Description

Sleeping receiver is the term used to describe incidents when the radio apparently goes dead so that no incoming calls are heard, either those directed to the flight or those between ATC and other flights. Usually, the situation continues until the aircraft transmitter is keyed - often because the pilots have noticed the silence and wish to check their receiver; thereafter, radio operation is normal.

When this circumstance first began to be reported, the number of reports was low but there was some increase in reports for a period thereafter. After initial reports from UK airspace, the geographical extent of such occurrences appeared to expand. Deficiencies in one particular model of airborne transceiver and the introduction of offset carrier wave transmissions in some ACC sectors served by multiple ground transmitters was eventually associated with some reported events.

It seems likely that some cases of “sleeping receiver” go unreported by flight crew, possibly because those involved suspect that communication was lost through some other cause (e.g. poor radio propagation, their own inattentiveness, or equipment mishandling). The enhanced recording capability of modern quick access flight data recorders used for operational monitoring, which now show the exact timings of RTF frequency selection and the timings of aircraft radio transmissions by crew position and frequency, appears to have deterred some reports formerly 'identified' as sleeping receiver events of unknown origin.

The sleeping receiver phenomenon was extensively investigated by the UK CAA following the initial reports from UK airspace and by UK registered aircraft operating outside the UK elsewhere, but despite much attention to various possible origins of the phenomenon, no predominant single cause was found.

The subject is reviewed in EUROCONTROL Air-Ground Communication Briefing Note No 3: Loss of Communication, paragraphs 4.2 to 4.5.

Further Reading

EUROCONTROL European Action Plan for Air Ground Communications Safety:

• AGC Briefing Note 3 - Loss of Communication;
• AGC Safety Study - Causes and Recommendations;