Do I have to declare an emergency if I cut into fuel reserves?

Question

In another question, I wrote

You only need to plan for regulatory reserves. You don't actually have to land with them

and @Jan replied:

you have to declare emergency if you do cut into them though and that will quite probably get you an investigation

I have never heard that you must declare an emergency if you cut into your reserves (regardless of the stage of flight), and I'm wondering if there is any regulation to back it up.

The only reg that I could find that comes close is NTSB 830, which lists a set of criteria for notifying the NTSB within 10 days:

(a) An aircraft accident or any of the following listed serious incidents occur:

(1) Flight control system malfunction or failure;

(2) Inability of any required flight crew member to perform normal flight duties as a result of injury or illness;

(3) Failure of any internal turbine engine component that results in the escape of debris other than out the exhaust path;

(4) In-flight fire;

(5) Aircraft collision in flight;

(6) Damage to property, other than the aircraft, estimated to exceed $25,000 for repair (including materials and labor) or fair market value in the event of total loss, whichever is less.

(7) For large multiengine aircraft (more than 12,500 pounds maximum certificated takeoff weight): (a bunch of other things)

I'm interested in the answer for Parts 91, 135, and 121, under FAA regulations.

Answer 1

There seems to be no regulations that require decleration of emergency in case of using reserve fuel. US DoT InFO 8004 specifically discusses this:

Emergency Fuel. Although not defined in the AIM or Federal aviation regulations, the industry-wide connotation typically associated with the term “Fuel Emergency” is:

The point at which, in the judgment of the pilot-in-command, it is necessary to proceed directly to the airport of in tended landing due to low fuel. Declaration of a fuel emergency is an explicit statement that priority handling by ATC is both required and expected.

Noting that pilot declaring minimum fuel is not an emergency,

The act of using a portion of the reserve fuel assigned to a flight is not, in its self a cause to declare a minimum fuel state with the controlling agency. Regulations require reserve fuel to enable aircraft to maneuver, due to unforeseen circumstances. Many aircraft safely arrive at their destination having used a portion of the fuel designated as reserve. There is no regulatory definition as to when, specifically, a pilot must declare “minimum fuel” or a fuel emergency. Air carriers typically develop such guidance for their pilots and include it in their General Operations Manuals; such guidance generally falls along the following lines:

•Declare “minimum fuel” when, in your best judgment, any additional delay will cause you to burn into your reserve fuel.

•Declare a fuel emergency at the point at which, in your judgment, it is necessary for you to proceed directly to the airport at which you intend to land. Declaration of a fuel emergency is an explicit statement that priority handling by ATC is necessary and expected.

(Emphasis mine)

Answer 2

No, you don't, but per the AIM you should declare an emergency if you need priority for landing.

There may be some confusion here between declaring "minimum fuel" to ATC, and declaring an emergency. The AIM 5-5-15 says:

1. Advise ATC of your minimum fuel status when your fuel supply has reached a state where, upon reaching destination, you cannot accept any undue delay.
2. Be aware this is not an emergency situation, but merely an advisory that indicates an emergency situation is possible should any undue delay occur.

[...]

5. If the remaining usable fuel supply suggests the need for traffic priority to ensure a safe landing, you should declare an emergency due to low fuel and report fuel remaining in minutes.

But in general there's no regulation or rule that I can find that says when a pilot must declare an emergency. The general guidance from the AIM 6-1-2 is that pilots are expected to declare an emergency when a state of distress exists. The ATC orders 10-1-1 are a little more specific:

A pilot who encounters a Distress condition should declare an emergency by beginning the initial communication with the word “Mayday,” preferably repeated three times. For an Urgency condition, the word “Pan-Pan” should be used in the same manner.

As for what distress actually means, the Pilot/Controller Glossary simply says:

DISTRESS− A condition of being threatened by serious and/or imminent danger and of requiring immediate assistance.

It's unlikely that cutting into fuel reserves by itself would constitute a "serious or imminent danger" (which is why "minimum fuel" isn't an emergency) but on the other hand if the pilot is also unsure of his position or has other issues to deal with, then it might still be the best thing to do.

Answer 3

One time after WX and extended vectors (over 50 minutes of additional delay), I was almost ready to cut into my night IFR with alternate reserves plus my modest buffer. Not the legal minimum, but my minimum. I told Baltimore Approach that I was declaring "MINIMUM FUEL." I was asked how much fuel I hand on board, which I provided in minutes. I was also asked for souls on board. They handed me to Dulles Approach, explaining that Dulles had better coverage for KGAI, even though KGAI was in their airspace (or sector).

My rules for the flight were that if I had any more delaying vectors I would have to divert, and given the WX, diversion would potentially be problematic. I had been cleared to KGAI, but if I was delayed further I would have to land somewhere else.

To be clear, I did not intend to declare an emergency, but the controllers treated it that way. Dulles gave me a dedicated controller and kid glove handling to KGAI, and cleared me for the NDB approach. He also called the FBO to verify I made it in, I was told by the line guy. The Dulles controller had asked me to call him when I landed, so I called Baltimore on Clearance Delivery, and asked them to tell Dulles I landed and appreciated the assistance.

It was raining hard, but I took the time to dip the tank, because I wanted to know exactly where I was fuel wise. I was within 1 gal of my estimated fuel, which was 1:45 plus unusable, as I was at night, IFR, and with weather that required an alternate.

There was never any paperwork. The following week, when I got home, I sent both Baltimore and Dulles a thank you letter for their handling of things. To this day I use this flight as an example to students of the power of "MINIMUM FUEL."

Answer 4

In Australia, the answer is yes if you expect to land with less than the fixed fuel reserve. CASA 29/18 – Civil Aviation (Fuel Requirements) Instrument 2018 s7(5):

The pilot in command must declare a situation of emergency fuel when the calculated usable fuel predicted to be available upon landing at the nearest aerodrome where a safe landing can be made is less than the fixed fuel reserve for the flight. The pilot in command must declare an emergency fuel state by broadcasting MAYDAY, MAYDAY, MAYDAY FUEL.

https://www.legislation.gov.au/Details/F2018L00644/Html/Text#_Toc514142500