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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
flight should be re-routed, delayed or cancelled. It is understood that some prediction programmes carry out
both these checks together.
Note - 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 aircraft away from track at a
speed of 35 knots. With the current MNPS track spacing of 60 nautical miles, it is further assumed
that aircraft on adjacent tracks have a lateral “safety buffer” of 30 nautical miles. At 35 knots it
will take an aircraft 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
8.3.14 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.
8.3.15 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 aircraft operating in MNPS airspace have an
IRS/INS as part of their Long Range navigation fit. An increasing number of those with IRS/INS
also have GPS and whilst GPS may then be considered the primary LRNS, these aircraft are still
required to input the ramp position. This should then be compared with the GPS solution. For
those few aircraft 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
NORTH ATLANTIC MNPSA OPERATIONS MANUAL CHAPTER 8
NAT MNPS 47 Edition 2009
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 sufficient
satellites are in view the most likely causes are GPS receiver error, atmospheric interference, or,
incorrect ramp co-ordinates.
8.3.16 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
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