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Navigation Aids

2. By telephone to the nearest ATC facility

controlling the airspace where the disruption was


3. Additionally, GNSS problems should be

reported by Internet via the GPS Anomaly Reporting

Form at


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.


GPS interference or outages associated with known

testing NOTAMs should not be reported to ATC.

1−1−14. LORAN 



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 Operators should also note



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

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 constella-

tion and monitors the GPS satellites to ensure proper

operation. Each satellite’s orbital parameters (eph-

emeris data) are sent to each satellite for broadcast as


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