On 27th May 2015, the AirNav Area Control Centre (ACC) in Shannon introduced a listening squawk in the Shannon Flight Information Region (FIR). The listening squawk for Shannon Flight Information Service (FIS) is 2655.
On a daily basis, Shannon FIS observes traffic operating in Shannon FIR Class G airspace squawking A7000. This traffic often does not contact Shannon FIS for a service, nor is the controller aware if this traffic is monitoring the FIS frequency of 127.5MHZ.
Officially known as Frequency Monitoring Codes, a listening out squawk enables air traffic controllers to alert a pilot to their close proximity to the boundaries of controlled airspace - if their aircraft looks likely to infringe. Any aircraft fitted with a Mode A/C or Mode S transponder can use these codes. By entering the 2655 into the transponder and listening out on 127.5MHz, a pilot signifies to air traffic control that he/she is actively monitoring radio transmissions on that frequency and their aircraft position is visible on radar.
More details are available within the Integrated Aeronautical Information Package (IAIP).
NOTE: This initiative does not change any rules with regards to flight plans or pilot responsibilities with regards to airspace and rules of the air.