What happened
On 21 February 2017, an Airbus A320, registration EC-HTD, operated by Vueling, was performing a scheduled domestic flight from Malaga-Costa del Sol Airport to Barcelona-El Prat Airport. The aircraft was carrying 176 persons, including 169 passengers and 7 crew.
During the initial climb through 1,600 ft, the flight crew received simultaneous warnings regarding the left engine bleed system and the associated air pack. Although the crew successfully reset the system, the warnings recurred while climbing through 12,000 ft. Consequently, the crew decided to limit the aircraft's maximum cruising altitude to FL300.
Upon reaching FL300, the aircraft experienced a second set of failures involving the right engine bleed valve and the number 2 cooling pack. The crew declared a MAYDAY and initiated an emergency descent to FL100. During the descent, the maximum cabin altitude reached 6,700 ft, and while oxygen masks were not required, the crew diverted the aircraft to Alicante Airport, where it landed safely at 21:08 local time.
The investigation
The investigation examined the aircraft's pneumatic and bleed systems, maintenance records, and the installation of components. Investigators reviewed the maintenance history of the engine pressure regulating valves (PRV) and the condition of the temperature limitation thermostats (TLT).
Technical inspections revealed that the left engine was equipped with an incorrect model of PRV (type-G instead of the required type-E) due to a component identification error in the Illustrated Parts Catalogue (IPC). While this incorrect installation was identified, investigators determined it was not the direct cause of the incident, as the part had functioned for 18 months without issue. The investigation also noted that the bleed regulation system is a closed system, which prevents the detection of component wear during routine inspections.
Findings
- The primary cause of the incident was the undetected degradation of the bleed regulation system components.
- The wear on the PRVs and TLTs was found to be higher than expected given the number of flight cycles.
- An incorrect model of pressure regulating valve was installed in the number 1 engine due to an error in the IPC.
- The aircraft's APU was inoperative and deferred according to the Minimum Equipment List (MEL) at the time of departure.
- The flight crew managed the emergency effectively, and coordination with Air Traffic Control facilitated a safe diversion.
Safety action
- REC 06/18: It is recommended that Airbus establish a scheduled maintenance task to ensure the operating ranges of components within the aircraft's bleed system are regularly checked.