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realignment feature is sometimes provided but should only be used if, during an intermediate stop, it
becomes necessary to increase the system accuracy. The aircraft must be stationary during rapid realignment
which typically will take about one minute.
8.3.4 To ensure that there is adequate time for the initial alignment, the first crew member on the
flight deck should normally put the inertial system(s) into the align mode as soon as practicable.
GNSS (GPS) Systems
8.3.5 As with all LRNS operations, GPS LRNS operations must be approved by the State of the
Operator (or the State of Registry for International General Aviation operations) as part of the MNPS
operational approval. When both the LRNSs required for unrestricted MNPS operations are GPSs the
approval of their operation will include the requirement to carry out Pre-Departure Satellite Navigation
Prediction Programmes (as shown below). When only one of the two LRNSs required is a GPS, State
Authorities vary as to whether they require their operators to conduct such pre-departure programmes.
Satellite Availability
8.3.6 Given suitable geometry:
- Four satellites are required to determine 3-D position;
8.3.7 For Receiver Autonomous Integrity Monitoring (RAIM) purposes:
- Five satellites are required to detect the presence of a single faulty satellite;
8.3.8 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. (Note that an FDE algorithm is normally
associated with a RAIM algorithm).
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
8.3.9 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:
a) Any loss of navigation coverage (meaning that less than 3 satellites will be in view to the
receiver);
and
b) Any loss of the RAIM function and its duration.
*Note: "specified route" is defined by a series of waypoints (to perhaps include the route to any
required alternate), with the time between waypoints based on planned speeds. Since flight
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.
NORTH ATLANTIC MNPSA OPERATIONS MANUAL CHAPTER 8
NAT MNPS 46 Edition 2008
8.3.10 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 ."
8.3.11 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
8.3.12 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
8.3.13 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
continuous outage of RAIM capability of greater than 51 minutes in MNPS airspace means again that the
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