background image

AIM

10/12/17

1−1−31

Navigation Aids

4. Air carrier and commercial operators must

meet the appropriate provisions of their approved

operations specifications.

5. Prior to GPS/WAAS IFR operation, the pilot

must review appropriate Notices to Airmen (NOT-

AMs) and aeronautical information. This

information is available on request from a Flight

Service Station. The FAA will provide NOTAMs to

advise pilots of the status of the WAAS and level of

service available.

(a) The term MAY NOT BE AVBL is used in

conjunction with WAAS NOTAMs and indicates that

due to ionospheric conditions, lateral guidance may

still be available when vertical guidance is

unavailable. Under certain conditions, both lateral

and vertical guidance may be unavailable. This

NOTAM language is an advisory to pilots indicating

the expected level of WAAS service (LNAV/VNAV,

LPV, LP) may not be available.

EXAMPLE−

!FDC FDC NAV WAAS VNAV/LPV/LP MINIMA MAY

NOT BE AVBL 1306111330-1306141930EST 

or 

!FDC FDC NAV WAAS VNAV/LPV MINIMA NOT AVBL,

WAAS LP MINIMA MAY NOT BE AVBL

1306021200-1306031200EST

WAAS MAY NOT BE AVBL NOTAMs are

predictive in nature and published for flight planning

purposes. Upon commencing an approach at

locations NOTAMed WAAS MAY NOT BE AVBL,

if the WAAS avionics indicate LNAV/VNAV or LPV

service is available, then vertical guidance may be

used to complete the approach using the displayed

level of service. Should an outage occur during the

approach, reversion to LNAV minima or an alternate

instrument approach procedure may be required.

When GPS testing NOTAMS are published and

testing is actually occurring, Air Traffic Control will

advise pilots requesting or cleared for a GPS or

RNAV (GPS) approach that GPS may not be

available and request intentions. If pilots have

reported GPS anomalies, Air Traffic Control will

request the pilot’s intentions and/or clear the pilot for

an alternate approach, if available and operational.

(b) WAAS area-wide NOTAMs are origin-

ated when WAAS assets are out of service and impact

the service area. Area−wide WAAS NOT AVAIL-

ABLE (AVBL) NOTAMs indicate loss or

malfunction of the WAAS system. In flight, Air

Traffic Control will advise pilots requesting a GPS or

RNAV (GPS) approach of WAAS NOT AVBL

NOTAMs if not contained in the ATIS broadcast.

EXAMPLE−

For unscheduled loss of signal or service, an example

NOTAM is: !FDC FDC NAV WAAS NOT AVBL

1311160600− 1311191200EST.  

For scheduled loss of signal or service, an example

NOTAM is: !FDC FDC NAV WAAS NOT AVBL

1312041015- 1312082000EST.

(c) Site−specific WAAS MAY NOT BE

AVBL NOTAMs indicate an expected level of

service; for example, LNAV/VNAV, LP, or LPV may

not be available. Pilots must request site−specific

WAAS NOTAMs during flight planning. In flight,

Air Traffic Control will not advise pilots of WAAS

MAY NOT BE AVBL NOTAMs.

NOTE−

Though currently unavailable, the FAA is updating its

prediction tool software to provide this site-service in the

future.

(d) Most of North America has redundant

coverage by two or more geostationary satellites. One

exception is the northern slope of Alaska. If there is

a problem with the satellite providing coverage to this

area, a NOTAM similar to the following example will

be issued:

EXAMPLE−

!FDC 4/3406 (PAZA A0173/14) ZAN NAV WAAS SIGNAL

MAY NOT BE AVBL NORTH OF LINE FROM

7000N150000W TO 6400N16400W. RMK WAAS USERS

SHOULD CONFIRM RAIM AVAILABILITY FOR IFR

OPERATIONS IN THIS AREA. T-ROUTES IN THIS

SECTOR NOT AVBL. ANY REQUIRED ALTERNATE

AIRPORT IN THIS AREA MUST HAVE AN APPROVED

INSTRUMENT APPROACH PROCEDURE OTHER

THAN GPS THAT IS ANTICIPATED TO BE OPERA-

TIONAL AND AVAILABLE AT THE ESTIMATED TIME

OF ARRIVAL AND WHICH THE AIRCRAFT IS

EQUIPPED TO FLY. 1406030812-1406050812EST .

6. When GPS−testing NOTAMS are published

and testing is actually occurring, Air Traffic Control

will advise pilots requesting or cleared for a GPS or

RNAV (GPS) approach that GPS may not be

available and request intentions. If pilots have

reported GPS anomalies, Air Traffic Control will

request the pilot’s intentions and/or clear the pilot for

an alternate approach, if available and operational.

EXAMPLE−

Here is an example of a GPS testing NOTAM: 

!GPS 06/001 ZAB NAV GPS (INCLUDING WAAS, GBAS,