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FIS Langen tests Frequency Monitoring Code - New procedure to relieve FIS frequencies

Last updated on 15 March 2025
The overloading of flight information service (FIS) frequencies is a well-known problem in general aviation. Particularly in the spring and summer months, when the weather is ideal for VFR (Visual Flight Rules) flights, there is an increase in radio calls, meaning that pilots often have to wait a long time to log on or off the FIS. In order to make communication more efficient, FIS Langen is testing the Frequency Monitoring Code (FMC) procedure from 20 March to 26 October 2025. This method, which is already established in other European countries, enables VFR pilots to passively participate in FIS radio traffic without having to send a radio message to register.

What is the Frequency Monitoring Code (FMC)?

The FMC procedure allows pilots to monitor the FIS frequency without having to actively log in. By dialling in a special Transponder codes (3701) they signal to air traffic control that they are listening to the frequency and can be reached. This relieves the burden on radio traffic, as many VFR pilots only communicate with FIS for a short period of time anyway and do not require any further information.

The FMC test area is located west of Frankfurt (see AIP AIC 1/25) and does not overlap with military airspace such as Nörvenich, Büchel, Spangdahlem or Ramstein.

How does the Frequency Monitoring Code work?

To use the FMC procedure, pilots must follow the steps below:

  1. Frequency 123.525 MHz and check reception.
  2. Transponder code 3701 activate and Mode C or Mode S switch on.
  3. Always ready to listen on the FIS frequency.
  4. When leaving the frequency the transponder again 7000 (VFR standard code) set.

This allows the air traffic controllers in Langen to recognise which aircraft are in the FIS zone and listen to the radio. If necessary, the controller can make contact on their own initiative.

What are the advantages of the FMC process?

The main objective of the FMC test is to Reduction of unnecessary radio messages and the associated relief of the heavily frequented FIS frequencies. The most important advantages include

✔ Faster communication: Pilots do not have to actively register by radio, which reduces waiting times for a "free speaking slot".
✔ Increased efficiency for air traffic controllers: The workload of the FIS pilots is reduced so that they can concentrate on relevant enquiries.
✔ Better situation overview: The FIS controllers can immediately see on their displays which aircraft are listening to the frequency and can contact them directly if necessary.
✔ Flexibility for pilots: As the procedure is optional, pilots can decide for themselves whether they want to use the FMC or actively register with FIS as usual.

Special conditions for the test period

The test run of the frequency monitoring code is subject to certain restrictions:

  • The procedure applies only during the day, from 30 minutes before sunrise to 30 minutes after sunsetand only between 06:00 and 22:00 (local time).
  • It is exclusively for the Test area west of Frankfurt intended.
  • Military airspace (AoR) such as Nörvenich, Büchel, Spangdahlem and Ramstein are excluded.

How does FMC differ from other procedures?

Concepts similar to the Frequency Monitoring Code procedure already exist in several European countries:

  • Italy: The process is being used successfully there to relieve radio traffic.
  • Great Britain: There it is referred to as "Listening Squawk" and is an integral part of VFR aviation.

There is an important difference to the Transponder Mandatory Zones (TMZ) in Germany:

  • In a TMZ is the dialling in of the specific transponder code obligatory.
  • In the FMC test area is the utilisation voluntarybut recommended.

Important information for pilots

Although the FMC procedure improves the efficiency of the FIS service, the Responsibility for flight operations continues to be with the pilots. This means

  • FIS does not stagger traffic - the controllers only give directions to other aircraft if their workload permits this.
  • Collision avoidance remains the responsibility of the pilot.
  • Entry into airspaces subject to clearance: Listening to the FIS frequency does not replace the necessary clearance by the responsible air traffic control.

In addition, every pilot can contribute to improving radio discipline by precise and short radio messages used. Unnecessarily long dialogues - for example, repeatedly asking for information that has already been given - contribute to frequency overload.

Feedback from pilots welcome

DFS (German Air Traffic Control) calls on all pilots to use the Use FMC procedures as often as possible and give feedback. Feedback can be sent by e-mail to vfr@dfs.de be sent.

Conclusion

With the test of the Frequency Monitoring Codes DFS is taking an important step towards Optimisation of FIS communication in Germany. The overloading of FIS frequencies is to be reduced through the introduction of passive monitoring, which will benefit pilots and air traffic controllers alike.

If the FMC procedure proves successful, it could be extended to other regions in Germany in the future. Until then, it remains important for pilots to familiarise themselves with the procedures and actively test the system.

Here is the official AIP documentation: https://aip.dfs.de/BasicVFR/2025MAR06/chapter/02b0720172cb0ee0de46e008421e2784.html

Source references:
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