Few threats to an aircraft in cruise hold the same dread as cabin fire. Combustion is a complex process that seems to defy its purely physical and chemical nature to give the impression of a living, breathing, ravenous entity. In flight, there is only one certainty about fire - the situation never, ever gets better.

That fundamental aspect is illustrated by the systematic deterioration, chronicled by United Arab Emirates investigators, that engulfed a UPS Boeing 747 freighter barely 20min out of Dubai last September.

And 20min is an eternity where fire is concerned. The blaze that overtook Swissair 111 in 1998, forcing a rethink on operational procedures in the face of fire, had been just a hint of smoke 20min before the Boeing MD-11 was lost off the Canadian coast.

Swissair 111 changed pilots' mindset toward fire threats, setting a benchmark with regard to survival time. If the countdown clock started at 20min, it was reasoned, you had better be on the ground in 10.

Which brings us to a crucial question at the heart of the UPS inquiry: given that Dubai was 50% further away than Doha, what prompted the crew to opt for the longer sector while, below deck, a smouldering source was blossoming into flame? Whether a diversion to Doha might have altered the outcome has yet to be fully analysed. But in flight, distance equates to time. And to a fire at altitude, time is simply another form of fuel.

Source: Flight International