Why is there unusable fuel in an aircraft?

Aircraft have a certain amount of unusable fuel because in certain flight attitudes some of the total fuel can become inaccessible, particularly with low fuel levels. Unusable fuel is really a safety mechanism to ensure that the engine is properly fed fuel in all phases of flight.

Why fuel tank leak is major concern for aircraft?

Any hot bleed air leakage could result into a loss of engine thrust and in order to compensate, the fuel controller increases the fuel flow to the engine, resulting in higher operational costs. Therefore, it is important, to also perform a leak check on the pneumatic ducts before aircraft departure.

How do you get unusable fuel?

Look at the Pilot’s Operating Handbook (POH) or installed placards on most airplanes and you’ll find a notation about “unusable fuel.” Unusable fuel is that fuel in the tank(s) that is not considered to be accessible for running the engine(s).

What is the difference between usable and unusable fuel?

In aviation, usable fuel is the fuel on board an aircraft that can actually be used by its engines. The unusable fuel figure is calculated for an aircraft fuel tank in “the most adverse fuel feed condition occurring under each intended operation and flight maneuver involving that tank”. …

How can leaks in a fuel tank be discovered?

Releases are detected in various ways. Leak detection equipment may signal a release, or unexpected water may be detected in a tank. Newer UST systems have automatic tank gauging systems that can immediately identify a discrepancy using electronic measurement sensors and sound an alarm.

Why are aircraft fuel tanks Pressurised?

Each tank is vented (or pressurised) to allow air into the tank to take the place of burned fuel; otherwise, the tank would be in negative pressure which would result in engine fuel starvation. A vent also allows for changes in atmospheric pressure and temperature.