Article

DEFINING ‘WHAT IS’ AND ‘WHAT COULD BE’ IN AEROSPACE

September 11, 2019

DEFINING ‘WHAT IS’ AND ‘WHAT COULD BE’ IN AEROSPACE

Mike McConnell 

SATVOICE is becoming more than a passing interest to airlines and inching closer to a real requirement in Part 121 operations. Some data suggests that it may have a wider adoption in Business and General Aviation due to simply checking the Optional Equipment box in large cabin class aircraft and how it marginally impacts the Total Costs of Ownership (TCO). When dissecting an industry conversation on SATVOICE, most of the discussions surrounding 2014 published AC20-150B where the FAA outlines the ways a SATCOM receiver with voice capability can replace a Long Range (LRCS) radio (HF) on the MMEL. But there are other reasons to add VOICE capabilities to existing satellite installations for a fraction of the expected costs.  

Since 2013, Iridium's Air Traffic Service ("ATS") Safety Voice has provided an alternative to HF radio waves, the current means of cockpit communications to Air Traffic Control ("ATC"). Contrary to their name, HF radio waves operate on a much lower frequency than the L-band, at .003 - .03 GHz. SATVOICE has proved to be cheaper for airliners to use because, not only is the wave travel distance reduced, but installation cost, antenna size, and service rates all decrease as well. The best-in-class HF radio operates at speeds of 1,800 baud, or 1.8 kbps, compared to Iridium's 2,400 kbps. But the Holy Grail of reasons to install SATVOICE for the airlines is the weight savings – approximately 40 lbs of net weight reduction by removing one of the HF’s coupler’s and one receiver/transmitter and then installing the SATCOM with SATVOICE.

The next frontier in SATVOICE will come from Iridium’s new NEXT constellation. Because NEXT consists of 66 satellites in a Low Earth Orbit ("LEO") constellation, as opposed to a Geostationary Orbit ("GEO"), used by Inmarsat, Iridium NEXT provides the lowest latency and best-in-class speeds. GEO satellites can cover more ground than LEO satellites, located 22,300 miles above a fixed point on the equator. However, the curvature of the earth limits its use at the poles. It is unknown when NEXT will be approved for SATVOICE, but if history is a guide, Iridium has already submitted the start of necessary FAA approvals, and it should be approved within 12 months of constellation activation.

As a general rule of thumb, upgrading a current Iridium satellite installation to an Iridium NEXT receiver and antenna which has the same form factor and fit to the fuselage mounting plate should be a <20% upgrade path over the original Iridium installation.

Iridium's current satellites reside just 431 miles above the ground in a polar LEO at 16,689 mph. While some aircraft flight manuals say you may have issues above 70° latitude, most say that INMARSAT SATCOM is available for SATVOICE and datalink up to 82°N. Therefore, Iridium has no such polar limitations for SATVOICE and data transmissions.

In terms of VHF and SATVOICE compatibility for data link, the ACARS Communication Management Unit (CMU) utilizes an automatic switching function. This is in Accordance with ARINC Specification 619, which addresses message priority and media selection, 1 Gatelink, 2 VHF, 3 SATCOM, and 4 HF. The CMU automatically selects the available communications medium based on the ranking shown above. If a communication link is not installed, inoperative, out of communication with the ground link, CMU will go to the next available communications link. If a higher priority communications link comes back into communication with the ground link, CMU will automatically switch to that link. The operator does not have any control over this switching.   All current Boeing and Airbus, as well as business jets from the last 15 years, have this switching function per ARINC 619. If the CMU has GEO Positioning active, it will automatically tune to the appropriate ARINC or SITA subnetwork based on position information provided by the Global Position System input to the CMU.

In areas where VHF coverage could be unavailable, as on the polar routes, an operator could use the Iridium network, or in the Indian Ocean, an aircraft could use the Iridium, Inmarsat Aero-H, Aero-H+, or Aero-I satellite UHF networks. This provides both packet mode (datalink) and circuit mode (SATVOICE) capabilities to the aircraft. The CMU switches to and from the satellite network based on the availability of land-based VHF network coverage.

The real benefit that most people know about is when you can remove an LRCS HF radio on the MMEL.  The FAA Advisory Circular addresses the approval for removing the HF radio equipment when equipped with Iridium SATVOICE equipment with Safety Services approval.

But enough of this Electrical Engineering class. Will anyone buy SATVOICE? If it works every time, is priced right, and these benefits are crystal clear, yes, airlines will adopt it as a standard.

L2 currently has 7 SATCOM FAA STCs for Iridium and Inmarsat products installed on both Boeing and Airbus aircraft and is working on more for airline operators. Six of the STCs include SATVOICE Safety Voice capability. That experience suggests the company is a “Go-To” resource for data, engineering, certification, and installation of SATCOM products. 

SATVOICE is becoming more and more interesting for airlines as a requirement. With this natural technology evolution, SATVOICE should become more and more prevalent in airliner cockpits. Increasing the adoption of SATVOICE is becoming not an IF but a WHEN and that WHEN could be 2020.