SATVOICE / SATCOM
The use of satellite voice systems for air traffic control has evolved over the years but has been made complicated by the variety of systems on aircraft versus systems that have proliferated in space. In other words, if your manufacturer guessed wrong about the way things were headed, your aircraft may not be as prepared as others.
First some terminology. We grew up with Satellite Communications (SATCOM) to mean picking up a phone and making a call via satellite. But now we have a myriad of systems that use the same satellites to transmit and receive all sorts of data. So SATCOM includes the data and the voice; we speak of SATVOICE to denote the picking up the phone bit.
Can you use SATVOICE to make a position report? In most parts of the world, yes. Can you use SATVOICE to replace the requirement for an HF? No, you still need at least one HF. Can you plan on using SATVOICE for air traffic services with an HF as backup? If the region you are flying has made such provisions and you have a qualified system, yes. But how do you know your system qualifies? The easiest way to tell is to look at your MMEL. More about that: LRCS to be Carried on Board
Figure: Aeronautical SATVOICE system overview, from SVGM, Figure 2-1.
- Historical Background
- SATVOICE System Overview
- SATVOICE as a Long Range Communications System
- LRCS to be Carried on Board
- Flight Crew Procedures
- Example Aircraft SATVOICE LRCS Discussion
- ARINC SATCOM Voice Procedures
- Data Link on VHF vs. SATCOM
- Line of Sight and Curvature of the Earth Issues
We've come a long way with satellite communications and there are changes in our near future . . .
[ICAO SVGM, pg. vi]
- In procedural airspace, aeronautical communications have historically been conducted with high frequency (HF) radios due to the advantage of being able to transmit and receive air-ground communications for thousands of miles. Most appropriate authorities hence required two independent HF sets on-board.
- The potential for improvement in efficiency resulting from the adoption of satellite technology was discussed at length during the Limited NAT Regional Air Navigation (LIM/NAT/RAN) Conference in Cascais, Portugal, in 1992. Although both data and voice communications were evaluated, it was recognised that data offered greater economic benefit and that the emphasis should be put on that form of communications. This was not seen as precluding the use of voice in abnormal circumstances but the use of SATCOM voice for routine communications was not seen as viable.
- In 1995, the initial future air navigation system (FANS 1/A) provided an integrated airborne CNS package. In addition to required navigation performance (RNP) and global navigation satellite system (GNSS) capabilities, FANS 1/A includes controller pilot data link communications (CPDLC) and automatic dependent surveillance – contract (ADS-C) capabilities using SATCOM, VHF, and HF data links. CPDLC and ADS-C were seen as the normal or preferred means of ATS communications and surveillance in procedural airspace. However, voice communications would continue to be required as an alternative means of ATS communications. At the same time, aircraft were equipped with SATVOICE capability.
- In 2008, the 44th Meeting of the NAT SPG (17-20 June 2008) agreed that authorization to use SATVOICE for all ATS communications would permit reduction in risk of communications failure, improve safety of operations, and alleviate HF channel congestion. However, guidance material would be needed to address a number of issues related to call setup times, security and system performance and capacity. It was further concluded that any decision regarding Minimum Equipment List (MEL) relief of one HF radio was subject to approval by the appropriate authority. This work resulted in NAT SPG Conclusion 45/28 endorsing a proposal for amendment to the NAT SUPPS Doc 7030 that removed the above-mentioned provision.
Most appropriate authorities seem to be quiet on this subject and it appear you only need one HF in most areas.
SATVOICE System Overview
[14 CFR 1] Long-range communication system (LRCS). A system that uses satellite relay, data link, high frequency, or another approved communication system which extends beyond line of sight.
[ICAO SVGM, ¶2.2.2] Satellite communication systems are defined by three different altitude orbits; low earth orbit (LEO), medium earth orbit (MEO) and geosynchronous earth orbit (GEO). The altitude of the orbit determines the area illuminated by the satellite. The higher the orbit the weaker the signal is from the satellite, but it has a much larger footprint. Propagation loss is overcome by increased complexity of the antenna systems along with higher transmitter power. Conversely, a LEO satellite's footprint is much smaller requiring a higher number of satellites to provide coverage, but the antennas used are much simpler along with reduced radio frequency power requirement on the subscriber end. Also, the lifetime of a LEO satellite is less due to drag caused by the close proximity of earth.
[ICAO SVGM, ¶2.3] Iridium uses a constellation of 66 satellites at an altitude of 780 km (450 miles) in six orbital planes, with eleven satellites in each orbital plane, providing global coverage. Additionally there are a number of spare satellites to replace any in-orbit failures. At that altitude each satellite covers a circular area of 4,700 km (2,900 miles) and is in-view to a location on the ground for approximately 9 minutes. Using a small amount of overlap in coverage between each satellite, the Iridium network hands-off the call to the next satellite coming into view to the ground location. This is similar to a GSM cellular telephone system where the subscriber moves from one cell site to another except that the satellite is the moving vehicle. The speed of the aircraft appears almost stationary compared to the speed the satellite moves.
Iridium operates in low earth orbit, which means it doesn't cost as much to get their satellites in space. The cost to install on an aircraft is also relatively cheap compared to earlier systems.
[ICAO SVGM, ¶2.4]
- The Inmarsat network of satellites is in geostationary orbit directly above the earth equator at an altitude of 35,786 km (22,236 miles). At that altitude above earth, each satellite's footprint covers approximately 120 degrees of the earth at the equator and to approximately 82 degrees North and 82 degrees South latitude. The orbital period of each satellite is exactly the same as the rotation period of earth so each satellite appears to remain in the same position. Inmarsat periodically renews its satellite constellations and operates both I-3 and I-4 generation satellites.
- There are three new I-4 (Alphasat will become the 4th I-4) and four I-3 satellites providing aviation services, to include PSTN-based voice. L-band frequencies allocated for aviation AMS(R)S are split between a transmit and receive block. This allows the subscriber unit using a frequency duplexer to receive and transmit simultaneously. Inmarsat's primary transmit frequency allocation is adjacent to Iridium's allocation used for both transmit and receive; this can cause interference to the secondary Iridium receive allocation when the aircraft operator desires both satellite services to operate simultaneously and on the same aircraft.
- SwiftBroadband (SBB) is the next Safety Services technology to be introduced after Classic Aero. SBB is only available on the Inmarsat I-4 satellites providing such services as PSTN voice, but will also introduce new capabilities to properly equipped aircraft.
Public Switched Telephone Network (PSTN)
[ICAO SVGM, ¶2.6] The aeronautical SATVOICE system uses the public switched telephone network (PSTN) and/or dedicated networks to route calls between the aircraft and the appropriate ground party. Dedicated network access switches locate the aircraft anywhere in the world regardless of the satellite and ground earth station (GES) to which the aircraft is logged on.
There is a fair amount of magic going on here, but all of that was handled by the vendor who installed the equipment on your aircraft, the satellite service provider, and the person who set up your aircraft accounts. From the pilot's perspective, it is only important to remember that when you pick up the phone and the necessary connections are made, you are talking to someone on the other end who picked up a telephone. You cannot do this as a matter of making normal position reports and other air traffic services unless the air traffic services unit on the other end has made provisions to use these SATVOICE systems.
SATVOICE as a Long Range Communications System
Is SATVOICE a valid Long Range Communications System (LRCS)?
[ICAO SVGM, ¶2.1.4] SATVOICE could potentially be considered a LRCS as defined by State MMEL/MEL policies. When approving reduced carriage requirements for HF radio, States may allow aircraft to operate with only one serviceable HF radio. However, airspace requirements will take precedence over the MMEL/MEL requirements.
The answer is "It depends." It depends if your state and the airspace in which you fly allow it. If you are flying an N-numbered airplane your state does allow it, but it is more complicated than that.
Can SATVOICE replace the HF?
[ICAO SVGM, ¶2.1.4] SATVOICE is not a replacement for ADS-C/CPDLC or HF/VHF voice via a radio operator.
LRCS to be Carried on Board
[ICAO SVGM, ¶3.3.2]
- The State of the Operator and/or State of Registry establish the minimum number of LRCSs to be carried on board. In principle, where two LRCSs are required, one SATVOICE system and one HF voice system could be approved for flight operations where both services are available for routine communications, as follows:
- An HF radio is considered to be LRCS; and
- Other (e.g. SATVOICE) two-way radio equipment may be used if allowed by the relevant airspace procedures.
Note 1.— EASA is considering rules and means of compliance that would allow for one SATVOICE system and one HF communication system, providing that said services are available for routine communications.
Note 2.— The FAA Policy Letter (PL)-106 provides MMEL relief that allows one HF communication system, if the SATVOICE system is approved as a LRCS.
The referenced policy letter introduces a "global change" to all existing MMEL documents, discussed below.
Note.— For example, the State of Design is the FAA for the United States and EASA for European Union States.
Note.— For example, see rule OPS 1.030 in the EU.
- The regulations now address long-range communication requirements in terms of LRCS. With that as a basis, an aircraft on extended range segments unable to utilize line-of-sight systems must have at least two operational LRCSs to honor regulatory communication requirements (unless specifically excepted under the operational rules).
- While CPDLC enhances ATS communications for normal use, it is not adequate for non-routine and emergency communications and therefore not appropriate as a basis for MMEL relief of HF communication systems (ref. FAA Legal Interpretation dated 06 Dec 2011 regarding 14 CFR § 121.99 data/com in lieu of voice requirements). In addition, some ATS facility may not be capable of providing SATVOICE services as a LRCS. HF-voice is the only LRCS currently available for Air Traffic Control communications in many areas. Therefore, in areas requiring two operational LRCSs, at least one must be HF-voice when the MEL is applied. In areas requiring one LRCS, that system must be HF-voice.
Figure: FAA LRCS MMEL Policy, from FAA MMEL Policy Letter (PL)106, page 3.
This is the first document from the FAA that says you need two LRCS. You could get away with just one HF as your only means of long range communications until this came out. Now, if you don't have a qualified SATVOICE or CPDLC, you need two HFs.
Flight Crew Procedures
[ICAO SVGM, ¶5.1]
- An aircraft operator with data link equipped aircraft (CPDLC, ADS-C, and FMC WPR) operating in airspace where data link services are provided should use data link as the normal means of communications. Some normal ATC communications and most non-normal communications will require use of voice communications. The flight crew may use SATVOICE or HF/VHF voice at their discretion, provided the use is in accordance with airspace requirements established by Regional SUPPs, AIPs (or equivalent publication) for the flight.
- Although the underlying technology lends itself to a conversational mode of communications, such use can create misunderstanding and confusion. Therefore, when using SATVOICE, the flight crew should follow RTF conventions identical to HF/VHF communications in accordance with applicable standards and regulations pertaining to aeronautical communications.
- When SATVOICE is required for the flight, such as for extended operations or to meet airspace communication requirements, then during pre-flight or prior to entry into the relevant airspace, the flight crew should ensure the aircraft SATVOICE system is operational and there are no notifications of SATVOICE service outage in that airspace.
- On initial contact with a radio station, the flight crew should provide aircraft identification and request frequency assignment and perform a successful SELCAL check on HF, when required by the appropriate ATS authority. Subsequent communications with that radio station may then be performed via SATVOICE or HF/VHF voice, in accordance with applicable airworthiness, operating and airspace requirements.
- The SATVOICE numbers (e.g. short codes) for aeronautical stations and ATSUs are published in State AIPs and some charts. SATVOICE numbers together with the appropriate priority level may be stored in an aircraft SATVOICE system for easy access by the flight crew.
Example Aircraft SATVOICE LRCS Discussion
You cannot assume a satellite telephone installed in your aircraft qualifies as a suitable LRCS that can take the place of one HF. The satellite telephone must pass several security and Required Communications Performance (RCP) tests. The easiest way for you, the pilot, to tell if your system qualifies is to check your MMEL. The GV series MMEL, for example, was modified as a result as follows:
Figure: GV MMEL HF Systems, from GV MMEL, page 23-14.
Gulfstream has stated SATCOM Voice or Data Link can substitute as a backup to normal HF communications, so with this series of aircraft we are good to go.
What if you don't have such a statement in your MEL?
Figure: DA-2000 MMEL HF Systems, from DA-2000 MMEL, page 1-23-1.
This is an older copy of the DA-2000 MMEL for sake of illustration, they might have a qualified system and this may have changed. But for the purpose of this discussion, if what you see is something that doesn't mention your satellite phone system or an LRCS at all, you might not have a qualified system. You should ask your aircraft manufacturer for guidance. If they are clueless, send them the Appendices to the ICAO Satellite Voice Guidance Material, available for download below.
ARINC SATCOM Voice Procedures
[ARINC Handbook, ¶2.6]
- ARINC Communications Centers are equipped to receive and originate SATCOM Voice calls from or to suitably equipped aircraft. It is recognized that these systems, due to cost and other requirements, are still not available to a large number of aircraft; however, ARINC has the capability to use SATCOM Voice as an alternative means of communications for either ATC or AOC communications with those aircraft that have been equipped. The medium used for communications is transparent to the end user. All ARINC services using HF/VHF are available, and SATCOM Voice messages either can be relayed by the ARINC Radio Operator or the call-in progress can be connected to other phone lines (conferenced) through the telephone control system at each ARINC Communications Center.
- Note: When using SATCOM voice, continue to use radio discipline procedures. Using the SATCOM phone like a regular telephone can cause misunderstandings and confusion.
- Satellite Voice-equipped aircraft should direct calls to the appropriate ARINC Communications Center using either INMARSAT-assigned security phone numbers (ICAO short codes) or direct dial using the 10-digit PSTN phone number:
- Note: These six-digit numbers are converted by the Ground Earth Station (GES) receiving the aircraft call announcement to the respective PSTN dial number for connection to the appropriate ARINC Center. This only works on the INMARSAT satellite system.
- After an answer by the ARINC Radio Operator, the parties should complete the exchange of information using the same procedures as would be used on other voice (HF/VHF) communications mediums.
ARINC says the use of SATCOM is "transparent" to the end user, meaning ATC. Many of the ATC sources say you should use SATCOM in lieu of HF or CPDLC only in unusual circumstances.
The phone call ends up with the HF radio operator who is expecting you to use the same terminology as if on HF.
More about this: Voice Position Reports.
|Pacific Flights||Atlantic Flights|
|SFO 436625||NYC 436623|
You will be using INMARSAT satellites but your aircraft may or may not have an INMARSAT phone. To use the short codes you need an INMARSAT phone.
Data Link on VHF vs. SATCOM
[G450 Aircraft Operating Manual, §2B-21-40, ¶1.B.] By default, the PLANEVIEW CMF communicates by way of the land-based ACARS VHF network, which includes the Aeronautical Radio, Inc. (ARINC) and SITA subnetworks. Based on position information provided by the aircraft FMSs, the CMF automatically tunes to the appropriate subnetwork. In areas where VHF coverage is unavailable, the CMF may use the Inmarsat Aero-H, Aero-H+, or Aero-I satellite UHF networks. This provides both packet mode (datalink) and circuit mode (voice and data) capabilities to the aircraft. The CMF switches to and from the satellite UHF network based on the availability of land-based VHF network coverage.
The G450, as an example, automatically switches to SATCOM for data link when VHF coverage is unavailable.
Line of Sight and Curvature of the Earth Issues
Figure: INMARSAT Line of Sight, from Eddie's Notes.
[G450 Aircraft Operating Manual, §2B-21-40, ¶1.D.]
- All PLANEVIEW CMF transmissions, whether VHF or satellite, require line of sight to a VHF ground station or Inmarsat satellite, respectively.
- Transmitting by way of satellite while on the ground is generally reliable. Although, line of sight issues may still arise due to surrounding terrain and man made structures because the Inmarsat satellites are in an equatorial geostationary orbit. In flight, the curvature of the Earth is a concern only at latitudes greater than 70° North or South. Except at these high latitudes, satellite coverage while in flight is seamless.
Because INMARSAT satellites are in geostationary orbits over the equator, the curvature of the earth limits their use at the poles. While the G450 manual says you may have issues above 70° latitude, it is said that SATCOM is available for voice and data link up to 82°N.
[G450 Aircraft Operating Manual, §2B-22-30] The airborne SATCOM equipment links to one of the geostationary International Maritime Satellite Organization (INMARSAT) satellites, which in turn links to a ground earth station. The ground earth station then connects to a long distance telephone company, and then to a local telephone company. Once these connections are established, the airborne communication equipment communicates with the ground based equipment using the telephone company services.
Portions of this page can be found in the book International Flight Operations, Part IV, Chapter 4.
14 CFR 1, Title 14: Aeronautics and Space, Definitions and Abbreviations, Federal Aviation Administration, Department of Transportation
ARINC Voice Services Operating Procedures Handbook, ARINC, Annapolis, MD, 13393 Rev. R, September 27, 2006
FAA MMEL Policy Letter (PL)106, Revision 5 GC, June 6, 2014
Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.
Gulfstream GV Master Minimum Equipment List (MMEL), GV GV-SP (G550), GV-SP (G500), GIV-X (G450), GIV-X (G350), Revision 8, 11/07/2014