What happened
On December 4, 2017, at approximately 19:23 UTC, an Embraer 170-100 departed from Warsaw Chopin Airport (EPWA) for a scheduled flight to Paris (LFPG). The aircraft was permitted to fly under the Minimum Equipment List (MEL) due to an existing inoperative second bleed system.
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 flight crew requested air traffic control to level off at FL140 and performed the necessary checklists in accordance with the Quick Reference Handbook (QRH). Following consultation with Maintenance Control Center (MCC) via radio, the decision was made to return to Warsaw due to the failure of the first Nacelle Pressure-Regulating Shutoff-Valve (NAPRSOV) in conjunction with the already inoperative second valve.
The aircraft landed safely at EPWA without further incident.
The investigation
The investigation focused on the malfunction of the engine bleed air system valves. It was established that the failure of the first valve was caused by engine-induced vibrations, which led to erratic valve behavior, specifically momentary opening and closing. The investigation also noted that the operator's technical department analyzed the failure, observing that the malfunction had recurred several times prior to the replacement of the NAPRSOV valve.
Findings
- The primary cause of the incident was a defective valve design that caused pressure fluctuations.
- Engine vibrations contributed to the irregular operation of the valve.
- The manufacturer was aware of the issue, with a service bulletin regarding a modification to the NAPRSOV valves (incorporating additional damping mass and an insulator to improve durability) scheduled for release in the final quarter of 2018.