Incident Overview
On April 17, 2016, a Bombardier CL-600-2C10, registration JA06RJ, operated by IBEX Airlines Co., Ltd., was operating as scheduled flight 084 from Fukuoka Airport to Komatsu Airport. Due to adverse weather at the destination, the pilot-in-command decided to return to Fukuoka. During the return flight at an altitude of about 38,500 ft, approximately 33 nautical miles north-northwest of Hiroshima Airport, the aircraft experienced a critical bleed air system failure.
Flight History
At 09:25 Japan Standard Time, while cruising at flight level 400, the left bleed air duct warning (L BLEED DUCT) illuminated on the Engine Indication and Crew Alerting System (EICAS), accompanied by an aural warning. The left bleed air supply stopped due to a detected leak. The flight crew initiated a descent following the Aircraft Operation Manual procedures. At 09:29, shortly after beginning the checklist for the left bleed air leak, the right bleed air duct warning (R BLEED DUCT) activated, and the right bleed air supply also ceased. With both bleed air systems inoperative, the crew declared an emergency and conducted an emergency descent while wearing oxygen masks. While descending through approximately flight level 170, a cabin altitude warning indicated the cabin altitude exceeded 10,000 ft. The pilot-in-command did not deploy passenger oxygen masks, as the cabin altitude rise was gradual. The aircraft continued to descend to about 10,000 ft, and after confirming no further abnormalities, the crew proceeded to Fukuoka Airport, landing at 10:08. No injuries to persons and no damage to the aircraft were reported.
Aircraft and Systems Investigation
The incident aircraft was a Bombardier CL-600-2C10 (serial number 10303), manufactured on May 13, 2010, with a total flight time of 13,614 hours. The bleed air system comprises two independent systems (left and right) that supply high-temperature, high-pressure air from the engine high-pressure compressor to the air conditioning, anti-ice, and other systems. Each duct is equipped with dual-loop sensing elements connected to the Anti-Ice and Leak Detection Controller (AILC), which monitors for bleed air leaks. If both channels detect a leak, the system issues a bleed duct warning and closes the pressure regulating and shutoff valve (PRSOV) to stop air supply.
After the incident, maintenance personnel performed checks on the AILC and sensing elements. The AILC's built-in memory recorded leak detections at specific sensors: MT141 and MT142 on the left system, and MT145 and MT205 on the right system. The Maintenance Diagnostic Computer (MDC) confirmed these records. However, subsequent functional checks and teardown investigations of the AILC revealed no abnormalities. Visual inspection of the four retrieved sensing elements showed oil and fat adhesion on two elements and a slight bend near the connection of another, but nothing that could explain the dual leaks. Ground attempts to reproduce the bleed air leaks were unsuccessful. The AILC had accumulated 11,496 flight hours, and the sensing elements were original to the aircraft.
Past defects on the aircraft included multiple DUCT MON FAULT messages for the left bleed air system, indicating an open loop in one sensing element. The aircraft manufacturer reported that similar past bleed air leak cases were associated with narrow separation between ducts and sensing elements, leading to DUCT MON FAULT messages.
Analysis
Analysis determined that weather and pilot actions were not involved in the incident. The equipment's role remained unknown. Based on recorded data, it is highly probable that the AILC detected bleed air leaks in both systems, causing the stoppage of bleed air supply from both systems. The simultaneous failure of both systems was considered an individual phenomenon for each side.