The IATA calls them "In-Flight Broadcast Procedures" or IFBP. The ICAO calls them Traffic Information Broadcasts by Aircraft" or TIBA. As pilots we've known them as "Broadcast in the Blind."
Whatever you call them, they used to be the staple of remote flight operations in places like Africa, South America, India, and parts of Australia. There aren't many TIBA regions left but you still find them. So if you find a note on the chart calling for TIBA or IFBP, you should know this.
So what's it all about?
Of course all that is theory and you hope those deconflicting flight plans have done a good job. All this was really terrifying about twenty years ago. (In some parts of the world they didn't even make the pretense of speaking English.) Now your biggest fear is that they don't have TCAS or for some reason have it turned off.
Everything here is from the references shown below, with a few comments in an alternate color.
[ICAO Annex 11 Attachment B, para;1]
1.1 Traffic information broadcasts by aircraft are intended to permit reports and relevant supplementary information of an advisory nature to be transmitted by pilots on a designated VHF radiotelephone (RTF) frequency for the information of pilots of other aircraft in the vicinity.
1.2 TIBAs should be introduced only when necessary and as a temporary measure.
1.3 The broadcast procedures should be applied in designated airspace where:
1.4 Such airspaces should be identified by the States responsible for provision of air traffic services within these airspaces, if necessary with the assistance of the appropriate ICAO Regional Office(s), and duly promulgated in aeronautical information publications or NOTAM, together with the VHF RTF frequency, the message formats and the procedures to be used. Where, in the case of 1.3 a), more than one State is involved, the airspace should be designated on the basis of regional air navigation agreements and promulgated in Doc 7030.
1.5 When establishing a designated airspace, dates for the review of its applicability at intervals not exceeding 12 months should be agreed by the appropriate ATS authority(ies).
[ICAO Annex 11 Attachment B, para;2]
2.1 VHF RTF frequency to be used
2.1.1 The VHF RTF frequency to be used should be determined and promulgated on a regional basis. However, in the case of temporary disruption occurring in controlled airspace, the States responsible may promulgate, as the VHF RTF frequency to be used within the limits of that airspace, a frequency used normally for the provision of air traffic control service within that airspace.
2.1.2 Where VHF is used for air-ground communications with ATS and an aircraft has only two serviceable VHF sets, one should be tuned to the appropriate ATS frequency and the other to the TIBA frequency.
2.2 Listening watch
A listening watch should be maintained on the TIBA frequency 10 minutes before entering the designated airspace until leaving this airspace. For an aircraft taking off from an aerodrome located within the lateral limits of the designated airspace listening watch should start as soon as appropriate after take-off and be maintained until leaving the airspace.
2.3 Time of broadcasts
A broadcast should be made:
2.4 Forms of broadcast
2.4.1 The broadcasts other than those indicating changes in flight level, i.e. the broadcasts referred to in 2.3 a), b), c), d) and g), should be in the following form:
2.4.2 Before a change in flight level, the broadcast (referred to in 2.3 e)) should be in the following form:
2.4.4 Broadcasts reporting a temporary flight level change to avoid an imminent collision risk should be in the following form:
2.5 Acknowledgement of the broadcasts
The broadcasts should not be acknowledged unless a potential collision risk is perceived.
[ICAO Annex 11 Attachment B, para;3]
3.1 Changes of cruising level
3.1.1 Cruising level changes should not be made within the designated airspace, unless considered necessary by pilots to avoid traffic conflicts, for weather avoidance or for other valid operational reasons.
3.1.2 When cruising level changes are unavoidable, all available aircraft lighting which would improve the visual detection of the aircraft should be displayed while changing levels.
3.2 Collision avoidance
If, on receipt of a traffic information broadcast from another aircraft, a pilot decides that immediate action is necessary to avoid an imminent collision risk, and this cannot be achieved in accordance with the right-of-way provisions of Annex 2, the pilot should:
3.3 Normal position reporting procedures
Normal position reporting procedures should be continued at all times, regardless of any action taken to initiate or acknowledge a traffic information broadcast.
ICAO Annex 11 - Air Traffic Services, International Standards, Annex 11 to the Convention on International Civil Aviation, Fifteenth Edition, July 2018
Jeppesen Airway Manual
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