ICAO and IATA have introduced the following amendment to Annex 6, Aircraft Operations and Doc.4444 PANS-ATM, effective 15 November 2012. The amendment introduces new standard 'MINIMUM FUEL' and 'MAYDAY FUEL' R/T phraseology for pilots and ATC controllers to avoid confusion.
Minimum Fuel
The Commander/PIC shall advise ATC by declaring 'MINIMUM FUEL', when it is anticipated that the amount of fuel remaining at landing at the airport of intended landing, based on the current ATC clearance or EAT is approaching the planned final CFP Reserve Fuel.
This indicates to the controller that the aircraft, whilst it is operating normally, all planned airport options have been reduced to the specific airport of intended landing and any change to the existing clearance may result in landing with less than the planned final CFP Reserve Fuel.
This is not an emergency situation but an indication that an emergency situation (MAYDAY FUEL) is possible should any additional delay occur. The declaration of 'Minimum Fuel' requires the controller to keep the Commander/PIC informed of any delays.
MAYDAY Fuel (Emergency Fuel)
The Commander/PIC shall inform ATC by declaring 'MAYDAY MAYDAY MAYDAY FUEL' when it is assessed that the aircraft will land with less than CFP Reserve Fuel at the nominated destination airport. This is an emergency and the aircraft shall be given priority over other traffic in the landing sequence.