What happened
On 13 November 2008, during a pre-departure inspection at Manchester Airport, a crew member identified a small cut in the tread of a main-wheel tyre on a Bombardier CL600-2B19 CRJ200, registration D-ACHA. Following instructions from the company's engineering centre in Cologne, a technician travelled to the airport to perform a wheel change and a scheduled five-day maintenance check.
While the technician was working on the aircraft, he attempted to replenish the pressure of a spare tyre using a nitrogen pressure rig. During the process, the technician briefly pressed the inflator lever. The wheel assembly subsequently exploded, causing the technician to sustain serious injuries. The force of the explosion was significant enough that another employee, working inside the aircraft cabin, felt the aircraft move and heard the sound of escaping gas.
The investigation
Investigators examined the wreckage of the nosewheel and the nitrogen pressure rig. The investigation established that the wheel, which consisted of two forged halves joined by eight tie bolts, suffered a catastrophic failure. Metallurgical analysis showed that seven of the eight tie bolts had undergone staged tensile rupture.
Regarding the inflation equipment, the investigation found that the pressure rig was a non-standard unit with several complicating factors. The regulator valve on the rig was capable of delivering gas at pressures up to 1,500 psi, yet the delivery gauge was annotated in bars rather than psi. This discrepancy, combined with the technician's unfamiliarity with this specific rig, likely contributed to the error. Furthermore, the technician did not check the regulator's pressure gauges before connecting the adapter to the tyre valve.
Findings
- The primary cause of the explosion was extreme over-inflation, with the tyre pressure reaching approximately six times the normal operating level.
- The technician likely failed to realize the regulator was set to a high-pressure state because the delivery gauge used bars, making the numerical value appear much lower than the actual pressure in psi.
- The small size of the nosewheel tyre meant that the pressure rose much more rapidly than it would have on a larger aircraft tyre, leaving the technician no time to react to the rapid increase.
- The wheel lacked an overpressure burst protection valve, an optional feature that was not installed on this specific aircraft model.