Guidance concerning Air Navigation in and above the NAT MNPSA
Wake vortex encounters are, however, also experienced en-route, although less frequently.
To accommodate the predominantly uni-directional diurnal traffic flows through the NAT Region, on many routes all adjacent flights levels are simultaneously used for a given traffic flow. While this arrangement may not be unique, it is not one that is commonly employed in many other areas of the world. As a result many, if not most, en-route wake vortex encounters outside the NAT Region arise from opposite direction passings or route crossing situations. In the NAT Region en-route wake vortices are encountered more commonly from a preceding aircraft following the same track, usually at the next higher level. In the early days of RVSM implementation in the NAT Region a number of such reported encounters led to the development of a “wake turbulence offset procedure”. This has now been subsumed into SLOP which is a standard operating procedure throughout the NAT Region and is required to mitigate the risk of vertical navigation errors. Any pilot who encounters a wake turbulence event when flying in NAT MNPS Airspace should ensure that a detailed report is provided and that a copy is forwarded to the North Atlantic Central Monitoring Agency. After the expiry of the current ICAO programme, and in the absence of any other relevant mandatory reporting arrangements, the reporting form included at Attachment 3 to this Manual
could be used for this purpose.
The Strategic Lateral Offset Procedures (see Chapter 8) are now standard operating
procedures throughout the NAT Region. Thus when flying within NAT MNPS Airspace, if the aircraft encounters wake turbulence and the pilot considers it necessary to offset from the current track then the pilot may only elect to fly another of the three options allowable in SLOP (i.e. Cleared Track centre-line, or 1 NM or 2 NM right of centre-line). It is no longer possible to offset left of the track centre-line to avoid wake turbulence. If neither of the remaining SLOP offset tracks are upwind of the other aircraft which is causing the wake turbulence, then the pilot should co-ordinate with the other aircraft via the inter-pilot frequency 123.45 MHz, and perhaps request that the other aircraft adopt an alternative (SLOP) allowable downwind offset. If wake turbulence is encountered, even if it is subsequently avoided by judicious use of offsets, a report should still be made. If turbulence is encountered but the pilot is unsure whether the cause is wake
vortex or perhaps Clear Air Turbulence, a report should be submitted annotated to this effect.
ACAS/TCAS ALERTS AND WARNINGS
With effect from 01 January 2005 all turbine-engined aircraft with a certificated take-off
mass exceeding 5,700 Kgs or authorised to carry more than 19 passengers are required to carry and operate
ACAS II in the NAT Region.
It should be noted that TCAS Version 7.0 meets the ICAO technical
specifications for ACAS II as described in ICAO Annex 10 Volume IV.
The provisions relating to the carriage and use of ACAS II are contained in ICAO Annexes
2, 6, 10 & 11 and in the Procedures for Air Navigation Services (PANS) Ops & ATM. procedures are fully detailed in PANS-OPS Doc 8168, Volume 1, Part VIII, Chapter 3
All Resolution Advisories (RAs) should be reported to ATC:
verbally, as soon as practicable; and
in writing, to the Controlling Authority, after the flight has landed, using the necessary
procedure and forms, including, when appropriate, the ‘Altitude Deviation Report Form’ shown at Attachment 2 to this Manual.
Possible traffic alerts resulting from ATC use of the 5 minutes GNSS climb/descent through procedure
TCAS registers targets up to 40 NMs. Depending upon OAT/ambient air density, a Mach of
about 0.85 equates to a TAS of approx 480 Kts, or 8 NMs per minute. Since the longitudinal separation standard employed in the North Atlantic is 10 minutes, pilots would consequently not normally expect their TCAS to register targets at the same level, whether these may be in-trail, crossing, climbing or descending
NAT Doc 007