What happened
On January 16, 2019, a Bombardier/DHC8-402, registration SP-EQE, was climbing through approximately FL200 after departing from Warsaw Chopin Airport (LHBP). During this phase of flight, cabin crew reported experiencing difficulty breathing and a sensation of pressure in their ears. An unusual whistling sound was also noted between rows 12 and 13 of the passenger cabin, followed by similar complaints from passengers.
While the Cabin Indication Module initially showed no anomalies, the flight crew subsequently experienced breathing difficulties and observed rapid fluctuations in cabin pressure. Notably, the MASTER WARNING "CABIN PRESS" did not activate. The aircraft was climbing at a vertical speed of approximately 1,000 ft/min (not exceeding 2,000 ft/min) in VS mode. In response to the situation, the crew performed the emergency descent memory items from the Quick Reference Handbook (QRH) and descended to FL100. The aircraft then returned to LHBP for landing.
Following the landing, the aircraft was transferred to technical services. Due to noise restrictions at LHBP, engines were only permitted to run for 15 minutes, which was sufficient only to prepare the aircraft for a ferry flight to Warsaw Modlin Airport (EPWA). This ferry flight was conducted at FL100 under the Minimum Equipment List (MEL 21-30-6).
The investigation
Technical inspections were conducted upon the aircraft's arrival at EPWA. Maintenance personnel performed three pressure tests and inspected the valves after cleaning them, but these procedures failed to reveal any malfunctions in the pressurization system. Additionally, the investigation identified a secondary technical issue: a #2 DC GEN CAUTION LIGHT, which the crew had logged after landing at LHBP. The captain noted this light appeared after engine start but believed it had no impact on aircraft systems and allowed for continued flight, though this action was inconsistent with the operator's standard operating procedures.
Findings
- The most probable cause of the incident was a temporary malfunction of the aircraft pressurization system.
- The investigation could not definitively establish the exact cause of the pressure fluctuations.
- The crew's decision to continue the flight following the appearance of the #2 DC GEN CAUTION light was not in compliance with the operator's operational procedures.