What happened
On July 7, 2015, a Fuji Dream Airlines flight, operating as scheduled flight 212, was climbing through 32,000 feet toward its destination of Matsumoto Airport. The aircraft, an Embraer ERJ170-200STD with registration JA06FJ, was cruising near 33,000 feet when the left-side bleed air system failed, triggering an EICAS warning. Within 27 seconds, the right-side bleed air system also failed.
This dual failure caused the cabin pressure to drop rapidly, with the cabin altitude eventually reaching 14,550 feet. The crew declared an emergency and initiated an emergency descent. During the descent, the crew noted that the passenger oxygen masks had failed to deploy automatically, requiring the pilot to manually release them. The aircraft diverted to Niigata Airport, landing safely at 15:47 JST. There were 72 people on board, including 67 passengers and 5 crewmembers, and no injuries were reported.
The investigation
The JTSB investigation focused on the mechanical failure of the bleed air systems and the effectiveness of the aircraft's pressure regulation. Investigators examined the fan air valves and the AMS motor drive module removed from the aircraft. Analysis of the valves revealed abrasion and corrosion on the linkages, as well as the presence of fine particles—composed of silicon, aluminum, and elements similar to volcanic ash—on the internal air filters.
Further investigation into the airline's maintenance records showed that the aircraft was equipped with older-style air filters. While a Service Bulletin had been issued to upgrade to higher-capacity filters, the implementation was not mandatory, and the airline had only planned to replace them during scheduled valve maintenance. Additionally, the investigation found that the airline had previously experienced similar, albeit brief, simultaneous bleed air interruptions on other aircraft in its fleet.
Findings
The investigation established that the abnormal depressurization was caused by the simultaneous cessation of bleed air supply from both engines. This occurred because the fan air valves malfunctioned, preventing sufficient airflow for cooling the bleed air. As the temperature of the air exceeded safety thresholds, the engine's pressure regulating shut-off valves (NAPRSOV) automatically closed to protect the system.
Several contributing factors were identified:
- Mechanical degradation of the valves due to corrosion and abrasion on the linkages.
- Inadequate filtration of air entering the valve actuators, as the aircraft was using older-type air filters that allowed volcanic ash particles and other debris to enter the mechanism.
- Potential heat-induced deterioration of the torque motors within the valves.
- A lack of sufficient reliability management within the airline's maintenance system, which failed to recognize the escalating risk posed by recurring, short-duration dual-system anomalies.