The Marine Corps has issued immediate guidance to all aviation units after identifying a recurring problem: pilots and operators are turning off the altitude reporting function (Mode C) on their transponders, apparently believing it supports Emissions Control (EMCON) procedures. It does not. Turning off Mode C alone has no EMCON value, and it causes real problems, both in the tactical picture and in the broader airspace.
Heads up: Turning off Mode C is not a valid EMCON procedure. Stop doing it.
Who it affects
Every Marine aviation unit operating a military platform equipped with an Identification Friend or Foe (IFF) transponder or a civil transponder. This is directed at operators and the units responsible for training them.
What you need to do
- Keep Mode C enabled at all times. Do not deselect it under any circumstances during normal or EMCON operations.
- For actual EMCON, disable Mode 3/A instead. Disabling Mode 3/A cuts replies to both Mode 3/A and Mode C simultaneously. That is the correct procedure.
- The only time you may disable Mode C is when an Air Traffic Control (ATC) authority explicitly directs it because of a verified error in your platform's pressure altitude reporting.
- Units must push this guidance to all operational aviation personnel.
Key dates
- Effective immediately upon release (16 June 2026)
The official version
This guidance is MARADMIN 278/26. It references two Joint Staff documents: a memorandum on Mode C guidance (15 May 2026) and an information paper on Mode C (1 May 2026). Contact the POC for copies: LtCol Joseph Goodrich at joseph.goodrich@usmc.mil or 703-614-3606.
This is written by a reservist, for reservists. It is not an official publication of HQMC or MARFORRES. Always verify guidance with your command or unit S-1 before acting on any article or summary.