The commercial Aircraft Communication, Addressing and Reporting System (ACARS) is like the digital heartbeat of the commercially operated air transport airframe. Since the inception of the original ARINC ACARS data link network more than 30 years ago (now managed by Rockwell Collins Information Management Systems), it has continually evolved as a character-based messaging service using ARINC 618-based air-to-ground protocols to link aircraft onboard systems with either the Rockwell Collins or SITA-operated ACARS networks.
According to ARINC Industry Activities Ku/Ka Band Subcommittee Chairman Peter Lemme, the industry is achieving Internet Protocol (IP) networking today by leaving the historical structure of ACARS in place, while using an ACARS aircraft gateway to take the self synchronizing ARINC 429 avionics data transfer standard and interfacing that to Internet Protocol, and then using IP to deliver the specified message to the Datalink Service Provider (DSP). Industry has already achieved this capability using Iridium’s Short Burst Data (SBD) network transport capability designed for transmitting short data messages between functional equipment and centralized host computer systems. The other new method for operating ACARS over IP, is Inmarsat’s SwiftBroadband Safety service.
In 2015, Hawaiian Airlines became the first carrier to fly commercial revenue flights using the ACARS data service network with an ARINC 429 interface, communicating messages using IP, enabled by the Cobham Satcom Aviator 300 Level D Intermediate Gain Antenna (IGA) and Inmarsat’s SwiftBroadband for Safety Services network.
Dan Smith, principal avionics engineer at Hawaiian Airlines, is quick to point out that their use of the Cobham Aviator 300 Level D to do this is not a trial, but is actually being operated on commercial flights. “On our 767 we have the Cobham Aviator 300, and the corporate purpose of that is to support our Electronic Flight Bag (EFB). The industry purpose for using that is [Future Air Navigation System] FANS over SwiftBroadband (SBB), or safety services over SwiftBroadband. We get about 190 kilobits per second, and this is SBB over the prioritized IP channel, where everything is packaged up on the Aviator, sent down and unpacked on the ground, and sent over. In our case, ARINC unpacked in their station and then routed to where we’ve directed the information to go,” says Smith. Effectively, what Cobham and Inmarsat are doing for Hawaiian is to put an IP bridge between the aircraft’s ACARS transmissions to the SITA and Rockwell Collins-operated ground-based networks, because it provides a much faster and less expensive transmission protocol.
Hawaiian also seeks to use what Smith calls the “background IP” for their EFBs. However, due to security concerns associated with the Aircraft Interface Device (AID) that they are currently using, as it has not yet achieved a Design Assurance Level (DAL) level D certification.
“We’re not unique in that we seek to minimize ACARS traffic because it’s very expensive. Just do the math: If you’re paying on the order of 4 cents a kilobit on the ground, and 10 cents a kilobit in the air, you can figure out what the cost per megabyte is, and the cost per gigabyte. It’s astronomical. In fact, satcom ACARS is cheaper than VHF ACARS in the far East. In that region, destinations we fly to such as New Zealand, Australia, China and Japan, are charging 45 cents per kilobit for VHF ACARS. We’re talking $1,000 per megabyte. What we’ve done is turned off VHF ACARS in the Far East. On our A330s, for example, in Japan and China we send everything over satcom,” says Smith.
At a government-industry meeting in Washington D.C., in August, the FAA’s Performance-based Operations Aviation Rulemaking Committee Communications Working Group (PARC CWG) will go through Hawaiian’s operation, message by message, and effectively determine the widespread viability of approving the use of ACARS over IP for more airlines going forward. The PARC CWG goal in evaluating the Hawaiian operation is specifically designed to investigate the performance of FANS 1/A Controller to Pilot Data Link Communications (CPDLC) and Automatic Dependent Surveillance-Contract (ADS-C) over SBB. This investigation includes an operational evaluation within the Performance-Based Communication and Surveillance (PBCS) framework and against Required Communication Performance (RCP) 240 and Required Surveillance Performance (RSP) 180 specifications.
Andy Beers, director of aeronautical sales at Cobham Satcom, says that while Hawaiian is flying commercially using Aviator 300 to enable ACARS over SwiftBroadband-powered IP, Hawaiian is using a version of their hardware, the Aviator 300 level D, that will not be made commercially available and is only being used because their future facing product, Aviator S, was not yet ready for installation on Hawaiian’s fleet.
“Aviator 300 D was installed in the 767 fleet, it’s a class 7 SBB terminal with the addition of an ACARS gateway, and we have configured the software installed on the Aviator 300 system to convert the ACARS messages to IP data and vice versa, a similar gateway for ACARS service, complete end to end ACARS over IP link so there’s a ground gateway as well. Cobham is in the process of developing a completely new range of SBB systems called Aviator S, this will do everything the 300 is doing for the evaluation but it will also allow for non ACARS IP services, so an IP link in the cockpit for things like EFB connectivity and you’ll be able to do safety and non-safety data over the same channel,” says Beers.
Cobham obtained a Supplemental Type Certificate (STC) for this installation and approval of the operation through L2 Aviation consulting services. According to L2 Aviation President and CEO Mark Lebovitz, the ACARS over SBB STC was governed by RTCA standard DO-262B, which is the minimum operational performance standard (MOPS) for avionics supporting Next Generation Satellite Systems (NGSS).
“The scope of DO‑262B includes SBB equipment. The FAA is planning to update AC 20-140B to include the use of SBB equipment for FANS 1/A CPDLC and ADS‑C,” says Lebovitz. “The L2 STC project involved modifications to aircraft systems allowing the use of SBB equipment for FANS 1/A CPDLC and ADS-C, as well as satellite voice communications, for use by the flight crew. The STC project was completed via an FAA Issue Paper process as the update of AC 20-140B to include SBB was (and is) in work.”
Since there was no sub-network indicator and relevant previous criteria to provide a baseline for evaluating SwiftBroadband as a viable sub-network for FANS 1/A+ or FANS 1/A, the L2 team used FAA Technical Standard Order (TSO)-C159b, which refers to RTCA DO‑262B, Appendix E, Section 2.4, as a basis for evaluating the SBB equipment, which includes the SBB transceiver, Diplexer/Low Noise Amplifier (DLNA) and antenna, Lebovitz says.
“For interoperability, we used ARINC 618-7, Air/Ground Character-Oriented Protocol Specification, which is common between Classic Aero and SBB, and ARINC 781-5, Mark 3 Aviation Satellite Communication Systems, which includes SBB and other services that operate in L-band,” says Lebovitz.
There are also cybersecurity concerns associated with introducing IP into any aircraft cockpit, Lebovitz says. Specifically, the internal risks associated with authorized users on the network accessing systems and information that are flight critical and could cause problems with the operation of the aircraft. The methodology for reducing or eliminating this risk is by isolation of the new system from critical aircraft systems. This may be done by physical isolation or through domain control where the new system is not connected to the more critical Aircraft Control Domain (ACD) and only interfaces with the Aircraft Information Services (AIS) or Passenger Services Domains (PSD), the L2 chief says.
One of the aspects of managing the ACARS aviation network pointed out by Philip Clinch, vice president of aircraft solutions for SITA, is that the ACARS system includes multiples layers and to move ACARS messages over a new IP generation link. All of the stakeholders involved have to figure out which layer to put over the new link. ACARS has two main layers: one being the core messaging ARINC 620 layer and the other being the lower layer air to ground link, Clinch says.
Dan Pendergast, senior director of Information Services International, the division of Rockwell Collins that operates as the world’s other ACARS Datalink Service Provider (DSP) — outside of SITA — says that as airlines add or adapt new protocols, they monitor and integrate those new protocols, such as IP, into their baseline network.
“SBB is a broadband link and interest from our customers is to enable cockpit applications that need more bandwidth than the classic legacy links. However, a significant portion of their
business is still using the traditional ACARS protocol so we have a new link and as a service provider we implement that new link, so that over the same link we can move legacy ACARS data and IP-based data. [We offer] legacy data to support cockpit safety services and ACARS applications and IP data to enable our customers who want to do high bandwidth applications such as supporting a tablet or an EFB,” says Pendergast.
What does the future look like for using IP as a cost-effective method for sending ACARS information? The ACARS network itself is not going anywhere. Based on what Hawaiian is doing, and what the PARC CWG is approving, ACARS will continue operating in the way that Hawaiian is using it, by linking in a new protocol to the ARINC 429 interface used by an end system — such as a Flight Management System (FMS) — to an ACARS gateway, encapsulating the ACARS message within that protocol, and then sending it to Rockwell Collins or SITA to then distribute it with ground-to-ground protocols.
“SITA and ARINC have provided a valuable service, but times are changing, and the volume of data created by modern aircraft is orders of magnitude, 100 times maybe even a thousand times more data than older aircraft. Even at 1 cent a kilobit, SITA and ARINC may make a lot of money in the short term but in the long run it is unsustainable,” says Smith.
Furthermore, SITA and Rockwell Collins are actively working with different protocols, as previously mentioned by Pendergast.
“One of the interesting things is that SITA is currently a reseller of our ACARS over IP solution. They are a reseller of that solution and they’re actively using the ACARS over IP technology in trying to move as much of the traffic that Airline Operational Communication (AOC) traffic off the classic network the VHF the HF and the satcom don’t have HF, in order to make way for the new legislation about CPDLC safety services messages, the ATN network type stuff. So SITA can see very much, ACARS over IP as a key to offloading non-safety services messages,” says Murray Skelton, director of business development, Teledyne.
Recently, Cobham achieved a major Airbus contract win. The company was selected as a supplier of its Aviator 200 S and 700 S technology for the A320 and A330, confirming the viability of ACARS over IP as a widespread commercial aviation concept going forward. Global Market Forecasts released by Airbus and Boeing at the 2016 Farnborough Airshow project the A320 and 737 to be in the highest selling category of commercial air transport aircraft over the next 20 years. According to PARC CWG, Inmarsat expects SBB to perform similar to VHF and envisions that ICAO will be developing more stringent RCP/RSP specifications for new Air Traffic Management (ATM) operations, which could include domestic and oceanic/remote applications, where Classic Aero may not comply, but SBB could comply. An evaluation against more stringent Required Communication Performance/Required Surveillance Performance (RCP/RSP) specifications would be considered at a later time after ICAO develops new RCP/RSP specifications for the relevant ATM operations. “The future of ACARS as we see it, is that essentially only the really urgent information will go over ACARS and the rest will go over some type of prioritized IP channel,” says Smith. AVS