What happened
On October 24, 2007, a Pilatus PC-12-45, registration EC-JFO, was climbing through FL220 near the BENOT and MILPA navigation points when the pilot experienced abnormal fatigue. The crew observed that the cabin differential pressure had dropped to approximately 3 PSI, significantly below the expected maximum of 5.75 PSI. As the cabin altitude continued to rise at a rate of 1500 ft/min, the pilot ordered the use of oxygen masks and an emergency descent.
The crew notified air traffic control and requested a diversion to Geneva. Following instructions, they descended through FL160 and eventually reached FL100, at which point the cabin altitude matched the aircraft altitude, allowing the crew to remove their masks. The aircraft landed safely at Geneva-Cointrin airport without further incident.
Six days later, during a subsequent flight from Geneva to Barcelona, the crew encountered a similar loss of pressurization while climbing through 5000 ft and returned to Geneva for inspection.
The investigation
The investigation focused on why the pressurization system failed following an annual maintenance check performed by the manufacturer just one week prior. Technical inspections revealed that a bleed air hose in the engine compartment was not properly secured to the cabin wall. This loose connection prevented sufficient compressed air from reaching the cabin, which also resulted in reduced airflow to the cockpit windshields.
Investigators also examined the operational procedures used by the crew. While the crew managed the emergency effectively, it was noted that the short checklist they were utilizing did not include a specific requirement to monitor cabin pressure during the climb phase.
Findings
- The primary cause of the serious incident was a failure in the cabin pressurization system following an annual inspection.
- A contributing factor was that the crew's version of the short checklist lacked a check point for monitoring cabin altitude/pressure during climb.
- The technical failure was caused by an improperly secured air supply hose within the engine compartment.
- The crew's decision-making and application of emergency procedures were appropriate for the situation.