ATC859

An open, honest and useful report where there was perhaps some expectation bias as well as a classic case of a misheard/misinterpreted instruction. We have checks and balances in place in aviation to try and mitigate these errors; a readback of ATC instructions for example before enacting them, particularly if there is a change in what is expected or previously instructed. ATC readback is a good habit to adopt, even if it’s not an actual requirement at that airfield.

Although it’s not specifically pertinent to what happened to this reporter, we felt that it might be useful and timely to provide a reminder about the different levels of service that can be found at airfields. CHIRP often receives information about incidents where pilots mistakenly interpret advisory calls as instructions or vice versa so we take every opportunity to refresh the different services provided by ATCO, AFIS and A/G – the following is courtesy of CAA Safety Sense Leaflet 22 – Radiotelephony (https://www.caa.co.uk/our-work/publications/documents/content/safety-sense-leaflet-22/).

Air Traffic Control Service

An Air Traffic Control Service (ATCS) can only be provided by Air Traffic Control Officers (ATCO).

ATCO may issue clearances and instructions to aircraft on the ground and in the air, within the applicable area of operation. Within the aerodrome air traffic zone (ATZ) or controlled airspace (CAS), compliance with ATC instructions is mandatory. ATC services at an aerodrome will often be split between an approach control service (callsign ‘Approach’ or ‘Radar’) and an Aerodrome Control Service (callsign ‘Tower’). Where both services are in operation, an approach controller will be your first point of contact, and they will pass you over to ‘Tower’ as you get closer to the aerodrome. Larger aerodromes may also have a ground control frequency (callsign ‘Ground’).

Aerodrome Flight Information Service

An Aerodrome Flight Information Service (AFIS) can be identified by the callsign suffix ‘Information’.

AFIS provides information to pilots for the conduct of their flight at an aerodrome and within the associated ATZ. In the UK, an AFIS is permitted to issue mandatory instructions to aircraft on the ground up until the aircraft passes a runway holding point. Note this is a UK difference from ICAO, in most states AFIS does not issue instructions at all. AFIS units do not issue instructions to aircraft in the air, however they may request position reports that are consistent with the aerodrome’s published traffic procedures. An AFIS unit will usually pass information about known traffic in the vicinity of the aerodrome, although this should be treated as advisory only.

Air/Ground Communication Service

AGCS stations can be identified by the callsign suffix ‘Radio’.

Air/Ground Communication Service (AGCS) is the most basic form of aeronautical ground station you will encounter at an aerodrome. Provision of AGCS does not have formal status as an air traffic service. The operator of an AGCS may provide traffic and weather information to pilots operating on and in the vicinity of the aerodrome. Traffic information is normally based on reports from other pilots. It is not a requirement for an AGCS operator to have a continuous view of the ATZ environment or movement area, so such information may not be complete or accurate. The radio operator has no power to issue clearances or instruct aircraft either in the air or on the ground. While information provided by the radio operator may be used to assist a pilot in making a decision, the safe conduct of the flight remains the pilot’s responsibility. When operating in the AGCS environment, the basic principle is that aircraft announce their position and separate themselves from other aircraft in accordance with the Rules of the Air and any published aerodrome procedures. Only carry out a manoeuvre (such as taxiing, take-off or landing) if you are satisfied that it is safe to do so and that it will not bring you into conflict with other traffic.

Unattended Aerodrome SAFETYCOM

Unattended Aerodrome SAFETYCOM is a common traffic advisory frequency for use at aerodromes that do not have an assigned frequency. It is currently 135.480 MHz and may be used within 10 NM and up to 1000 ft above the height of the traffic circuit at an aerodrome. Aircraft should announce their position and intentions at the normal points using the callsign “Traffic” after stating the name of the aerodrome they are operating at. Repeating the name of the aerodrome at the end of the transmission further mitigates the risk of confusion when aerodromes are in proximity to each other. Some UK aerodromes allow aircraft movements to take place outside the hours during which an air traffic service or AGCS is normally provided. In this case pilots should commence transmissions with “[aerodrome name] Traffic” on the allocated frequency for that aerodrome.