The Incident as a Situational example

Your twin-engine passenger airplane departs from a European airport for a short scheduled flight. It has previously been assigned as reserve for an aircraft on a longer flight which ended up taking place normally, and thus is loaded with 8.5 tons (17,000 lb) of fuel. This quantity is more than enough for the short 50-minute flight, which requires only 4.7 tons (9,400 lb). Therefore you do not request a top-up. The takeoff is uneventful and 12 minutes into the flight, on reaching cruise altitude, your attention is drawn to a fuel warning: the left wing tank is lighter than its counterpart on the right wing by 1.5 tons (3.000lb). All engine parameters are nominal.