Guidance concerning Air Navigation in and above the NAT MNPSA
noted that some aircraft clocks can only be re-set while the aircraft is on the ground. (See further comments on time-keeping/longitudinal navigation in Chapter 1 and Chapter 8.)
In the application of Mach Number Technique, pilots must adhere strictly to their assigned
True Mach Numbers unless a specific re-clearance is obtained from the appropriate ATC unit. However, as the aircraft weight reduces it may be more fuel efficient to adjust the Mach Number. Since the in-trail and crossing track separations between individual aircraft are established on the basis of ETAs passed to, or 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 immediate temporary
Cruise or ECON 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 be familiar with a procedure in those areas which permits pilots to unilaterally mach number by up to 0.02M, without prior ATC approval. This is not the
than the North Atlantic, may elect to change their cruising case in the North Atlantic
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.
PROCEDURE AFTER LEAVING OCEANIC AIRSPACE
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.
NAT Doc 007