24TH ANNUAL CONFERENCE, Athens, Greece, 18-22 March 1985
WP No. 51
Review of Lateral and Longitudinal Separation
At IFATCA 83, Committee B discussed WP 57/83, presented by New Zealand. SC 1 produced WP 61/84 in Estoril and an additional paper WP 95/84. This last paper introduced Longitudinal separation into what had previously been a review of Lateral Separation.
The specific ICAO separation standards under review are published in PANS/RAC 4444, Page 3.5, and 3.8.
During SC 1 discussions, it has been made evident that both SC 1 practice and the Executive Board policy is to review concepts rather than values in separation.
WP 62/84 was adopted in Estoril, as guidance material. Para 4.2 of that paper indicated that SC 1 should move to develop policy on lateral track separation.
Additional input throughout the year has been made by the South African and New Zealand associations.
Para 2 of WP 61/84 outlined the areas of concern to IFATCA. Some of these areas seem suitable for the formation of policy by IFATCA. In particular the following:
a) Non promulgation of lateral distance to be achieved – and consideration of the Buffer zone tolerances and how they should be applied, i.e. the minimum lateral distance to be achieved must not be diminished by tolerances of the Buffer-zone;
b) the reduction of lateral separation distances below that of radar control minima;
c) ICAO does not specify that the controllers requires the aircraft to be established on track as part of the method of achieving the separation.
In respect of the Regional Oceanic Longitudinal separations on crossing tracks mentioned in WP 95/84, it highlights many of the problems of procedural separation standards. Where separation is stated in time along a track, and both aircraft are slow, the physical separation between aircraft can be quite small. When aircraft are not required to amend estimates that are less than 3 minutes in error, these physical distances can further decrease. To then allow (in this regional example) for aircraft to deviate from track by a considerable distance for weather avoidance without telling ATC, in addition to normal navigation tolerances, can lead to the total loss of separation. Two elements can be picked out from this paper for amendment where any crossing track separation lateral or longitudinal is stated. If aircraft are to be permitted to route off-track, then it is essential that ATC be informed. Alternatively, where a regional procedure allows track deviation, regional separation should be increased to take account of the requirement.
In respect of the various problems it is possible for IFATCA to consider policy on some of the items of concern stated in WP61/84. These should be in addition to existing policy statements B.3 of 67 and B$ of 69 as amended by B10 of 78.
It is recommended that:
IFATCA has grave reservations concerning the application and interpretation of horizontal non- radar separation as detailed in ICAO PANS-RAC Doc 4444. Of particular concern are those minima laid down for track separation and for aircraft on crossing tracks. In studying these minima IFATCA is of the opinion that the separation values should be re-examined. Therefore, IFATCA requests ICAO to undertake an urgent review of non-radar separation minima and to take steps to ensure that such minima are unambiguous .
Last Update: September 20, 2020