FAA Warns Low-Altitude CPDLC Users of Coverage Gaps

June 6, 2025

The FAA recently issued an advisory about potential service interruptions on its Data Comm page to domestic enroute Controller Pilot Data Link Communications (CPDLC) users below 16,000 feet MSL.

The advisory mainly applies to general aviation piston and single-engine turboprop aircraft.

Currently, enroute CPDLC service availability is required above 16,000 feet, in addition to transition airspace around hub airports providing Data Link IFR Clearances (DCL). Service gaps could include interruptions of CPDLC connections between aircraft and ground stations, which could result in CPDLC message failures to ATC that could interfere with controller instructions, or pilot requests not being received by ATC.

These issues could result in undesirable safety concerns and increased ATC workload.

Richard J. Boll II, chair of NBAA’s Airspace and Flight Technologies Subcommittee, explained the current ground infrastructure, “provides a reasonable level of service availability of enroute CPDLC coverage east of the Mississippi down to 10,000 feet MSL. However, west of this area, enroute CPDLC coverage may not be continuously available at altitudes below 16,000 feet.” Boll added.

“These service gaps may also have an undesirable effect on aircraft CPDLC avionics performance,” which is constantly evaluated when using the enroute service, he said. “These evaluations measure the number of message failures from the ground to the aircraft. If a message failure is due to these gaps in signal coverage, that recorded failure could needlessly count against the aircraft’s enroute CPDLC performance, leading to its performance being deemed unacceptable for use in the US enroute CPDLC environment.”

Hence, a CPDLC failure on one aircraft could potentially reflect on other companies operating that same aircraft type. The agency says all operators are responsible for knowing individual avionics capabilities and FAA domestic airspace datalink communications requirements as documented in InFO 23008.

While the agency wants to encourage CPDLC at low altitudes, it has not provided pilots with specific guidance on this operational conundrum, which might lead some pilots to choose not to use CPDLC at low altitudes.

The FAA, L3Harris, and DCIT are trying to head off issues with avionics/airframes related to gaps in enroute CPDLC coverage rather than aircraft equipment. However, the future of low-altitude domestic CPDLC coverage away from major hub cities is somewhat in doubt because the two companies the FAA contracted with for initial infrastructure—AIRINC and SITA—have fulfilled their original service contracts.

Plans to create additional infrastructure supporting CPDLC away from major cities have not been announced.