Two-way radio communication failure procedures for IFR operations are outlined in Part 91.185. Unless otherwise authorized by ATC, pilots operating under IFR are expected to comply with this regulation. Expanded procedures for communication failures are found in the AIM. Pilots can use the transponder to alert ATC to a radio communication failure by squawking code 7600. [Figure 3-25 on page 3-20] If only the transmitter is inoperative, listen for ATC instructions on any operational receiver, including the navigation receivers. It is possible ATC may try to make contact with pilots over a VOR, VORTAC, NDB, or localizer frequency. In addition to monitoring NAVAID receivers, attempt to reestablish communications by contacting ATC on a previously assigned frequency, calling a FSS or Aeronautical Radio Incorporated (ARINC).

The primary objective of the regulations governing communication failures is to preclude extended IFR no-radio operations within the ATC system since these operations may adversely affect other users of the airspace. If the radio fails while operating on an IFR clearance, but in VFR conditions, or if encountering VFR conditions at any time after the failure, continue the flight under VFR conditions, if possible, and land as soon as practicable. The requirement to land as soon as practicable should not be construed to mean as soon as possible. Pilots retain the prerogative of exercising their best judgment and are not required to land at an unauthorized airport, at an airport unsuitable for the type of aircraft flown, or to land only minutes short of their intended destination. However, if IFR conditions prevail, pilots must comply with procedures designated in the CFRs to ensure aircraft separation.

If pilots must continue their flight under IFR after experiencing two-way radio communication failure, they should fly one of the following routes:
  • The route assigned by ATC in the last clearance received.
  • If being radar vectored, the direct route from the point of radio failure to the fix, route, or airway specified in the radar vector clearance.
  • In the absence of an assigned route, the route ATC has advised to expect in a further clearance.
  • In the absence of an assigned or expected route, the route filed in the flight plan.

It is also important to fly a specific altitude should two-way radio communications be lost. The altitude to fly after a communication failure can be found in Part 91.185 and must be the highest of the following altitudes for each route segment flown.

  • The altitude or flight level assigned in the last ATC clearance.
  • The minimum altitude or flight level for IFR operations.
  • The altitude or flight level ATC has advised to expect in a further clearance.
In some cases, the assigned or expected altitude may not be as high as the MEA on the next route segment. In this situation, pilots normally begin a climb to the higher MEA when they reach the fix where the MEA rises. If the fix also has a published minimum crossing altitude, they start the climb so they will be at or above the MCA when reaching the fix. If the next succeeding route segment has a lower MEA, descend to the applicable altitude ? either the last assigned altitude or the altitude expected in a further clearance ? when reaching the fix where the MEA decreases.