What happened
On 02 January 2005, an Air Canada Boeing 767-375, registration C-FCAG, was performing a scheduled flight from Toronto to Santiago, Chile. Approximately nine and a half hours into the flight, while cruising at flight level 370, the crew received warnings of low fuel pressure from both boost pumps in the left main fuel tank. Within 45 seconds, the left engine flamed out. The crew declared a Mayday, initiated a descent, and successfully restarted the engine approximately 18 minutes later. The aircraft landed in Santiago without further incident, though a post-landing inspection revealed a severe fuel imbalance: the right tank contained 4700 kg of fuel, while the left tank was completely empty.
The investigation
The investigation focused on why the aircraft was dispatched with an incorrect fuel load and why the fuel imbalance went undetected. It was established that the aircraft arrived in Toronto with a significant discrepancy between the recorded fuel and the actual fuel on board. During refuelling, the fueller's records and the cockpit indications were inconsistent, and the crew manually adjusted the arrival fuel figures in the ACARS system to match the fueller's notes, inadvertently masking a shortage.
Investigators also examined the aircraft's maintenance history, which revealed a pattern of recurring failures in the fuel quantity indicating system (FQIS). Specifically, the left tank's fuel quantity indicator had been intermittently blanking out for several weeks. The investigation found that maintenance control had failed to properly identify these as recurring defects and had even incorrectly signed off certain defects as fixed when no work had been performed. Furthermore, a practice of using a weight to force the automated removal of Minimum Equipment List (MEL) entries from the tracking system was discovered in the maintenance control center.
Findings
- The aircraft was dispatched with a 5000 kg fuel shortage in the left main tank due to inaccurate fuel quantity indications and improper verification.
- A faulty wiring harness in the left wing caused the fuel quantity indicator to fail and caused the refuelling process to terminate prematurely.
- Maintenance control failed to effectively manage recurring fuel indication defects, leading to the aircraft being operated without necessary MEL restrictions.
- The crew did not perform the required manual fuel verification using measuring sticks, which would have detected the imbalance.
- Inadequate maintenance oversight and the circumvention of technical dispatch procedures allowed the aircraft to fly with an unserviceable FQIS and an unmonitored fuel imbalance.