RTF Frequency Jamming

RTF Frequency Jamming

23RD ANNUAL CONFERENCE, Estoril, Portugal, 26-30 March 1984

WP No. 58

RTF Frequency Jamming


This subject was first raised at IFATCA 76. Consideration at succeeding conferences led to the formulation of IFATCA’s present policy on the subject (Appendix A, para’s 1(c) and 2.5), recommending the development of a technical solution to the problems.

At IFATCA 83, during discussions of SC 1’s report on IFALPA ATS Study Group activities, the IFALPA observer expressed his Federation’s continuing concern about the problem and the lack of progress towards implementation of a technical solution. Following further committee discussion Conference charged SC 1 with reviewing IFATCA’s existing policy and with reconsidering practical technical solutions and implementation aspects.

Historical Background


The subject was first raised in a short working paper presented by the Swiss Association. SC 1 were charged with investigating and reporting back.


After discussion of SC 1’s paper Conference recognised that a technical solution was desirable, but tasked SC1 also with looking into the feasibility of a procedural solution, based on information to be provided by MA’s.


Although considerable interest had been shown by MA’s at IFATCA 77 no inputs were subsequently received by SC 1 and so no proposals were put forward for consideration. Conference tasked SC 1 and MA’s with completing the job for IFATCA 79.


Again no inputs were received by SC1 from MA’s, but the European Association submitted a Working Paper proposing a procedural solution based on the use of the International Distress frequency 121.5 as a “guard frequency”. Following lively discussion this proposal was referred to SC 1 for more detailed consideration.


After discussion of SC 1’s Working Paper Conference decided that the 121.5 based procedural solution would not be practicable for world-wide application. Following a proposal by The Netherlands association that a technical solution providing the pilot with “Transmitter-on “ warning indications was the best practicable solution to the problem of frequency jamming, a policy statement to this effect was agreed (See Appendix A, Paras 1 (c) and 2.5). this complete IFATCA action on the subject and the policy statement is still in force.

Progress Towards Implementation of a Technical Solution

Until very recently there has been no evidence of any great interest shown by Equipment Manufacturers or airline Operators in the development and implementation of a technical cockpit based solution to frequency jamming – which still remains a very real problem for both pilots and controllers.

During the year SC 1 has discussed possible simple methods of providing such a technical solution and IFALPA have been moving in the same general direction, though one of their concerns is to ensure that any warning system provided for pilots shall be acceptable to them vis à vis the many other warning devices installed in the cockpit for other purposes.

Shortly before completion of this years WP, SC 1 were informed by the Eurocontrol Association of an operational trial to be conducted in the near future by KLM of a simple (patent-pending) device, the “CONTRAN-UNIT” (CONflict TRANsmissions – UNIntentional Transmissions), designed not only to warn the pilot of unintentional transmissions but also to inhibit transmissions on RTF Channels already occupied, so preventing simultaneous transmissions. KLM have promised to provide the Eurocontrol Association with a copy of their report on the device after completion of its evaluation over a period of 3 Months in one of the airlines DC9-30 aircraft.

To Conclude

Existing IFATCA Policy on Frequency Jamming (Appendix A, Para’s 1c and 2.5) is still valid. IFATCA should confirm that :

  1. Frequency jamming remains a very real operational problem;
  2. That no procedural solution acceptable for world-wide application is practicable;
  3. That a technical solution on the flight deck should continue to be sought, but that such a solution must be acceptable to both pilots and airline operators.

IFATCA should express concern at the apparent general lack of interest in, and progress towards, the development and implementation of a cockpit-based technical solution by industry and aircraft operators. IFATCA should, however , welcome the initiative taken by KLM to evaluate the simple “CONTRAN-UNIT” device, the inclusion in which of protection against simultaneous transmissions, though not identified by ATC as a significant operational problem, will provide a useful ‘bonus’.

It is recommended that:

The IFATCA objective is to achieve reduction in workload in the air and on the ground by the development of simple, clear and standard R/T communications Failure Procedures readily available to pilots and controllers which provide :

  1. In a standard form, indication of the action to be taken by pilots in any particular phase of flight or any particular airspace, if R/T communications failure occurs;
  2. A reliable basis upon which controllers can provide uninterrupted ATC service to those aircraft retaining R/T communications with the ground in a safe , orderly and expeditious manner, without impairing the freedom of action of the pilot experiencing R/T failure; and
  3. Freedom from interference by inadvertent aircraft transmissions which cause temporary, but total, loss of R/T communications between air and ground to all other aircraft on the R/T channel affected.

And that:

The basic procedures for adoption in the event of radio communication failure contained in Annex 2.10 and 11 and PANS RAC be collated and issued in a single ICAO Document in a form suitable for access by pilots and controllers.

The supplementary procedures contained in States A.I.P. be simplified, standardised and (where practicable) illustrated.

The existing ICAO basic procedure be extended to include action to be taken by radio-equipped IFR flights being conducted outside controlled airspace.

States be encouraged to make the maximum use of both primary radar and SSR, not only to assist pilots with R/T Failure, but also to minimise the penalties which may otherwise be imposed on other traffic.

A visual/audio warning be included in the specification for aircraft radio transmitters to indicate to pilots when transmission is actually taking place.

Last Update: September 20, 2020  

November 30, 2019   235   Jean-Francois Lepage    1984    

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