a scheduled passenger flight from Venice, Italy, to Manchester, UK. During the takeoff ground roll at Venice Airport, the aircraft reached rotation speed when the flight crew experienced a sudden, moderate vibration. Because cockpit systems indicated no other malfunctions, the commander elected to continue the takeoff.
Following the departure, Venice air traffic control conducted a runway inspection, which uncovered tyre debris on the departure runway. The flight proceeded to Manchester, where the crew declared an emergency upon approach. The aircraft landed safely on Runway 24L without further incident. Subsequent maintenance inspections revealed that the left inboard mainwheel tyre had lost its tread and deflated, and the flying debris had severed wiring for the weight-on-wheels switch on the landing gear.
The investigation
Investigators examined the failed tyre and its companion wheel. The failed tyre, which was on its second retread, showed evidence of overheating and significant internal damage. The examination determined that the tread had separated from the carcass due to the failure of the internal casing plies. This failure was caused by overstress in the tyre sidewall, which occurred because the tyre had been operating under-inflated.
Further inspection of the wheel assembly identified an extensive air leak originating from the overpressure valve. Metallurgical analysis of the valve seat revealed a cavity caused by penetrative corrosion. This corrosion was linked to a thin or missing anodising layer on the valve seat, likely due to a manufacturing flaw in the manual cleaning process used prior to 2001. Additionally, the O-ring seal on the valve had degraded, potentially due to the use of Molycote 111, a lubricant known to be incompatible with silicone rubber.
Findings
- The tyre tread separation was caused by excessive sidewall deflection resulting from under-inflation.
- The loss of pressure was driven by an air leak from the overpressure valve caused by corrosion on the valve seat.
- The corrosion was facilitated by a lack of adequate protective anodising in the valve seat area during manufacture.
- The degradation of the O-ring seal was likely accelerated by the application of an incompatible lubricant.
- Maintenance procedures and ambiguities in the Component Maintenance Manual (CMM) meant the valve seat was not inspected during routine tyre changes.