CMF Call Sign FAQs

FAQ (Frequently Asked Questions)

What is the COMPASSION Call Sign?

The COMPASSION call sign and it’s three-letter designator CMF is intended to clearly identify routine ambulatory patient transport and other public service missions conducted by volunteers.The COMPASSION call sign was assigned to the Air Care Alliance as an organization that promotes public benefit flying in 1999.

What kind of flights can COMPASSION be used on?

COMPASSION and its associated three-letter identifier CMF are to be used to identify aircraft conducting bona fide nonprofit public benefit flying missions. This may include:

  • transporting individuals for health care, diagnostics, or treatment;
  • transporting blood, tissues, organs, or medical supplies; 
  • transporting emergency personnel, equipment, and supplies in time of emergency or public need; 
  • performing habitat or environmental survey or other missions in support of environmental objectives;
  • transporting rescue animals or wild animals needing relocation; 
  • and in general conducting non-profit flying operations serving the public interest, especially those conducted by volunteers.

COMPASSION must not be used for routine personal, business, or commercial flights. COMPASSION must not be used for positioning or ferry flights when during the times of flight an actual public benefit flying mission is not being conducted; EXCEPT that it may be used when there is a demonstrable need for appropriate (but not priority) handling by ATC.

What’s Changing?

Over the years, ACA has permitted VPOs use of the call sign through a specific filing process whereby a pilot enters the three-letter designator CMF on their flight plan, followed by the last three characters of their tail number. That procedure will no longer by authorized after December 15th, 2019. Pilots wishing to continue use of COMPASSION must be members of ACA authorized groups and they must register for a new, unique call sign through ACA.

Why the Change?

The change to the COMPASSION call sign process has to do with ADS-B implementation and FAA changes to call sign usage requirements.

Beginning January 1, 2020, ADS-B Out transponders will be required for all aircraft in airspace where transponders are mandatory today. This creates additional considerations for call sign usage.

The FAA issued an advisory circular containing updates to requirements and procedures for the use of aircraft call signs in the national airspace system.  The previous method of filing CMF did not meet these criteria. Therefore, new and unique call signs that meet FAA and ICAO requirements will be assigned by ACA to qualifying pilots who request one.

What is ACA's Role?

As the administrator of the COMPASSION call sign, the Air Care Alliance has worked with the FAA on behalf of public benefit flying organizations and volunteer pilots to develop new unique COMPASSION call signs which will be compatible with ADS-B out and FAA call sign usage requirements. ACA will assign these call signs, on request, to each qualified participating pilot for use on public benefit flights.

Can I Use the CMF call sign COMPASSION?

YES, if your public benefit flying group has been authorized to use the new call signs and you have requested and been assigned a new one.  The old filing procedure for using the COMPASSION call sign must not be used after December 15, 2019.  You may request your new call sign online IF you fly for a group authorized to use it and if you follow all the guidelines for use.

How does a volunteer pilot group become an authorized user?

The process is simple! In order to become an authorized user of the call sign, a group needs to sign two forms: 

The Air Care Alliance Affirmation (found on page 1 of the Membership Form). A group does NOT need to be a member of ACA to be an authorized user, but does need to agree to the affirmation.

FAA Security Agreement – The FAA requires that the ACA must obtain a security agreement before allowing third-party use of their call sign. Note: The security agreement requires that authorized groups maintain 24/7 points of contact on their website; however, please note that in the event the FAA requires information, they will contact ACA first and generally during business hours. Only in the rare event of an emergency will groups be contacted.

How do pilots register for a call sign?

Pilots who are members of an authorized group may register for their individual COMPASSION call sign by completing a simple form here. Once your member status is validated, you will be issued your call sign by email. This may happen automatically or may take several business days depending on the group you belong to.

Who should register for a call sign?

Active pilots of ACA authorized groups who are eligible to serve as PIC should register for a call sign. Please do not register for a call sign if you are a Mission Assistant (co-pilot) or otherwise not qualified to act as PIC for your organization. 

Additionally, your aircraft should be equipped with an ADS-B Out unit that is programmable by the pilot. Most 1090ES ADS-B Out transponders and some 978 UAT ADS-B transceivers allow pilots to edit the call sign. Sometimes that capability must be enabled or unlocked by an avionics shop. You should ensure that your aircraft is properly equipped before registering for a call sign.

Will the COMPASSION call sign work with an ADSB-Out transponder?

Yes or no, depending on your ADS-B out transponder.  You must have a model that provides for modifying and inputting a call sign appropriate for your mission since ADS-B broadcasts a call sign as programmed in an aircraft.  Many models can do this now, but this ability must be enabled at an avionics shop either during installation or later.  The call sign you program into the unit must exactly match the call sign you enter on your ICAO flight plan, if you filed a plan.  The call sign MUST conform to the new ICAO International call sign requirements as detailed in the procedures.

Will pilots be assigned a different call sign for each organization they fly for?

No. Pilots will only be assigned one COMPASSION call sign which can be used with any ACA Authorized group. 

Note: The CMF call sign is separate from the NGF or “Angel Flight” call sign. Pilots who fly for Angel Flight organizations that use NGF will keep their NGF call signs for use on Angel Flight missions.

Why can’t I find the group I fly for in the selection list when I register for a call sign?

Volunteer pilot groups must be authorized by the ACA to permit their pilots use of the COMPASSION call sign. If the group you fly for is not listed, it means they are not yet an ACA authorized user. They may have decided not to use COMPASSION or have simply not yet completed the authorization process. Please contact your group for more information.

Why should I use the COMPASSION call sign?


The COMPASSION call sign is intended to clearly identify routine ambulatory patient transport and other public service missions conducted by volunteers including: animal transport, environmental flights, disaster response and other non-profit flying that serves the public interest.
Using the COMPASSION call sign has many benefits for the pilot, the organizations they fly for, as well as ATC.
  • COMPASSION allows pilots to clearly identify to ATC as a bona fide public benefit flight.
  • Gives pilots access to special handling by ATC (better routing, altitude changes, etc.)
  • Provides a measure of safety and security for passengers who may have special needs due to medical reasons.
  • Encourages pilots to file a flight plan or use flight following on charitable flights which allows for better tracking and more efficient mission coordination.
  • Can provide authorization for flight operations during disaster response flights.
  • Increases the value and awareness of public benefit flying within the aviation community!

How do I use the COMPASSION call sign?

Procedures for use of the COMPASSION call sign may be found here. Please read and follow these instructions carefully.