Guidance concerning Air Navigation in and above the NAT MNPSA
For Receiver Autonomous Integrity Monitoring (RAIM) purposes:
Five satellites are required to detect the presence of a single faulty satellite;
For Fault Detection and Exclusion (FDE) purposes:
Six satellites are required to identify a faulty satellite and exclude it from participating in
further navigation solution calculations. associated with a RAIM algorithm).
(Note that an FDE algorithm is normally
Note: the above numbers of satellites (for RAIM and FDE purposes only) may in each case be reduced by one if barometric aiding is used.
Satellite Navigation Prediction
When so required, operators intending to conduct GPS navigation in MNPS Airspace must
utilise a Satellite Navigation Availability Prediction Programme specifically designated for the GPS equipment installed. This prediction programme must be capable of predicting, prior to departure for flight on a "specified route"*, the following:
Any loss of navigation coverage (meaning that less than 3 satellites will be in view to the receiver);
Any loss of the RAIM function and its duration.
"speci ied route" is de ined by a series of waypoints (to perhaps include the route to any alternate), with the time between waypoints based on planned speeds. Since light
planned ground speeds and/or
departure times may not be met, the pre-departure prediction must
be performed for a range of expected ground speeds.
This prediction programme must use appropriate parameters from the RAIM algorithm
employed by the installed GPS equipment. In order to perform the predictions this programme must provide the capability to manually designate satellites that are scheduled to be unavailable. Such information is not included in the GPS almanac or ephemeris data in the navigation message (i.e. the GPS receiver does not receive this information). Information on GPS satellite outages is promulgated via the U.S. NOTAM Office. The KNMH transmitting station (US Coast Guard Station, Washington D.C.) is responsible for release (in NOTAM format) of information relating to the operating condition of the GPS constellation satellites. These NOTAMs can be obtained through direct query to the USA data bank, via the AFTN, using the following service message format : SVC RQ INT LOC = KNMH addressed to KDZZNAXX. Such information can
also be found on the US Coastguard Web site at http://www.navcen.uscg.gov ."
When GPS is being used as a supplementary navigation means or when GPS is only one of
the two LRNSs required for MNPS approval (e.g. when the second LRNS is an IRS/INS installation) then
some States of Registry may not require the operator to conduct pre-flight RAIM prediction checks.
Operational Control Restrictions
The Capability to determine a GPS position
Prior to departure, the operator must use the prediction programme to first demonstrate that
forecast satellite outages will not result in a loss of navigation coverage (i.e. the capability to determine position) on any part of the specified route of flight. If such outages are detected by the programme, the
flight will need to be re-routed, delayed or cancelled.
Determination of the Availability of RAIM
Once the position determination function is assured (i.e. no loss in navigation coverage for
the route has been predicted), the operator must run the RAIM outage prediction programme. Any
NAT Doc 007