The US FAA has issued a draft update of an advisory circular (AC) that provides guidance on airworthiness approval for designers, manufacturers, and installers of satellite voice equipment supporting air traffic service (ATS).
Due to frequency congestion and ionospheric/solar conditions in oceanic and remote flight operations, aircraft operators requested the use of satellite voice equipment as one of their two long range communication systems, explained the FAA in its AC. It noted that certain implementations of the satellite voice system ground network utilize the public switched telephone network for flight safety communication, but have the potential for network congestion and audio level variability.
"Until these issues are addressed, air traffic control (ATC) use of the satellite voice system will be predicated upon having an alternate means of communication available appropriate for the airspace equipage requirements. For the foreseeable future, the availability of HF radio services will be required and satellite voice will coexist with high frequency (HF) radio," said the FAA.
In the AC, which is not mandatory, the agency describes an acceptable means - but not the only means - to gain airworthiness approval for satellite voice equipment.
Protocol includes meeting minimum performance standards, and ensuring software and hardware comply with various RTCA documents, as well as meeting various other safety requirements.
Satellite voice is considered voice communication for the purpose of the operating rules pertaining to CVR. As such, a means should be provided to record all flight crew satellite voice communications in crash survivable memory, if a cockpit voice recorder is required, according to the FAA. A means should also be provided to interface with the existing audio management system, it said.
Flight tests for certification should evaluate the integration of the satellite voice system with other systems, and evaluate other systems as necessary to show the satellite voice system does not interfere with their operation. Specific attention should be given to other "L" band equipment, said the FAA, particularly the global positioning system (GPS) equipment. "Intermodulation effects are possible between multiple channel satcom installations and GPS," it added.