Why is fuel quantity expressed in flight hours Going through a few aircraft documentaries online, I've noticed the thing that they usually express the fuel quantity in flight hours.
Ex - A 747 burns 4 litres of fuel every second. So with a ton of fuel, it'll stay in air for roughly 3-4 minutes.
Why are flight hours a necessary term while consider fuel quantity? I mean shouldn't they be worried about how much distance they can cover in an emergency to reach an airport, instead of how long they can stay in the air?
Seems a question related to endurance but couldn't find any proper explanation
It’s primarily due to wind.
Aircraft move through the air at a certain speed, which makes it tempting to give range in miles (or kilometers), but the air itself is moving as well, and often at a large enough fraction of the aircraft’s airspeed that it materially affects range across the ground.
For instance, say you have a Cessna 172 with four hours of fuel (plus reserves) and a cruise speed of 110kt. With a 30kt tailwind (140kt ground speed), your range is 560nm. But going the opposite direction with a 30kt headwind (80kt ground speed), your range is only 320nm—just over half as far!
To make it even more complicated, the winds will have different directions and speeds at different altitudes and locations, and all of that changes over time too, which is one of the reasons pilots (or dispatchers) have to carefully plan each flight’s route and fuel load, even for a “fixed” daily route between the same two airports.