R 161910Z JUN 26 MARADMIN 278/26 MSGID/GENADMIN/CMC AVN WASHINGTON DC// SUBJ/GUIDANCE ON IDENTIFICATION FRIEND OR FOE (IFF) ALTITUDE REPORTING (MODE C) CONTROL// REF/A/MSGID:DOC/JOINT STAFF WASHINGTON DC/YMD:20260515// REF/B/MSGID:DOC/JOINT STAFF WASHINGTON DC/YMD:20260501// NARR/REF A IS THE JOINT STAFF MEMORANDUM ON MODE C GUIDANCE. REF B IS THE JOINT STAFF INFORMATION PAPER ON MODE C.// POC/LTCOL/JOSEPH GOODRICH/TEL:703-614-3606/ EMAIL:[email protected]// GENTEXT/REMARKS/1. This MARADMIN provides critical guidance for all platforms equipped with IFF or civil transponders to address significant operational and safety concerns. 2. Background. A recurring issue has been identified where military operators deselect the altitude reporting (Mode C) function on their transponders. This action is often taken under the erroneous assumption that it is a valid Emissions Control (EMCON) procedure. Deselecting Mode C causes the transponder to report "unknown altitude," which creates serious safety risks, degrades the tactical picture, and negatively impacts air traffic control. 3. Guidance. Effective immediately, all units will adhere to the following: a. Do not deselect Mode C. Any military platform using an IFF transponder must ensure the altitude reporting (Mode C) control remains enabled at all times. Deselecting Mode C alone has no effect on achieving EMCON. b. EMCON procedures. For EMCON purposes, if a platform needs to secure Mode C replies, the operator must disable Mode 3/A, which disables replies to both Mode 3/A and Mode C. Mode C must remain enabled, even during EMCON. c. Exception. The only exception to this guidance is when explicitly directed by an Air Traffic Control (ATC) authority due to verified errors in the platform's pressure altitude reporting. 4. Impacts of incorrect procedures: a. Military operations: Disabling altitude reporting negatively impacts Combat Identification and the ability of C2 systems to maintain a coherent and accurate tactical picture. b. Civil aircraft safety: Nearby aircraft with Traffic Alert and Collision Avoidance Systems (TCAS) will receive erroneous traffic advisories, leading to unnecessary and potentially unsafe maneuvers. 5. Widespread dissemination of this guidance to all operational aviation units is required. 6. Release authorized by Lieutenant General William H. Swan,  Deputy Commandant for Aviation.//