After I wrote my article last month about some of the mindsets that can get us into trouble, I found an excellent example of one of those situations. Air Transat Flight TS236 was an Airbus A330 that was on its way from Toronto to Lisbon. The discovery of metallic particles in the oil system about a week earlier had led the airline to do a precautionary engine change. A manufacturer’s service bulletin recommended a change to how a hydraulic line was connected in order to provide more clearance to a nearby fuel line. All of Air Transat’s engines had this modification, but the replacement engine had not been modified.
The lead mechanic tried to find the service bulletin but was unsuccessful due to computer problems. Finally a supervisor came up with a way to complete the installation by spreading the lines apart to create more space, and the installation was completed. Over the next few days normal vibration and flexing caused this clearance to be lost, and the hydraulic line started rubbing against the fuel line, eventually causing a leak during the flight to Lisbon. Initially the leak was a relatively moderate 1,000 pounds per hour, and the crew didn’t notice anything wrong.
