Navigation Equipment Flashcards
EGI (Modes/Alignment Types/Restrictions/Operation)
- Hybrid navigation (HNAV) — Performs integrated inertial/GPS navigation providing a hybrid (both GPS
and inertial data “aiding” each other) solution with the GPS data used to bound inertial error growth and
inertial data being used to aid the GPS. HNAV is also an alignment type and can be initiated on ground,
ship, or in flight. - Inertial navigation (INAV) — Performs inertial-sensor-data-only navigation that is not free inertial, but
remains coupled to the EGI-filtered aircraft position. This navigation mode can be initiated on ground,
ship, or in flight, using any of the alignment types below, independent of GPS availability.
There are five alignment types:
1. GPS/INS — This is the default alignment type which combines the INS and GPS to result in a Hybrid
Navigation (HNAV) mode of operation. This alignment type assumes the aircraft is in motion. It can be
commanded on the ground and in flight.
2. Gyrocompass (GC) — A GC alignment supports alignment of an inertial reference frame and determines
true heading when the helicopter is not in motion. This alignment type can be established on the ground
only.
3. Stored Heading (SH) — A SH alignment is used when valid heading is available to initialize alignment
processing (such as from a previous GC alignment and the helo has not moved). It can be considered
a submode of the GC alignment, both of which provide INAV solutions and assume that the aircraft is
stationary. This alignment type can be initiated on the ground only.
4. Directional Gyro (DG) — DG alignment provides attitude and true heading outputs to support a quick
launch capability. The DG alignment provides an INAV solution and is considered a degraded mode of EGI
operation. DG alignments are to be used only until time permits a normal, full alignment ( HNAV or INAV).
This alignment type can be initiated on ground, ship, or with Sys Config 18, in flight.
5. Data Link (DL) — DL alignment supports alignment of an inertial reference frame using ownship heading
and speed as a starting point. Determines attitude and true and mag heading. This alignment type can be
established shipboard.
INS (Restrictions/Mission Impacts)
A position error of less than or equal to 2.0 nm per hour of elapsed time is acceptable. (CH 7.7.14)
INS will be inaccurate over time, but it is completely internal and cannot be spoofed
GPS (Antennas/Operation/Spoofing)
The GPS antenna system (GAS-1) is a seven-element anti-jam controlled reception pattern antenna (CRPA) and an
antenna electronics (AE) unit . The AE unit nulls out suspected erroneous signals and passes “good” signals to the
EGI navigation system. In case of an AE failure, a backup fixed reception pattern antenna (FRPA) will provide a
GPS signal to EGI 2, utilizing a relay box called the data transfer interface unit (DTIU).
For those aircraft with GAS-1 installed, both EGIs are connected to GAS-1; EGI 2 automatically connects to
SATCOM/GPS (FRPA) in the event of a GAS-1 failure. EGI 1 has no backup.
TACAN (Operations/Restrictions)
The tactical air navigation (TACAN) set is made up of an R/T (located in the transition section), the upper TACAN
antenna, and the lower V/UHF/TACAN antenna. The TACAN set is used for position fixing, maintaining course
track, and navigating airways. It receives UHF (L band) signals from ground or shipboard stations and computes
magnetic bearing and slant range to the station. Station identification codes are conveyed by audio modulation of
the signal. Usable range of the TACAN set is limited to LOS, which increases with altitude. There are 252 TACAN
channels available for use: 126 X channels (for FAA use) and 126 Y channels (for tactical use). TACAN range
and bearing data is displayed on the FDs (via the ARINC 582 data bus) and provided to the mission computers for
navigation system processing (via the 1553B data bus). Power is supplied to the R/T from the No. 2 DC Primary
bus through the TACAN R/T circuit breaker
VOR/ILS Capabilities
The VHF omnidirectional ranging and instrument landing system (VOR/ILS) set is made up of one receiver (located
in the transition section), two VOR/localizer antennas, one ILS glideslope antenna, and one marker beacon antenna.
The VOR component is used for position fixing, maintaining course track, and navigating airways. It receives VHF
signals from ground stations and computes magnetic bearing to the station. The ILS component is used for precision
guidance during final approach to a runway. It receives VHF signals from ground stations that provide lateral
(localizer), along course (marker beacon), and vertical (glideslope) guidance. Usable range of the VOR/ILS set is
limited to LOS. The VOR operates in the 108.1 to 117.95 MHz frequency range with a total of 160 channels. The
localizer operates in the 108.1 to 112.0 MHz frequency range with a total of 40 channels. The glideslope operates
in the 329.15 to 335.0 MHz frequency range. The marker beacon operates at 75 MHz. Localizer and glideslope
frequencies are paired; selecting a localizer frequency automatically selects the glideslope frequency. VOR and
localizer transmitters have voice and Morse code station identifiers. Power is supplied from the No. 1 DC Primary
bus through the VOR/ILS RCVR circuit breaker.
