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calculated by, ATC, it is essential that ATC approval is requested prior to effecting any change in cruise
Mach Number. Such approval will be given if traffic conditions permit. Pilots must recognise that
adherence to the assigned Mach Number is essential. No tolerance is provided for. Pilots must not
utilise Long Range Cruise or ECON FMC modes when transiting NAT MNPS airspace. If an
immediate temporary change in the Mach Number is essential, e.g. due to turbulence, ATC must be notified
as soon as possible. Pilots with experience of flying in oceanic airspaces other than the North Atlantic, may
be familiar with a procedure in those areas which permits pilots to unilaterally elect to change their cruising
mach number by up to 0.02M, without prior ATC approval. This is not the case in the North Atlantic
MNPS airspace.
7.3.5 Pilots should maintain their last assigned Mach Number during step-climbs in oceanic
airspace. If due to aircraft performance this is not feasible ATC should be advised at the time of the request
for the step climb.
7.4 PROCEDURE AFTER LEAVING OCEANIC AIRSPACE
7.4.1 After leaving oceanic airspace pilots must maintain their assigned Mach Number in domestic
controlled airspace unless and until the appropriate ATC unit authorises a change.
NORTH ATLANTIC MNPSA OPERATIONS MANUAL CHAPTER 8
NAT MNPS 40 Edition 2009
Chapter 8: MNPS Flight Operation & Navigation Procedures
8.1 INTRODUCTION
8.1.1 The aircraft navigation systems necessary for flying in NAT MNPS Airspace are capable of
high-performance standards. However, it is essential that stringent cross-checking procedures are employed,
both to ensure that these systems perform to their full capabilities and to minimise the consequences of
equipment failures and possible human errors.
8.1.2 Navigation systems are continuously evolving and early editions of this Manual concentrated
on offering specific guidance on the use of individual systems. Rather than specifying the types of
equipment required for flying in defined airspace, current philosophy is to specify a Required Navigation
Performance (RNP), effectively a track-keeping capability. As an example, the navigation performance
accuracy of the aircraft population operating in airspace designated RNP X airspace would be expected to be
better than X NM on a 95% containment basis. The NAT Minimum Navigation Performance Specifications
(MNPS) inter alia define a requirement for the standard deviation of lateral track errors to be less than
6.3 NM. Since two standard deviations provide for about 95 % containment, the MNPS statement is
effectively akin to an RNP value of 12.6 in a lateral sense. It is also perhaps interesting to note that actual
measurements of the achieved navigation performance by the entire fleet of NAT aircraft, even before GPS
came into use by a large proportion, indicated an achieved standard deviation of approximately 2 NM.
Note: - Continued development within ICAO of the concept of navigation performance
specifications is leading to the future replacement of the current system of RNP with a
“Performance Based Navigation (PBN)” philosophy. Within this new philosophy, navigation
specifications not requiring automatic monitoring and alerting will be known as RNAV.
Navigation specifications which do require monitoring and alerting will be known as RNP. With
current technology, on-board performance monitoring can only be carried out by aircraft fitted
with GPS. Hence, GPS will be mandatory for RNP airspace. MNPS airspace navigation does not
require an on-board automatic monitoring and alerting function. Instead pilots must remain
vigilant and employ rigorous routine manual monitoring procedures.
8.1.3 MNPS was devised and implemented in the NAT Region long before the RNP concept was
developed. MNPS was established primarily with the NAT OTS environment in mind. The defining
waypoints of OTS tracks are specified by whole degrees of latitude and, using an effective 60 NM lateral
separation standard, most adjacent tracks are separated by only one degree of latitude at each ten-degree
meridian. The traffic density in the OTS is higher than in any other oceanic airspace. In such a densely
populated flexible track system (one that changes twice every day), it is essential that crews avoid (whole
degree) waypoint insertion errors. Such errors in the NAT MNPSA will inevitably result in a conflict with
traffic on an adjacent track. For this reason Minimum Navigation Performance Specifications had to include
not just the technical navigation accuracy of the Long-range Navigation Systems used on the aircraft but also
the crew navigation procedures employed. The MNPS statement thus involves both cockpit/flight deck
procedures and crew training requirements. In the early days of the RNP concept, it was these additional
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