World Air Ops | NAT | Doc 007 MNPS Guidance

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Guidance concerning Air Navigation in and above the NAT MNPSA CHAPTER 1212.5.2 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 manyroutes all adjacent flights levels are simultaneously used for a given traffic flow. While this arrangementmay not be unique, it is not one that is commonly employed in many other areas of the world. As a resultmany, if not most, en-route wake vortex encounters outside the NAT Region arise from opposite directionpassings or route crossing situations. In the NAT Region en-route wake vortices are encountered morecommonly from a preceding aircraft following the same track, usually at the next higher level. In the earlydays of RVSM implementation in the NAT Region a number of such reported encounters led to thedevelopment of a “wake turbulence offset procedure”. This has now been subsumed into SLOP which is astandard operating procedure throughout the NAT Region and is required to mitigate the risk of verticalnavigation errors. Any pilot who encounters a wake turbulence event when flying in NAT MNPS Airspaceshould ensure that a detailed report is provided and that a copy is forwarded to the North Atlantic CentralMonitoring Agency. After the expiry of the current ICAO programme, and in the absence of any otherrelevant mandatory reporting arrangements, the reporting form included at Attachment 3 to this Manualcould be used for this purpose.12.5.3 The Strategic Lateral Offset Procedures (see Chapter 8) are now standard operatingprocedures throughout the NAT Region. Thus when flying within NAT MNPS Airspace, if the aircraftencounters wake turbulence and the pilot considers it necessary to offset from the current track then the pilotmay only elect to fly another of the three options allowable in SLOP (i.e. Cleared Track centre-line, or 1 NMor 2 NM right of centre-line). It is no longer possible to offset left of the track centre-line to avoid waketurbulence. If neither of the remaining SLOP offset tracks are upwind of the other aircraft which is causingthe wake turbulence, then the pilot should co-ordinate with the other aircraft via the inter-pilot frequency123.45 MHz, and perhaps request that the other aircraft adopt an alternative (SLOP) allowable downwindoffset. If wake turbulence is encountered, even if it is subsequently avoided by judicious use of offsets, areport should still be made. If turbulence is encountered but the pilot is unsure whether the cause is wakevortex or perhaps Clear Air Turbulence, a report should be submitted annotated to this effect.12.6 ACAS/TCAS ALERTS AND WARNINGS12.6.1 With effect from 01 January 2005 all turbine-engined aircraft with a certificated take-offmass exceeding 5,700 Kgs or authorised to carry more than 19 passengers are required to carry and operateACAS II in the NAT Region. It should be noted that TCAS Version 7.0 meets the ICAO technicalspecifications for ACAS II as described in ICAO Annex 10 Volume IV.12.6.2 The provisions relating to the carriage and use of ACAS II are contained in ICAO Annexes2, 6, 10 & 11 and in the Procedures for Air Navigation Services (PANS) Ops & ATM. Operationalprocedures are fully detailed in PANS-OPS Doc 8168, Volume 1, Part VIII, Chapter 312.6.3 All Resolution Advisories (RAs) should be reported to ATC:a) verbally, as soon as practicable; andb) in writing, to the Controlling Authority, after the flight has landed, using the necessaryprocedure 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 procedure12.6.4 TCAS registers targets up to 40 NMs. Depending upon OAT/ambient air density, a Mach ofabout 0.85 equates to a TAS of approx 480 Kts, or 8 NMs per minute. Since the longitudinal separationstandard employed in the North Atlantic is 10 minutes, pilots would consequently not normally expect theirTCAS to register targets at the same level, whether these may be in-trail, crossing, climbing or descendingNAT Doc 007 80 Edition 2010
Guidance concerning Air Navigation in and above the NAT MNPSA CHAPTER 12through their level. However, since January 2009, some NAT ATC units are utilising a procedure whichpermits ATC to clear an aircraft to climb or descend through the level of another aircraft, with as little as 5minutes longitudinal separation, provided that both aircraft are using GNSS (GPS) for position determinationand reporting. Many NAT aircraft request and are cleared at lesser Machs than 0.85. A 5 minutes in trailseparation between two aircraft flying at M0.80 and experiencing a headwind component of 30 Kts (notunusual for W/B NAT flights), will equate to approx 35 NMs. Furthermore, depending upon therounding/truncating protocols used by pilots, FMSs and/or ATC Flight Data Processing Systems (for“minutes and seconds” to “minutes”), a nominal 5 minutes separation can in fact be close to an actual 4minutes (it can, of course, also be 6 minutes). In such a circumstance the actual longitudinal separationcould be less than 30 NMs. In these cases TCAS may register targets.12.6.5 The rule allowing ATC to use this procedure includes a caveat that the climb or descentneeds to be undertaken within 10 minutes of the time that the second aircraft in the pair has passed acommon reporting point. Consequently, the pilot of an aircraft cleared for a climb or descent of more than asingle flight level, should be alerted to the possibility of a potential TCAS alert by the controller’s use of theconditional phrase “By” or “At or Before” in the clearance received. However, the pilot of the “passiveparticipant” aircraft of the 5 minutes separated pair, if it is the following aircraft, could be presented with a“pop-up” TCAS target without such a warning. The bulletin announcing the introduction of this procedurein the North Atlantic includes the following instruction;- “If there is any concern regarding the proximity ofanother aircraft, flight crews must not hesitate to clarify the situation and take appropriate action to ensurethe safety of the flight.” However, given the air/ground communications methods employed in the NAT, thepilot may not receive a response to such a request for “clarification” prior to the other aircraft passing itsflight level. Nevertheless, even at these separations, Resolution Advisories are not anticipated and it is notexpected that pilots will consider deviating from their clearance as “appropriate action”.NAT Doc 007 81 Edition 2010
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World Air Ops | NAT | Doc 007 MNPS Guidance

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