Guidance concerning Air Navigation in and above the NAT MNPSA
continuous outage of RAIM capability of greater than 51 minutes in MNPS airspace means again that the flight should be re-routed, delayed or cancelled. It is understood that some prediction programmes carry out both these checks together.
Derivation of the 51 minute limit – At the instant the RAIM capability is lost, it is
assumed that the GPS navigation solution proceeds to direct the aircra t away from track at a speed of 35 knots. With the current MNPS track spacing of 60 nautical miles, it is further assumed that aircra t on adjacent tracks have a lateral “safety buffer” of 30 nautical miles. At 35 knots it will take an aircra t 51 minutes to exit this “safety buffer”. It should be noted that this is a very conservative methodology and it is thought unlikely that a RAIM outage alone could cause such
errant navigation behaviour.
Loading of Initial Waypoints
The manual entry of waypoint data into the navigation systems must be a co-ordinated
operation by two persons, working in sequence and independently: one should key in and insert the data, and subsequently the other should recall it and confirm it against source information. It is not sufficient for
one crew member just to observe or assist another crew member inserting the data.
The ramp position of the aircraft, plus at least two additional waypoints, or, if the onboard
equipment allows, all the waypoints relevant to the flight, should be loaded while the aircraft is at the ramp.
However, it is more important initially to ensure that the first en route waypoint is inserted accurately.
Note - The vast majority of commercial air transport aircra t operating in MNPS airspace have an IRS/INS as part of their Long Range navigation it. An increasing number of those with IRS/INS also have GPS and whilst GPS may then be considered the primary LRNS, these aircra t are still required to input the ramp position. This should then be compared with the GPS solution. For those few aircra t with GPS as the only LRNS, whilst there may be no need to actually load the ramp position, it is good airmanship and recommended operational practice to compare the published ramp position with the GPS-derived position. Without selective availability GPS should give a position within 30 metres of the published ramp position. If the GPS position is more than 100 metres from the published ground position, then the cause should be investigated. If suf icient satellites are in view the most likely causes are GPS receiver error, atmospheric interference, or, incorrect ramp co-ordinates.
During flight, at least two current waypoints beyond the leg being navigated should be
maintained in the Control Display Units (CDUs) until the destination ramp co-ordinates are loaded. Two pilots should be responsible for loading, recalling and checking the accuracy of the inserted waypoints; one loading and the other subsequently recalling and checking them independently. However, this process should not be permitted to engage the attention of both pilots simultaneously during the flight. Where remote loading of the units is possible, this permits one pilot to cross-check that the data inserted
automatically is indeed accurate.
An alternative and acceptable procedure is for the two pilots silently and independently to
load their own initial waypoints and then cross-check them. The pilot responsible for carrying out the verification should work from the CDU display to the Master Document rather than in the opposite direction. This may lessen the risk of the pilot 'seeing what is expected to be seen’ rather than what is actually
Flight Plan Check
The purpose of this check is to ensure complete compatibility between the data in the Master
Document and the calculated output from the navigation systems. Typical actions could include:
NAT Doc 007