Guidance concerning Air Navigation in and above the NAT MNPSA
checking the distance from the ramp position to the first waypoint. Some systems will account for the track distance involved in an ATC SID; in others, an appropriate allowance for a SID may have to be made to the great circle distance indicated in order to match that in the Master Document. If there is significant disagreement, rechecking initial position and waypoint co-ordinates may be necessary.
selecting track waypoint 1 to waypoint 2 and doing the following:
checking accuracy of the indicated distance against that in the Master Document;
checking, when data available, that the track displayed is as listed in the Master Document. (This check will show up any errors made in lat/long designators (i.e. N/S or E/W).)
similar checks should be carried out for subsequent pairs of waypoints and any discrepancies between the Master Document and displayed data checked for possible waypoint insertion errors. These checks can be co-ordinated between the two pilots checking against the information in the Master Document.
when each leg of the flight has been checked in this manner it should be annotated on the Master Document by means of a suitable symbology as previously suggested (See "The Use of a Master Document” above).
some systems have integral navigation databases and it is essential that the recency of the database being used is known. It must be recognised that even the co-ordinates of waypoint positions contained in a data base have been keyed in at some point by another human. The possibility of input errors is always present. Do not assume the infallibility of navigation databases and always maintain the same thorough principles which are applied in the checking of your own manual inputs.
Leaving the Ramp
The aircraft must not be moved prior to the navigation mode being initiated, otherwise
inertial navigation systems must be realigned. Prior to leaving the ramp Zero Ground Speed indications from the LRNS should be confirmed. Any excessive Ground Speeds noted while on chocks should be resolved by
checking fault codes, the currency of data bases and RAIM (if GPS is employed).
After leaving the ramp, inertial groundspeeds should be checked (a significantly erroneous
reading may indicate a faulty or less reliable inertial unit). A check should be made on any malfunction codes whilst the aircraft is stopped but after it has taxied at least part of the way to the take-off position; any significant ground-speed indications whilst stationary may indicate a faulty inertial unit such as a tilted platform. Prior to take-off, operators with an avionic fit which employs an electronic map display should
confirm that the derived position indicates that the aircraft is at the start of the runway.
Many modern aircraft are equipped with FMS navigation systems (i.e. Flight Management
Computers fed by multiple navigation sensors.). Once the FMS is put into 'Nav' mode, the system decides on the most appropriate (i.e. accurate) navigation sensors to use for position determination. If GPS is part of the solution, then the position is normally predominantly based on GPS inputs with the IRS/INS in a supporting role. It may therefore be difficult to know exactly what component of the navigation solution (IRS, GPS, DME etc) is being used to derive position at any one time. With an FMS-based system, or a GPS stand-alone system, the “Leaving the Ramp” checks should be designed to provide assurance that the
navigation information presented is indeed 'sensible'.
NAT Doc 007