Study Communication Failure

Study Communication Failure

52ND ANNUAL CONFERENCE, Bali, Indonesia, 24-28 April 2013

WP No. 87

Study Communication Failure

Presented by TOC

Summary

In regard to current work on ICAO Radio Communication Failure (RCF) procedures by the ICAO Communication Failure Coordinating Group (CFCG), TOC was tasked to study the subject. TOC has reviewed IFATCA Policy, proposes action in this working paper to develop a global unified procedure on RCF, and recommends Policy on the definition of RCF.

Introduction

1.1  Radio Communication Failure (RCF) in aviation is an eventuality that can result in undesirable and unsafe situations. This eventuality can be a communication failure in the ground system as well as a communication failure in the aircraft. This working paper is mainly addressing communication failure in the aircraft.

1.2  ICAO has published SARPs on how to respond in case of a communication failure. The SARPs on communication failure distinguish two different situations, communication failure in VMC or in IMC.

1.3. Due to differences in ATS and available ATM systems, the published ICAO SARPs for communication failure are not always adequate and practicable.

1.4 TOC was tasked to study the issue of RCF in collaboration with IFALPA, and possibly develop (additional) procedures for communication failure that are globally applicable.

Discussion

2.1 A complete loss of communication has become more rare due to plural and additional installation of communication equipment in modern aircraft and ATM systems. However, there are several areas, which could contribute commonly to a full or partial communication breakdown:

  • Airborne or ground radio equipment malfunction;
  • Sleeping receiver;
  • Stuck microphone.

2.1.1 Different levels of air services and differences in ATM systems require different solutions for communication failures. The phase of flight in which an RCF occurs often also influences the desired action. The air traffic density and complexity at some aerodromes could influence the decision to “land at nearest suitable aerodrome”.

2.1.2 According to ICAO SARPs a flight that is experiencing a communication failure should continue to destination according flight plan or last received ATC instructions. However, there could be several reasons for deviating from the original flight plan, and initiating an IFR turnback/diversion. Potential reasons for IFR turnback/diversion could be:

  • Critical (weather) situation en-route or at destination
  • Security requirements en-route or at destination
  • Required maintenance not available at destination
  • Emergency situation due to equipment failure, also resulting in communication failure
  • Landing at destination not possible due to unserviceable equipment on board and/or weather conditions

2.2 There is no ICAO definition on communication failure; therefore TOC decided it was necessary to draft a definition. It is very difficult to establish when or if a communication failure occurs without a definition on communication failure.

2.2.1  A communication failure can be a full breakdown or just a partial breakdown of the designated means of communication in a specific area. In example, means of communication could be a two-way radiotelephony communication or CPDLC.

2.2.2  According to TOC the definition of a communication failure should be:

A communication failure is a breakdown or unintentional downgrade in the designated means of air-ground communication required for ATS.


2.3 ICAO

2.3.1  ICAO has published SARPs and guidelines for communication failure.

2.3.2  ICAO Annex 2 Rules of the Air:

3.6.5.2 Communication failure. If a communication failure precludes compliance with 3.6.5.1, the aircraft shall comply with the voice communication failure procedures of Annex 10 Volume II, and with such of the following procedures as are appropriate. The aircraft shall attempt to establish communications with the appropriate air traffic control unit using all other available means. In addition, the aircraft, when forming part of the aerodrome traffic at a controlled aerodrome, shall keep a watch for such instructions as may be issued by visual signals.

3.6.5.2.1 If in visual meteorological conditions, the aircraft shall:

a) continue to fly in visual meteorological conditions; land at the nearest suitable aerodrome; and report its arrival by the most expeditious means to the appropriate air traffic services unit;

b) if considered advisable, complete an IFR flight in accordance with 3.6.5.2.2.

3.6.5.2.2 If in instrument meteorological conditions or when the pilot of an IFR flight considers it inadvisable to complete the flight in accordance with 3.6.5.2.1 a), the aircraft shall:

a) unless otherwise prescribed on the basis of regional air navigation agreement, in airspace where radar is not used in the provision of air traffic control, maintain the last assigned speed and level, or minimum flight altitude if higher, for a period of 20 minutes following the aircraft’s failure to report its position over a compulsory reporting point and thereafter adjust level and speed in accordance with the filed flight plan;

b) in airspace where radar is used in the provision of air traffic control, maintain the last assigned speed and level, or minimum flight altitude if higher, for a period of 7 minutes following:

1) the time the last assigned level or minimum flight altitude is reached; or

2) the time the transponder is set to Code 7600; or

3) the aircraft’s failure to report its position over a compulsory reporting point; whichever is later, and thereafter adjust level and speed in accordance with the filed flight plan;

c) when being radar vectored or having been directed by ATC to proceed offset using area navigation (RNAV) without a specified limit, rejoin the current flight plan route no later than the next significant point, taking into consideration the applicable minimum flight altitude;

d) proceed according to the current flight plan route to the appropriate designated navigation aid or fix serving the destination aerodrome and, when required to ensure compliance with e) below, hold over this aid or fix until commencement of descent;

e) commence descent from the navigation aid or fix specified in d) at, or as close as possible to, the expected approach time last received and acknowledged; or, if no expected approach time has been received and acknowledged, at, or as close as possible to, the estimated time of arrival resulting from the current flight plan;

f) complete a normal instrument approach procedure as specified for the designated navigation aid or fix; and

g) land, if possible, within 30 minutes after the estimated time of arrival specified in e) or the last acknowledged expected approach time, whichever is later.

ICAO Doc 4444 PANS/ATM:

6.3.2.5.2 Where clearances for departing aircraft containing no time or geographical limit for an initial or intermediate level are utilized, action to be taken by an aircraft experiencing air-ground communication failure in the event the aircraft has been radar vectored away from the route specified in its current flight plan should be prescribed on the basis of a regional air navigation agreement and included in the SID description or published in AIPs.

8.8.3.1 AIRCRAFT RADIO TRANSMITTER FAILURE

8.8.3.1.1 1 If two-way communication is lost with an aircraft, the controller should determine whether or not the aircraft’s receiver is functioning by instructing the aircraft on the channel so far used to acknowledge by making a specified manoeuvre and by observing the aircraft’s track, or by instructing the aircraft to operate IDENT or to make SSR code and/or ADS-B transmission changes.

Note 1. – Transponder-equipped aircraft experiencing radiocommunication failure will operate the transponder on Mode A Code 7600.

Note 2. – ADS-B-equipped aircraft experiencing radiocommunication failure may transmit the appropriate ADS-B emergency and/or urgency mode.

8.8.3.1.2 If the action prescribed in 8.8.3.1.1 is unsuccessful, it shall be repeated on any other available channel on which it is believed that the aircraft might be listening.

8.8.3.1.3 In both the cases covered by 8.8.3.1.1 and 8.8.3.1.2, any manoeuvring instructions shall be such that the aircraft would regain its current cleared track after having complied with the instructions received.

8.8.3.1.4 Where it has been established by the action in 8.8.3.1.1 that the aircraft’s radio receiver is functioning, continued control can be effected using SSR code/ADS-B transmission changes or IDENT transmissions to obtain acknowledgement of clearances issued to the aircraft.

8.8.3.2 COMPLETE AIRCRAFT COMMUNICATION FAILURE

When a controlled aircraft experiencing complete communication failure is operating or expected to operate in an area and at flight levels where an ATS surveillance service is applied, separation specified in 8.7.3 may continue to be used. However, if the aircraft experiencing the communication failure is not identified, separation shall be applied between identified aircraft and all unidentified aircraft observed along the expected route of the aircraft with the communication failure, until such time as it is known, or can safely be assumed, that the aircraft with radiocommunication failure has passed through the airspace concerned, has landed, or has proceeded elsewhere.

8.8.6.1 In the event of complete failure of the ground radio equipment used for control, the controller shall, unless able to continue to provide the ATS surveillance service by means of other available communication channels, proceed as follows:

a) without delay inform all adjacent control positions or ATC units, as applicable, of the failure;

b) apprise such positions or units of the current traffic situation;

c) request their assistance, in respect of aircraft which may establish communications with those positions or units, in establishing and maintaining separation between such aircraft; and

d) instruct adjacent control positions or ATC units to hold or re-route all controlled flights outside the area of responsibility of the position or ATC unit that has experienced the failure until such time that the provision of normal services can be resumed.

2.3.3 ICAO Annex 10 Volume 2 Aeronautical Telecommunications lists additional provisions on RCF.

2.4 ICAO provisions on RCF are extensive, but appear not always to be practicable.

2.4.1 Annex 2 Rules of the Air paragraph 3.6.5.2.2:

“unless otherwise prescribed on the basis of regional air navigation agreement, in airspace where radar is not used in the provision of air traffic control, maintain the last assigned speed and level…”

This means pilots should always be aware of procedures for communication failure in regional air navigation agreements of every part of the route they fly in. This is not always practicable.

2.4.2 ICAO has established a Communication Failure Coordinating Group (CFCG) to review provisions on RCF. IFATCA has a representative, Jonathan Daoust (CATCA), in this group. Jonathan attended the meeting of this group in October 2012 in Montreal, and is working close together with TOC to represent IFATCA’s opinion on the issue.

2.5 IFATCA Policy is:

There is one unified global procedure for RTF failure.

 

2.5.1  IFATCA Policy is mentioning Radiotelephony (RTF) failure, ICAO is presently using the term Radio Communication Failure (RCF), and therefore this paper will continue to use RCF. TOC reviewed the Policy on RCF in 2006. One of the conclusions out of that working paper was the fact that information relating to RCF is contained in different documents in different forms. This highlighted the need for a simplified approach in producing a unified global procedure.

2.5.2  In recent years RCF has become more prevalent in the form of Prolonged Loss Of Communication (PLOC). This term has come into use in civil aviation to describe a phenomenon that not only covers technical communication failure, but also mis- management of the man-machine interface. For security reasons (e.g. terrorist attacks), any aircraft silence lasting more than a few minutes is often treated as a potential risk. The number of interceptions by military aircraft due to PLOC has increased substantially over the last years.

2.5.3  IFATCA Policy on RCF should be amended in regard to the used means of communication. Due to technical issues, radiotelephony is not always available for communication. The use of data-link communications is already in place in several locations (oceanic- and remote controlled airspace), and is expected to increase in due time. Therefore the term “RTF failure” in IFATCA Policy on RCF should be amended to “communication failure” to cover future developments in air to ground communication.


2.6 IFALPA

2.6.1  IFALPA believes that neither the current nor the proposed provisions fully reflect the realities of the present day operational environment and the operational needs in extreme rare events. IFALPA is participating in the ICAO Communication Failure Coordinating Group.

2.6.2  IFALPA believes that ICAO should develop a global solution for IFR Turnback Contingency Procedures based on safety management principles. According to IFALPA there could be several options for RCF:

Option 1

When the pilot in command considers it advisable for safety, taking into account, inter alia, the complexity of the operating environment, an aircraft flying shall:

a)  select code 7601 and transmit IDENT at least twice in two minutes. And if practicable, proceed according to the current flight plan for two minutes.

b)  land at the nearest suitable aerodrome; and

c)  report its arrival by the most expeditious means to the appropriate ATS-unit.

Option 2

When experiencing a communication failure, pilots should select code 7600 and keep it for at least 10 minutes. If the pilots need to deviate from the basic ICAO IFR procedure (i.e. to continue to the destination in accordance with the filed flight plan) then codes 7601 – 7607 might be used to indicate the proposed course of action. Example: 7601 for continuation in VFR; 7602 for return to departure aerodrome with a left turn; 7603 for return to departure aerodrome with a right turn; 7604 to indicate fuel dumping; etc.

Note: transponder codes 7601 to 7607 need not be reserved all the times. The option to squawk 7600 for 10minutes, would give ATC time to reassign codes to aircraft in the 7601 – 7607 range and make these codes available to indicate aircraft intentions.

Option 3

Same as option 1, except code 7700 should be used when the standard IFR procedure is not followed. This option is not preferred for a number of reasons, such as the ICAO definition of Emergency, and the potential for loosing a possibility to indicate the change of situation to a real emergency.


2.7 Local RCF procedures

2.7.1 States publish in AIPs what action is expected by aircraft with a communication failure. Sometimes these procedures are slightly different from ICAO SARPs. An example from AIP The Netherlands:

3 COMMUNICATION FAILURE

3.1 General procedures for IFR flights

3.1.1 Flying in IMC

Pilots of an IFR flight in IMC, or not able to comply with paragraph 3.1.2, shall:

  • select code 7600.
  • in case of radar vectoring, proceed as directly as possible to the route specified in the current flight plan (1)
  • maintain for a period of 7 minutes (2) the last assigned speed and level, or minimum flight altitude if this is higher. The period of 7 minutes commences at the time the transponder is set to code 7600 (contrary to ICAO SUPPS- Doc 7030/4 para 5.3.1 b).
  • subsequently adjust speed and level as specified in the filed flight plan (3).

(1)  With regard to the route to be flown, the current flight plan (including subsequent changes) will be used.

(2)  The period of 7 minutes is to allow the necessary air traffic control and co-ordination measures.

(3)  With regard to levels and speed, the filed flight plan (as initially filed by the pilot) will be used.

3.1.2 Flying in VMC

The pilot of an IFR flight in VMC shall:

  • select transponder code 7600.
  • continue to fly in VMC.
  • land at the nearest suitable aerodrome; and
  • report its arrival time by the most expeditious means to the appropriate ATS unit.

3.2 Arriving flights

For IFR flights with a destination situated in the Amsterdam FIR, communication failure procedures are contained in the paragraph ‘Instrument Approach Procedures’ for each airport (AD 2.22).

2.7.1.1 As mentioned in paragraph 3.2 of the AIP The Netherlands, there are different communication failure procedures for each airport in the Amsterdam FIR. These differences also result in additional complexity to deal with a communication failure.

2.7.2 Publications, like in the AIP The Netherlands, imply that pilots are expected to be aware of all regional procedures for communication failure for every part of the route. There are differences in RCF procedures that often concern the approach phase, which is a critical phase in the flight where there is usually not much time to confirm and handle according local RCF procedures. Practically pilots will not always have the local procedures for RCF at hand, and it will normally take some time for the crew to acquire the correct local RCF procedures.


2.8 RCF in VMC

2.8.1  ICAO prescribes in Annex 2 Rules of the Air that aircraft with communication failure in visual meteorological conditions shall “land at the nearest suitable aerodrome”, or “if considered advisable, complete an IFR flight in accordance with 3.6.5.2.2”. This is not always easy to determine. ICAO does not explain what should be considered as a suitable aerodrome, so it is up to the flight crew to determine what the criteria for the nearest suitable aerodrome would be. Furthermore, it could be very difficult for the responsible ATC-unit to determine the intention of the pilots.

2.8.2  The decision to continue to fly in VMC could result in ending up in IMC in a later phase of the flight. Which at that moment could result in a complex situation for the pilots, as there would probably be no standard way of continuing IFR from that moment on.

2.8.3  Present air traffic density often does not easily facilitate aircraft with communication failure to join a visual circuit without interfering with other aerodrome traffic. And what if multiple aircraft are confronted with a communication failure due to ground radio equipment failure or a sticking microphone?

2.8.4  ICAO prescribes that aircraft, “if considered advisable”, should complete the flight as in instrument meteorological conditions as mentioned in Annex 2 paragraph 3.6.5.2.2.

2.8.4.1 “If considered advisable” can be interpreted in multiple ways. Pilots are not always aware of the traffic situation around an aerodrome. And ICAO does not state or explain what exactly “if considered advisable” means.


2.9 Other means of communication

2.9.1  Most commercial aircraft are equipped with more than one means of communication like additional VHF, HF, Satcom, CPDLC, ACARS, cell-phone, etc. According to ICAO Annex 2, aircraft should attempt to establish communications with the appropriate air traffic control unit using all other available means. In the opinion of TOC, ICAO should more emphasize this option. First establishing contact with ATC and inform them about the intentions in regard to the communication failure, could prevent uncertainty and misunderstanding. The available equipment on ground should also be taken into consideration.

2.9.2  In the opinion of TOC, for a unified procedure for RCF, flight crews should have access to dedicated telephone numbers and/or CPDLC-codes for every State or FIR. These telephone numbers and/or CPDLC-codes could be used in case of a communication failure. The dedicated telephone numbers should be attended 24/7, and able to dispatch the pilots to the responsible ATS-unit or another unit that can coordinate the situation with the responsible ATS-unit.


2.10 Diagram to use with RCF

2.10.1 Due to the variety of different situations, in which a communication failure could occur, there is no one solution for the problem. TOC suggests developing a sort of diagram that pilots can use to establish the best solution in a particular situation. The diagram could be used as a follow up, when contacting ATC by other means of communication fails. For clarification TOC has drafted an example of a possible diagram for RCF.

2.10.2  This diagram is not yet complete, and should be further developed, possibly in corporation with all stakeholders in the ICAO CFCG. Considering developments with tablets on the flight deck, this diagram could also be incorporated in software, completed with ICAO and local provisions for RCF. An application developed for use with a tablet could enable pilots to quickly determine the proposed action for RCF. By entering the position of the aircraft in the tablet application, relevant telephone numbers and CPDLC codes and ICAO and/or local RCF procedures should easily and quickly be obtained by the flight deck.

2.10.3  If it is unknown to the pilots if the aircraft is in a radar/surveillance environment, the pilots should execute the procedure for the non-radar/surveillance environment and additionally transmit the transponder code concerning their intentions. It would be advisable for pilots always to set the concerning transponder code, also in a non- radar/surveillance environment, because there could be other stations that could relay their intentions to the responsible ATS-unit. However, it must be considered that using transponder codes for RCF in an ADS-B environment could result in problems with ATM-systems.

Conclusions

3.1  Although radio communication failures are becoming more rare, they still result in undesirable and unsafe situations. Due to differences in the provision of Air Traffic Services (i.e. radar and non-radar), and local situations and environment (i.e. terrain, traffic situation, populated areas, etc.), ICAO prescribed procedures are not always adequate and practicable.

3.2  To address the problem, first a definition of the issue is required. A definition for communication failure to cover future developments in air-ground communication for ATS is recommended for acceptance.

3.3  Radio communication is not always the primary designated means for communication. In oceanic- and remote airspace CPDLC is sometimes the primary designated means for communication. The use of CPDLC is expected to increase in the near future, also in high-density traffic areas, to reduce the congestion of voice communication.

3.4  Due to various reasons continuing according to flight plan or by last received ATC instructions is not always practicable when experiencing a communication failure. Although desirable, one global unified procedure for RCF will be difficult to establish due to the differences in situations where a communication failure could occur. Therefore TOC suggest a diagram that should be used as a global unified procedure to determine the best solution for every different situation. The ICAO Communication Failure Coordinating Group (CFCG) would be the appropriate institution to develop such a diagram.

Recommendations

It is recommended that;

4.1  IFATCA Policy is:

The definition of a communication failure is:

A communication failure is a breakdown or unintentional downgrade in the designated means of air-ground communication required for ATS.

And is included in the IFATCA Technical and Professional Manual.

4.2  IFATCA Policy:

There is one unified global procedure for RTF failure.

is amended to read:

There is one unified global procedure for communication failure.

And is included in the IFATCA Technical and Professional Manual.

References

ICAO Annex 2 Rules of the Air.

ICAO Annex 10 Aeronautical Telecommunications.

ICAO Doc 4444 PANS/ATM.

IFALPA ATS Committee.

AIP The Netherlands.

www.skybrary.aero

Last Update: September 30, 2020  

April 22, 2020   431   Jean-Francois Lepage    2013    

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