2. By telephone to the nearest ATC facility
controlling the airspace where the disruption was
experienced.
3. Additionally, GNSS problems should be
reported by Internet via the GPS Anomaly Reporting
Form at http://www.faa.gov/air_traffic/nas/
gps_reports/.
c. In aircraft equipped with more than one avionics
receiver, there are many combinations of potential
interference between units that could cause
erroneous navigation indications, or complete or
partial blanking out of the display.
NOTE-

GPS interference or outages associated with known
testing NOTAMs should not be reported to ATC.
1-1-14. LORAN
NOTE-
In accordance with the 2010 DHS Appropriations Act, the
U.S. Coast Guard (USCG) terminated the transmission of
all U.S. LORAN-C signals on 08 Feb 2010. The USCG also
terminated the transmission of the Russian American
signals on 01 Aug 2010, and the Canadian LORAN-C
signals on 03 Aug 2010. For more information, visit
http://www.navcen.uscg.gov. Operators should also note
that TSO-C60b, AIRBORNE AREA NAVIGATION
EQUIPMENT USING LORAN-C INPUTS, has been
canceled by the FAA.

1-1-15. Inertial Reference Unit (IRU),
Inertial Navigation System (INS), and
Attitude Heading Reference System (AHRS)
a. IRUs are self-contained systems comprised of
gyros and accelerometers that provide aircraft
attitude (pitch, roll, and heading), position, and
velocity information in response to signals resulting
from inertial effects on system components. Once
aligned with a known position, IRUs continuously
calculate position and velocity. IRU position
accuracy decays with time. This degradation is
known as "drift."
b. INSs combine the components of an IRU with
an internal navigation computer. By programming a
series of waypoints, these systems will navigate along
a predetermined track.
c. AHRSs are electronic devices that provide
attitude information to aircraft systems such as

1-1-16

weather radar and autopilot, but do not directly
compute position information.
d. Aircraft equipped with slaved compass systems
may be susceptible to heading errors caused by
exposure to magnetic field disturbances (flux fields)
found in materials that are commonly located on the
surface or buried under taxiways and ramps. These
materials generate a magnetic flux field that can be
sensed by the aircraft"s compass system flux detector
or "gate", which can cause the aircraft"s system to
align with the material"s magnetic field rather than
the earth"s natural magnetic field. The system"s
erroneous heading may not self-correct. Prior to take
off pilots should be aware that a heading
misalignment may have occurred during taxi. Pilots
are encouraged to follow the manufacturer"s or other
appropriate procedures to correct possible heading
misalignment before take off is commenced.
1-1-16. Doppler Radar
Doppler Radar is a semiautomatic self-contained
dead reckoning navigation system (radar sensor plus
computer) which is not continuously dependent on
information derived from ground based or external
aids. The system employs radar signals to detect and
measure ground speed and drift angle, using the
aircraft compass system as its directional reference.
Doppler is less accurate than INS, however, and the
use of an external reference is required for periodic
updates if acceptable position accuracy is to be
achieved on long range flights.
1-1-17. Global Positioning System (GPS)
a. System Overview
1. System Description. The Global Positioning
System is a space-based radio navigation system
used to determine precise position anywhere in the
world. The 24 satellite constellation is designed to
ensure at least five satellites are always visible to a
user worldwide. A minimum of four satellites is
necessary for receivers to establish an accurate
three-dimensional position. The receiver uses data
from satellites above the mask angle (the lowest
angle above the horizon at which a receiver can use
a satellite). The Department of Defense (DOD) is
responsible for operating the GPS satellite constellation and monitors the GPS satellites to ensure proper
operation. Each satellite"s orbital parameters (ephemeris data) are sent to each satellite for broadcast as

Navigation Aids