What happened
On July 1, 2010, a Bombardier CRJ700, registration F-GRZF, operated by Brit Air, was performing a scheduled passenger flight when an incident occurred during the landing roll at Paris Roissy Charles de Gaulle. The flight crew reported hearing a loud detonation accompanied by the smell of smoke. Simultaneously, the Engine Indicating and Crew Alerting System (EICAS) indicated a loss of oxygen pressure for the flight crew system.
Following the landing, the crew requested fire services to perform an external inspection of the aircraft. Upon reaching the parking stand, maintenance technicians discovered that the pressure sensor for the flight crew oxygen circuit had been destroyed and showed visible burn marks. \n## The investigation
The investigation focused on the mechanics of the oxygen system and the physical state of the failed sensor. The aircraft's oxygen system consists of two independent parts: a gaseous oxygen cylinder for the flight crew and a chemically generated oxygen system for passengers and cabin crew. The flight crew's system utilizes a cylinder containing approximately 1,415 liters of oxygen at 1,850 psi.
Investigators examined the pressure sensor (P/N CMC 1904), which had been previously installed as part of a fleet-wide replacement program. The examination revealed that the sensor body had ruptured at the electrical input/output connector. Testing the damaged unit at a pressure of 870 psi revealed a micro-leak of approximately 2 ml per hour between the high-pressure oxygen inlet and the electronic compartment. Further analysis of the measuring cell showed cracks in the welding and the material of the cell body.
Additionally, the electronic motherboard showed significant damage. The voltage regulator component was missing, and black residue was found around its location. As this is a power component, its failure likely caused a localized temperature increase.
Findings
- The sensor likely contained production defects in the welding or material that went undetected during installation.
- These defects led to the formation of micro-fissures, resulting in a continuous micro-leak of oxygen into the electronic compartment.
- The accumulation of oxygen under pressure within the electronic housing created an oxygen-enriched environment.
- The auto-ignition of a voltage regulator component within this high-pressure, oxygen-rich environment caused the explosion.