Home' RTCA Documents for Review : DO-343B Contents 57
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such services with other communication, navigation, and surveillance radios operating
on the same aircraft and in the same airspace. A significant caveat to this intent is the
ability to support simultaneous independent operation of both Iridium and Inmarsat
AES terminals on the same aircraft without a demonstrated means of
cooperation. Owners, operators and installers are cautioned that simultaneous
independent operation of Inmarsat and Iridium AES equipment on the same aircraft
has the potential to cause significant interference to all Iridium AMSS and AMS(R)S
services. This caution applies to Inmarsat equipment that is compliant with RTCA DO-
210D, including all changes, ARINC Characteristic 741, ARINC Characteristic 761,
ARINC Characteristic 781, and the AES requirements on SBB-based service
equipment described in the most recent edition of DO-262. At the time of publication
of this document, simultaneous independent operation of Inmarsat and Iridium
equipment on the same aircraft had been reported in special cases. However, no
generally applicable and technically feasible means of mitigating the potential for
interference could be identified.
This caveat specifically excludes installations where Inmarsat and Iridium are intended
for use in separate airspace. For example, no special installation or other
considerations are required for Iridium use in polar airspace that is outside of the
coverage volume of the Inmarsat services described in this document.
At the time of publication of this document, there is no regulatory guidance nor
AMS(R)S operational need to require Inmarsat and Iridium systems to work
simultaneously on the same aircraft. Some operators may choose to use Iridium and
Inmarsat as backup or in a non-simultaneous mode of operation.
3.6.3 Iridium AMS(R)S in the same airspace
The caveats of the previous paragraph apply to simultaneous independent operation
of Inmarsat and Iridium AMS(R)S or AMSS on the same aircraft. ICAO Aeronautical
Communications Panel, Working Group M in 2008 accepted analyses indicating that
Inmarsat safety and non-safety communications using both SBB and Classic Aero
services do not induce harmful interference to Iridium AMS(R)S equipment on other
aircraft operating under 30/30 nautical mile separation in procedural airspace.
Appendix C to this attachment develops an interference model for the effects of
Inmarsat SBB transmissions on Iridium Block 1 transceivers operating in controlled
airspace. For the purpose of Appendix C, the controlled airspace is assumed to be
Core Europe, within a 300 nmi radius of Brussels. Appendix C reaches four
conclusions. All of these conclusions apply to TMA airspace above the approach and
landing, takeoff, taxi, and gate segments of flight.
1. The probability of undesired signal out of band and spurious emissions from a
single Inmarsat SBB transmitter causing interference to a message arriving at
a single Iridium Block 1 receiver operating in the same Core Europe Airspace
is small, on the order of
, depending on the specific terminal type
and emissions type.
2. Despite recent changes to the receiver susceptibility specification for Iridium
Block 1 receivers contained in DO-262B, Change 1, the probability of desired
signal from a single Inmarsat SBB transmitter to a message arriving at a single
Iridium Block 1 receiver operation in the same Core Europe airspace is also
small, on the order of
3. The probability of undesired signal out of band and spurious emissions from a
single of Inmarsat SBB transmitter causing interference to a multiplicity of
Iridium Block 1 aircraft operating in the same Core Europe Airspace is
4. The probability of desired signal from the ensemble of simultaneously
transmitting Inmarsat SBB transmitters causing significant interference to a
large number of Iridium Block 1 receivers operating in the same Core Europe
Airspace is very small.
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