The US "minimum fuel" radio call, versus "mayday"

It’s an official ICAO term and is used in Europe as well.

Annex 6:

4.3.7.2.2 The pilot-in-command shall advise ATC of a minimum fuel state by declaring MINIMUM FUEL when, having
committed to land at a specific aerodrome, the pilot calculates that any change to the existing clearance to that aerodrome may
result in landing with less than planned final reserve fuel.

Note 1.— The declaration of MINIMUM FUEL informs ATC that all planned aerodrome options have been reduced to a specific aerodrome of intended landing and any change to the existing clearance may result in landing with less than planned final reserve fuel. This is not an emergency situation but an indication that an emergency situation is possible should any additional delay occur.

Note 2.— Guidance on declaring minimum fuel is contained in the Fuel Planning Manual (Doc 9976).

It should be noted that Pilots should not expect any form of priority handling as a result of a “MINIMUM FUEL” declaration. ATC will, however, advise the flight crew of any additional expected delays as well as coordinate when transferring control of the aeroplane to ensure other ATC units are aware of the flight’s fuel state

And here is how it is worded in EHAM airport briefing (Jeppesen 10-1P10):

2.6. MINIMUM FUEL PROCEDURES
2.6.1. PILOT AND ATC PROCEDURE
- Pilots shall advise “minimum fuel” to ATC when the ACFT fuel supply has reached a state where the flight is committed to land at a specific APT and no additional delay can be accepted.
- ATC shall use this as advisory information which indicates that an emergency situation is possible, should any undue delay occur. The minimum fuel advisory implies no emergency situation and priority handling will not be provided.
- Amsterdam ACC will provide an expected approach time (EAT) or advise “no delay”. No delay means that the anticipated delay before or at the initial approach fix is not more than 2 minutes.
- On request SCHIPHOL Approach can provide the approximate distance to touchdown.
Note: Only when the pilot declares an emergency, radio call prefixed by MAYDAY (3x) for distress or PAN PAN (3x) for urgency, priority handling will be provided. Calls such as “low on fuel” have no status in the Amsterdam FIR.

To make things a little more strange, here is the “Guidelines for Controller Training in the Handling of Unusual/Emergency Situations” fuel-related page, which provides information and explanation or may indicate best practice.

Fuel Problems – Critical Fuel Status
May result in:
• Engine Failure (multi-engine)
• Engine Failure (single engine)
• Diversionary or Forced Landing
> Expect
• MAYDAY low on fuel emergency with imminent danger to ACFT
• PAN PAN minimum fuel ACFT needs priority handling
• Improper use of phraseology, verify actual fuel status (low on …, minimum … or
minimum diversion fuel)
> Remember
A ‘Acknowledge’ – S ‘Separate’ – S ‘Silence’ – I ‘Inform’ – S ‘Support – T ’Time’
• Keep ACFT high (save fuel)
• Avoid ATC-caused GO AROUND
• Inform landing aerodrome
• Ask if dangerous goods on board
• Ask for number of Persons On Board (POB)
• Clear RWY according to local instructions
• Keep safety strip clear
• Towing equipment on standby as appropriate
> If needed, inform pilot about:
• Next suitable aerodrome
• Aerodrome details as soon as possible
• WX information at landing aerodrome

As Ultranomad wrote, it’s not US specific. Just yesterday I came across it while looking for something else. It’s interesting to see how low on fuel are pilots willing to get. ICAO provides some guidance on when to declare fuel emergency as well (for IFR I believe you’re supposed to declare fuel emergency when you calculate that fuel on landing on the nearest suitable airport would be less than planned reserve, my emphasis).

Not just IFR flights. The proposed EASA rules incorporating the latest ICAO text are in NPA 2016-06(C)

NCO.OP.185 In-flight fuel management
(a) The pilot-in-command shall monitor the amount of usable fuel/energy remaining to ensure that it is not less than the
fuel/energy required to proceed to site where a safe landing can be made with the planned final reserve fuel/energy remaining.

(b) The pilot-in-command of a controlled flight shall advise the air traffic control (ATC) of a minimum fuel/energy state by declaring MINIMUM FUEL when, having committed to land at a specific aerodrome or operating site, the pilot calculates that any change to the existing clearance to land at that aerodrome or operating site, or other air traffic delays, may result in landing with less than the final reserve fuel/energy.

(c) The pilot-in-command of a controlled flight shall declare a situation of fuel/energy emergency by broadcasting MAYDAY MAYDAY MAYDAY FUEL when the usable fuel/energy estimated to be available upon landing at the nearest site where a safe landing can be made in accordance with normal operating procedures is less than the planned final reserve fuel/energy.

Does I understand correctly that if you will be close to reach the reserve fuel upon landing you should declare MINIMUM fuel and that if you will hit your reserve upon landing you should declare MAYADAY ?

jfw wrote:

Does I understand correctly that if you will be close to reach the reserve fuel upon landing you should declare MINIMUM fuel and that if you will hit your reserve upon landing you should declare MAYDAY ?

The way it was explained to me is as follows:

MAYDAY means “I will land with less than final reserve fuel”
MINIMUM FUEL means “If you delay me I will declare a MAYDAY”

Which means that you should look for other suitable aerodromes that are closer before declaring instead to press on to your destination AFAIU.

Aviathor wrote:

Which means that you should look for other suitable aerodromes that are closer before declaring instead to press on to your destination AFAIU.

Certainly (AIUI). As longs as there are suitable aerodromes (if we leave other “operating sites” out of it) where you can land with planned reserves, it’s not an emergency. Not diverting when it’s clear to you that continuing will result in an emergency isn’t IMHO exactly a show of good airmanship. Also notice the word committed when it comes to declaring minimum fuel. To me it means that you no longer have a choice or other options are even worse.

Question is whether fuel not being available is enough to make it unsuitable. I guess not but it would certainly be PITA. And it wouldn’t be a nice dilema to have – pressing on and probably having to declare an emergency or landing and being stranded for who knows how long. Which might lead to the third option – not declaring the emergency when I’m supposed to.

PS: I’m wondering whether I’m interpreting committed too strictly. That part of Annex 6 Ultranomad posted speaks only of planned aerodrome options.

Aviathor wrote:

Which means that you should look for other suitable aerodromes that are closer before declaring instead to press on to your destination AFAIU.

Yes, that’s the point of NCO.OP.185(a). It’s intended to be three layers of protection: “monitor, minimum fuel call, mayday fuel call”.

Martin wrote:

Question is whether fuel not being available is enough to make it unsuitable. I guess not but it would certainly be PITA. And it wouldn’t be a nice dilema to have – pressing on and probably having to declare an emergency or landing and being stranded for who knows how long. Which might lead to the third option – not declaring the emergency when I’m supposed to.

PS: I’m wondering whether I’m interpreting committed too strictly. That part of Annex 6 Ultranomad posted speaks only of planned aerodrome options.

“Safe landing” is explained in the GM. You’re expected to review all the landing options you have that can be performed in accordance with normal operating procedures (runway length adequate, weather above AOM etc.). I don’t think the lack of availability of fuel would prevent a safe landing, however inconvenient.