Diversion Decision with a Suspected Fuel Leak
You are at FL310, 1 hour 10 minutes from destination, with 3.2 tonnes of fuel. The flight plan required 2.8 tonnes at destination, giving a 0.4-tonne margin. The fuel quantity indication has begun to fluctuate and the totaliser shows a 300 kg discrepancy over the last 20 minutes. You suspect a leak. The weather at destination is fine, but the nearest alternate is 25 minutes away with a 1,200 m runway and no ILS. A closer airport is 12 minutes away but has a 1,600 m runway and an ILS. Your company requires a 30-minute final reserve.
1. Calculate the fuel situation and decide whether to divert.
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At the current burn, the 300 kg discrepancy over 20 minutes suggests an additional loss of about 900 kg per hour if it continues. With 3.2 tonnes and 1 hour 10 minutes to destination, you would land with roughly 3.2 minus the normal burn (say 1.6 tonnes) minus the leak (about 1.05 tonnes), leaving about 0.55 tonnes - below the 0.4-tonne margin plus 30-minute reserve. The indication is unreliable, so treat the lower figure as real. The safer decision is to divert to the closer airport with the ILS and longer runway, land with fuel to spare, and have the leak investigated. The alternate 25 minutes away has a short runway and no ILS, adding risk. Declare a fuel emergency if the situation worsens, and keep ATC informed.
2. What cognitive biases could affect this decision, and how do you counter them?
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Plan-continuation bias: you have a destination and a schedule, and the fuel figure is ambiguous, so there is a temptation to press on and 'see how it goes'. Sunk-cost thinking: the time already flown makes diversion feel wasteful. Optimism bias: the discrepancy might be an indication fault, so the leak might not be real. Counter these by treating the worst credible case as the planning case, setting a hard decision point (for example, divert if the discrepancy exceeds a set threshold or if fuel falls below a calculated figure), and using a structured tool such as a fuel checklist. Involve the other pilot and state the reasoning aloud. The cost of an unnecessary diversion is small; the cost of a fuel emergency is not.