Aviation Investigation Report A98H0003
2.16 Factors Influencing Pilot Decision Making during Diversion
When the pilots started their descent toward Halifax at 0115:36, they had assessed that they were faced with an air conditioning smoke anomaly that did not require an emergency descent. Based on the perceived cues, they took steps to prepare the aircraft for an expedited descent, but not an emergency descent and landing.
The pilots were unfamiliar with the Halifax International Airport and did not have the approach charts readily available. The back-course instrument landing approach to Runway 06 was not pre-programmed into their flight management system (FMS). The pilots knew that they would have to take additional time to familiarize themselves with, and set up for, the approach and landing. They were given the weather information by the crew of an overflying aircraft, but did not know the runway lengths or orientation. Having the runway and instrument approach information available is normal practice and is important in carrying out a safe approach and landing, particularly at an unfamiliar airport at night.
In addition to these flight management circumstances, the pilots were aware that the meal service was underway, and that it would take some time to secure the cabin for a safe landing. Given the minimal threat from what they perceived to be air conditioning smoke, and the fact that there were no anomalies reported from the passenger cabin, they would likely have considered there to be a greater risk to the passengers and cabin crew if they were to conduct an emergency descent and landing without having prepared the cabin and positioned the aircraft for a stabilized approach and landing. It can be concluded that the pilots would have assessed the relative risks differently had they known that there was a fire in the aircraft.
The pilots also knew that the aircraft was too heavy for landing without exceeding the maximum overweight landing limits for non-emergency conditions. This would have been viewed as posing some risk, although it can be assumed that it would not have deterred them from continuing for an immediate landing, and dumping fuel during the landing approach, if they had perceived a significant threat to the aircraft. Coincident with their declaration of an emergency condition, the flight crew indicated that they were starting to dump fuel and there are indications that they did so.
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