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Textbook application of a listening squawk allows early resolution of an infringement in a busy volume of airspace

As a measure to reduce the number and impact of airspace infringements, the CAA has introduced a series of Secondary Surveillance Radar (SSR) codes. There are 25 Frequency Monitoring Codes (FMCs) which are also known as listening squawks.

Listening squawks allow an Air Traffic Service Unit (ATSU) to be aware of aircraft that are on their frequency and enables the ATSU to quickly contact the pilot. In turn Air Traffic Control (ATC) can rapidly resolve infringements before they can become potentially more serious incidents. When controller capacity has allowed the pilot of an aircraft can be warned if it appears that it might infringe Controlled Airspace. Since their introduction many airspace infringements have been prevented by these warnings. On even more occasions, ATC has been able to rapidly resolve infringements before they became more serious. One such occurrence took place on 18 August 2019.

The pilot involved in the infringement plans all flights thoroughly, uses a moving map and has demonstrated an excellent approach to airmanship. The pilot reported having planned a local flight that had been flown many times and the plan incorporated the use of a moving map and Frequency Monitoring Codes (FMC).

The purpose of the flight was to fly a friend who had not flown in the aircraft type before. The passenger was excited about the flight and was asking lots of questions. Despite using a checklist, the pilot became distracted by the passenger and forget to set the correct QNH from that used during a previous flight. In addition, the pilot also failed to check the volume control on the iPad. After departure the pilot changed frequency to Farnborough LARS and set the FMC on his transponder. It was not until the Farnborough LARS controller transmitted his callsign, that he checked his iPad and, seeing a bright RED border, realised that he was too high in his current position and was infringing the Gatwick Control Area. On hearing his callsign the pilot immediately descended rapidly whilst apologising to the controller.

The LARS controller reports seeing and hearing the Airspace Infringement Alarm showing a 4572 (Farnborough LARS West FMC) infringing the Gatwick CTA with a MODE C indicating 1700 feet.

The controller called the aircraft using its callsign as seen on MODE S. The pilot answered straight away and said that he was following his moving map and remaining outside the Gatwick Control Zone. The pilot was asked to confirm his altitude on the London QNH of 1006 hPa. The pilot replied saying he was at 1600 feet on that QNH. The pilot was reminded that the base of controlled airspace in that location was 1500 feet and was asked to descend to 1400 feet to leave controlled airspace. The pilot replied that he was descending.

The pilot descended out of controlled airspace, apologised for the infringement and thanked the controller for assistance given.

The Infringement Coordination Group found that the pilot had followed the CAA’s advice to use a moving map and employing the use of a Frequency Monitoring Code (FMC) rather than squawking 7000 and not monitoring a frequency.

The pilot was open and honest in his report, stating that that despite thorough planning he had become distracted, by his passenger at the start of his flight. This led him to not setting the correct QNH which resulting in him flying higher than planned and flown. Distraction also played a played a part in his incorrect use of a moving map pre-flight and in-flight.

However, thanks to the effective use of a Frequency Monitoring Code (FMC), the infringement was quickly resolved with no requirement to apply safety intervention measures to Gatwick inbounds or departures. This textbook application of an FMC allowed the early resolution of an airspace infringement in a busy volume of airspace.

  • An Aeronautical Information Circular (AIC Y116/2019) was issued on 29 August 2019 outlining the use of FMC in the UK. This can be found on the NATS Aeronautical Information Service website at http://www.nats-uk.ead-it.com
  • A printable A5 card with the codes and associated frequencies is available to download: Listening squawks A5 card

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