What happened
On December 4, 2017, at approximately 19:23 UTC, an Embraer 170-100 departed from Warsaw Chopin Airport (EPWA) bound for Paris (LFPG). The aircraft was operating under a Minimum Equipment List (MEL) authorization for an inoperative bleed air system (BLEED 2 INOP).
During the initial climb, after passing through an icing layer at approximately FL100, the crew received a BLEED 1 LEAKAGE caution followed by an A-I WING FAIL indication. The crew requested air traffic control to level off at FL140 and performed the necessary checklists according to the Quick Reference Handbook (QRH). After consulting with Maintenance Control Center (MCC) via radio, the decision was made to return to Warsaw due to the simultaneous failure of both bleed air valves. The aircraft landed safely at EPWA without further incident.
The investigation
The investigation focused on the malfunction of the Nacelle Pressure-Regulating Shutoff-Valves (NAPRSOV). It was established that the failure of the number 1 valve was caused by engine-induced vibrations, which led to erratic valve behavior, including momentary opening and closing. The investigation noted that the operator's technical department analyzed the failure, observing that the number 1 valve had malfunctioned several times prior to February 2018, eventually resolving after the valve was replaced.
Findings
- The primary cause of the incident was a defective valve design that caused pressure fluctuations.
- Engine vibrations caused the NAPRSOV to operate atypically.
- The manufacturer was aware of the valve issue, with a service bulletin for a modification (adding a vibration-damping mass and insulator to improve valve longevity) scheduled for the final quarter of 2018.