What happened
On April 18, 2022, an IBEX Airlines flight operating a Bombardier CL-60/2C10, registration JA07RJ, was en route from Sendai Airport to Fukuoka Airport when the crew encountered significant instrument malfunctions. While cruising at FL 360 over Oda City, Shimane Prefecture, the Engine Indicating and Crew Alerting System (EICAS) triggered "STALL FAIL" and "RUD LIMIT FAULT" messages.
Simultaneously, the pilot in charge (PIC) and the first officer (FO) observed the indicated airspeed (IAS) on both primary flight displays steadily decreasing from 258 knots toward a minimum of 40 knots, despite no change in the aircraft's actual speed. To prevent unintended maneuvers, the PIC disengaged the autopilot and flight director. The crew relied on the Integrated Standby Instrument (ISI), which continued to show stable and normal airspeed. After the airspeed indications on the primary displays recovered to normal levels at approximately FL 240, the crew continued the descent and landed safely at Fukuoka Airport.
The investigation
The JTSB investigation examined the aircraft's pitot-static system, including the heating elements, drain holes, and collector tubes. Post-incident inspections, including X-ray CT scans of the pitot-static probes, revealed no mechanical obstructions, leaks, or heater failures. The investigation also reviewed meteorological data, noting that the aircraft had flown through an area near the tropopause where air convection can suspend ice crystals. The investigators analyzed flight data recorder (FDR) records, which showed the airspeed values on both primary displays dropped and recovered almost simultaneously.
Findings
- The investigation determined that the ice crystal blockage of the pitot system was the most likely cause of the erroneous airspeed readings.
- It is probable that the aircraft flew through an airspace containing ice crystals, which accumulated on the downstream side of the drain hole.
- The blockage likely occurred because the crystals were at a temperature that prevented immediate melting by the probe heaters.
- The recovery of the airspeed indications was likely caused by the aircraft descending into warmer air, which melted the accumulated crystals.
- The standby pitot-static system remained functional because its probes and ports are located in different positions and have different internal structures than the primary system.