In-flight fuel management
39.—(1)  The pilot-in-command of a relevant aircraft must monitor the amount of usable fuel remaining on board to ensure the amount of usable fuel is not less than the amount of fuel required to proceed to an aerodrome or landing site (as applicable) where a safe landing can be made, with the planned final reserve fuel remaining.
(2)  The pilot-in-command of a relevant aircraft must advise the appropriate air traffic control unit of a minimum fuel state by declaring “MINIMUM FUEL” when, after committing to land at a specific aerodrome or landing site (as applicable), the pilot‑in‑command calculates that the aircraft may land with less than the planned final reserve fuel if there is —
(a)any change to the existing clearance to that aerodrome or landing site; or
(b)any other air traffic delay.
(3)  The pilot-in-command of a relevant aircraft must declare a situation of fuel emergency by broadcasting “MAYDAY MAYDAY MAYDAY FUEL” when the calculated usable fuel estimated to be available upon landing at the nearest aerodrome or landing site (as applicable) where a safe landing can be made is less than the planned final reserve fuel.