What happened
On November 24, 2012, a Boeing 737-700 NG, registration HP-1371 CMP, operating as Copa Airlines Colombia flight 7472 from Bogotá to Cartagena, experienced a cabin decompression during its climb. The aircraft was operating with a deferred maintenance item under MEL 36-05 regarding the left engine bleed system.
During the ascent, the crew deactivated the Auxiliary Power Unit (APU) while below the altitude specified in the MEL procedures. As the aircraft climbed through flight level 210, the crew experienced an unexpected increase in cabin altitude, followed by a loss of cabin pressure and the deployment of oxygen masks for the 113 passengers and 5 crew members. The pilot declared an emergency and initiated an emergency descent, returning the aircraft to Bogotá (SKBO), where it landed safely without injuries or further damage.
The investigation
The GRIAA investigation examined the aircraft's maintenance history, which revealed several recent entries regarding unusual odors in the cabin and previous pressurization issues, including a reported leak near an emergency exit. The investigation also reviewed the flight crew's actions and their adherence to the Minimum Equipment List (MEL).
Investigators found that while the crew had reviewed the MEL 36-05 procedures prior to the flight, they did not physically consult the document during the climb. The investigation established that the crew's execution of the procedures was incorrect; specifically, they shut down the APU at an altitude lower than required and failed to properly configure the air conditioning packs and the isolation valve as mandated by the MEL for the deferred bleed condition.
Findings
- The primary cause of the decompression was the improper operation of the procedures outlined in MEL 36-05 by the flight crew.
- The crew failed to consult the physical MEL document during the flight to verify the correct operational steps.
- The crew deactivated the APU at an altitude below the threshold specified for the deferred engine bleed system.
- The crew left the right air conditioning pack in the 'OPEN' position and the isolation valve in the 'CLOSED' position, deviating from the required configuration.
- The co-pilot had limited operational experience on the Boeing 737 NG type at the time of the incident.
Safety action
- The GRIAA recommended that Copa Airlines Colombia improve training procedures regarding the use and compliance with MEL operational actions, specifically emphasizing the necessity of consulting the MEL during transition and recurrent training courses.