Listen On: How the Map Predicts a Frequency

Summary: How the aircraft panel decides which frequency an aircraft is most likely working, what the confidence badge means, and how the live feed changes the answer.

The Listen on block at the top of every aircraft’s info panel is the map’s best answer to “what do I tune”. It is a prediction, worked out from where the aircraft is, what it is doing and what it is squawking, and then checked against what the live UKAFG feed has actually heard. This article explains how that answer is reached so you can judge it.

The ladder

The map tries a list of rules in order and the first that applies gives the answer. In outline:

1. Not an aircraft — tower transponders, airport vehicles and obstacles on the feed get no frequency.
2. Emergency — a crew declares an emergency on the frequency it is already working and stays there, with the controller who already has it; Guard is the fallback if contact is lost, or for a relay. So the map works out the working frequency exactly as it would without the emergency and headlines that, marked emergency declared here, with Guard (121.5, or UHF 243.0 for a military aircraft) as the first alternative. With a radio-failure squawk (7600) the working frequency still leads, and the note says blind calls may come on Guard too.
3. Outside UK airspace — beyond the London and Scottish FIRs the map says so rather than guess; over the Atlantic it notes Shanwick is HF and datalink.
4. The airfield the aircraft is at — inside a CTR, ATZ or MATZ, or on the ground or just departed from its departure field, or on approach to its arrival field, the airfield’s own frequencies are ranked by what listeners actually hear there. The map carries a profile of every major base built from real scanner logs: which frequency is heard for which phase of flight and type of aircraft. So a Typhoon on approach to Coningsby is put on the Approach ICF and a Tutor on final at Cranwell on the tower, and the reason line says heard 19% of the time here. Bases the scanners never hear use the pattern across all bases; civil airports use the usual handover order. NATO Common, ATIS and Havequick channels are never headlined.
5. On the ground with no airfield known — says so.
6. Refuelling — a tanker inside a refuelling area, or an aircraft the map has seen join up with one, gets the towline.
7. Formation or training area — a military aircraft in formation or inside a training area gets its squadron’s air-to-air. A named flight with no squadron number is matched by its name instead: the BBMF gets its own 122.065, used in formation, and never the station’s fast-jet ops. An aircraft heard but not placed while a formation mate is on the map (KING33 beside KING31 and KING32) is placed beside that mate, so it gets a prediction too.
8. Swanwick Mil sector — a military aircraft in the open FIR gets the initial contact frequency of the Swanwick Mil sector it is inside, UHF preferred, unless it is inside controlled airspace or squawking a civil transit code, when the civil controller has it.
9. The squawk — a code that names a unit and a frequency, close enough to trust.
10. The en-route sector — the civil sector the aircraft is inside, confirmed against the nearest transmitter of that sector’s frequencies. A sector known to be normally worked on a neighbour’s frequency (Rathlin East on Rathlin West’s 129.1, for example) is headlined on that frequency with its own as the alternative.
11. A CTA or TMA’s own frequencies, then a CCAMS code with nothing resolved, then the Flight Information Service for the latitude.

What the live feed adds

Before the answer is shown, the map asks the live UKAFG feed about every frequency it considered, over the whole day. Then it decides again with that in hand: a towline, a squadron’s air-to-air or ops list, or a sector’s VHF/UHF pair comes out with the frequency heard in the last 15 minutes first, then the one heard today, then the published order, and at an airfield a frequency heard in the last 15 minutes goes above anything the long-run profile says. The reason line says so: heard 4 min ago, heard 3 times today. If the headline itself was heard today, a chip says how long ago; if another likely frequency was heard more recently, it takes the headline’s place. The feed only knows what members’ scanners have reported, so a frequency nobody was monitoring falls back to the published order.

The confidence badge

• Certain — the frequency was heard on the live feed within the last minute or two.
• High — the data points one way: the squawk agrees with the sector, the transmitter check agrees, the airfield’s profile is clear, or the feed heard it minutes ago.
• Medium — a good guess with a real alternative; look at Also try.
• Low — little to go on.

Also try

The next best two, each with a word on why: the other band of a pair, the frequency the sectors use when split, the departures or air-to-air frequency heard second most often. Between them and the headline you will usually hear the aircraft.

What it cannot know

Handovers near sector boundaries happen a little before or after the line on the map; controllers combine and split sectors through the day; a squadron may be on a discrete frequency nobody has listed; and military aircraft on the ground are often on a frequency the map cannot see. If you hear an aircraft somewhere the map did not suggest, the feedback link on the panel is the quickest way to tell us, and reports like these are how the sector notes and the airfield profiles improve.