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coupled operation is provided in flight management systems
SEPARATION SAFETY MODELING
A-10
through the "engagement" of LNAV (two-dimensional) or
VNAV (three-dimensional) operation. The guidance "mode" of
operation is correlated with the "pilotage" or "flight technical
error" of the aircraft.
2) Navigation data bases are provided in the more sophisticated
systems. These may be updated on a 28-day cycle to keep
currency with navigation charting. Data bases may be
regional or international. Data bases typically contain radio
navigation aid positions, published navigation waypoint
locations, and terminal procedures (standard departure and
arrival routes, approach transitions, published holding
locations, etc.) For air carrier operations the navigation data
base is specified in the ARINC 424 document. Navigation data
bases allow lower workload "loading/changing" of the flight
plan with reduced probability of waypoint definition error.
3) Navigation displays may include digital maps which provide the
flight crew with a plan view display of the aircraft position and
flight plan selected for the flight. A map provides "situational"
awareness and helps detect errors in flight plan entry of
procedures.
4) Required navigation performance systems are among the
newest-generation of navigation systems. These systems
provide an estimate of position uncertainty (the current actual
navigation performance estimate (a 95% probability of being
within the estimated value) together with associated levels of
integrity and availability of the navigation function. RTCA
SC-181 has developed the standards for RNP-based
navigation.]
c. Communications capability
i. Voice communications systems
1) Commercial aircraft
a) Required communication performance
b) VHF systems (direct)
[VHF systems are "line of sight" limited, but of high
availability when in coverage. Concern about frequency
congestion of the VHF links is leading to consideration of
reduced channel spacing and digital radios for voice
communications.]
c) HF systems (indirect)
[HF systems are used for out-of-coverage communications,
over the ocean, for example. They are of lower availability
and (typically) there are transmission delays between
aircraft and ATC controller.]
2) Military aircraft
3) General aviation and other aircraft
APPENDIX A
FACTORS POTENTIALLY AFFECTING SEPARATION SAFETY
A-11
4) UHF
5) SATCOM (communication via satellite)
ii. ADS-B
iii. ACARS
[Provides digital data communications, primarily between pilot
and airline operational control. A few ATC applications are used
over ACARS (pre-departure clearance) and others have been
proposed. Satellite systems for long-range voice communications
are beginning to be used in oceanic operations. These systems
provide direct controller-to-pilot (CPDC) data communications.
Other potential future data link communications media have been
proposed, such as the Mode S data link and the use of Low Earth
Orbiting satellites (LEOs) to support ATC data communications.
Additionally, the Aeronautical Telecommunications Network
(ATN) is being developed as a system of protocols (open system)
and routers to provide inter-operability of communications media
between airplane and air traffic control.]
[iv. Remarks
Required communications performance is under development by
RTCA and EUROCAE to provide high-level performance
specification of air-ground communications for operation in a
given airspace. Factors to be considered include message delay,
availability, and integrity.]
d. Surveillance capability
i. Required surveillance equipment performance
ii. Air-ground transponder
[supports operation in controlled airspace]
1) Mode C transponder
[Provides the ATC-assigned aircraft identification (which may
not be unique) and pressure altitude quantized (rounded) in
100-ft. increments].
2) Mode S transponder
[Provides a unique aircraft-associated identification, potential
for other data transmissions, and pressure altitude quantized in
25-ft. increments.]
3) Mode A transponder
[Provides only ATC-assigned identification (which may not be
unique)]
iii. TCAS/ACAS (Traffic Alert and Collision Avoidance
System/Airborne Collision Avoidance System)
[Interrogates transponders of near-by aircraft to determine
proximity, relative trajectories and relative velocities, and to
provide collision avoidance advisories. TCAS, by ICAO mandate,
cannot be used as a basis of reduced separation standards, but
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a concept paper for separation safety modeling(61)
