What happened
On October 30, 2019, an IBEX Airlines Bombardier CL-600-2C10, registered JA11RJ, was operating a scheduled flight from Sendai to Fukuoka. While cruising at 34,000 feet, the pilot observed flashes near the left cockpit window, accompanied by 'L WSHLD HEAT' caution messages on the EICAS. Following the established checklist, the pilot attempted to reset the windshield heat settings.
Shortly after, the pilot observed what appeared to be cracks in the left windshield. In accordance with the emergency procedures for windshield damage, the pilot transitioned the cabin pressurization to manual mode and set the cabin altitude to climb at the maximum rate. This procedure caused the cabin altitude to rise rapidly. As the aircraft began an emergency descent to 10,000 feet, the cabin altitude exceeded 14,000 feet, triggering the automatic deployment of passenger oxygen masks. The aircraft eventually landed safely at Fukuoka Airport.
The investigation
The JTSB investigation focused on the electrical phenomena observed in the cockpit and the subsequent pressurization changes. Investigators examined the removed left windshield and side window, finding that while no structural cracks were present in the glass, there were arcing marks on the upper part of the left windshield heater element. The investigation also reviewed maintenance records, noting a recent repair to the moisture seal on that same window.
Technical analysis of the aircraft's flight data revealed that the cabin altitude exceeded 10,000 feet for over ten minutes. The investigation also reviewed the manufacturer's checklist, which mandates a specific manual pressurization setting for windshield damage regardless of the current flight altitude.
Findings
- The flashes seen by the crew were caused by arcing within the left windshield heater element.
- The arcing was likely caused by moisture penetrating the windshield due to the deterioration of the moisture seal.
- The pilot followed the prescribed emergency checklist for windshield damage, which requires increasing the cabin altitude rate.
- The rapid increase in cabin altitude, necessitated by the checklist, led to the abnormal decompression and the deployment of oxygen masks.