23RD ANNUAL CONFERENCE, Estoril, Portugal, 26-30 March 1984
WP No. 95
Longitudinal Separation Anomalous Interpretations
This late paper is introduced as the author feels that the anomalous interpretation of PANS/RAC Doc 4444 has a bearing on WP No 61. It may be helpful to delegates to consider the implications of this paper in parallel with WP 61.
The anomalous interpretation of Doc 4444 discussed in this paper is a recent occurrence in New Zealand and it is stressed that it is the subject of urgent correspondence and consultation at the moment.
Recently , following a minor incident, it became apparent that the wording of the longitudinal separation (crossing tracks) in the NZ Manual of ATS may have been misinterpreted. A clearer wording was sought.
NZMST (CAD) Head Office issued a signalled amendment to NZMATS changing one word in the wording. The change from the word “from” to “at” has in effect actually halved the minima and when allowable navigation errors and worst case allowable track deviation is taken into account, in Oceanic airspace, the aircraft can be very much closer than the standard 100nm.
The amendment has been challenged but the justification was quoted as the criteria laid down in Doc 4444. On inspection it can be seen that the relevant paragraph is over-simplified, the explanation sparse and the diagrams misleading.
The matter continues to be debated at a national level and NZ controllers will continue to apply the safe interpretation of the original wording until the matter is satisfactorily resolved. However, if there can be a misinterpretation in New Zealand, it may well occur elsewhere.
As in the case of lateral separation, the presentation and explanation of longitudinal separation in Doc 4444 is unsatisfactory.
It is recommended that
The matter of longitudinal separation( crossing tracks) be included in the action taken on WP61.
That the possibility of misinterpretation of these minima be brought to the attention of ICAO and IFALPA with the utmost dispatch.
Last Update: September 20, 2020