Development of Wireless Avionics Intra-Communications

While avionics engineers, producers and installers busy themselves with ADS-B mandate activity, it might be an extra burden for them to focus on new developments in the industry. One is the recent migration of wireless avionics intra-communication (WAIC) technology into aircraft platforms.

WAIC is a potential means of reducing aircraft wiring by 30%, using wireless devices to communicate data, on radio frequencies and in place of wiring, between aircraft systems that function for safety and regularity of flight. (Such devices do not include those used for air-to-ground, air-to-satellite, air-to-air or in-flight entertainment purposes.)

Initially, WAIC required classification to be followed by the purposeful direction of a committee tailoring it, specifically, into an avionics standard. Because WAIC involves the use of radio frequencies that may be used by others, classification of WAIC had to commence with activity under the International Telecommunications Union – Radiocommunications Sector (ITU-R). Also, because WAIC frequencies are originating from aircraft that are transient, by crossing international boundaries, it required the collaboration of both ITU and the International Civil Aviation Org. (ICAO) in an overall classification effort.

The ITU ensures harmonized access to electromagnetic frequencies, worldwide. The ICAO, similarly, ensures harmonized standards and operations for aviation. The classification of WAIC originally focused on low and high data rates as well as location-related aspects, either inside or outside the aircraft. For the WAIC operating frequency spectrum, ITU initially commenced with the assumed range of 2 to 5 GHz. The 2011 report from the ITU-R was issued as an M document, covering the “mobile, radio-determination, amateur and related satellite services,” and issued as M.2197.

Since 2008, another group has played a major role in the overall development, classification and standardization of WAIC. The Aerospace Vehicle Systems Institute (AVSI), a cooperative of companies, academia and government agencies, centered on the Texas A&M University campus, has nurtured and promoted the WAIC concept with heavyweight aviation giants deeply engaged. Current members, beyond the university’s Engineering Experiment Station, include Boeing, Airbus, Embraer, Harco, Honeywell and United Technologies. BAE, Gulfstream and Bombardier also have played a significant role earlier in the institute’s WAIC work.

After the release of the ITU-R report, AVSI requested that the organization evaluate specific frequency bands within the 2- to 5-GHz range. Covered under Report M.2318.0, ITU evaluated the frequency bands 2,700 to 2,900 MHz, 4,200 to 4,400 MHz and 5,350 to 5,460 MHz.

The only frequency band below 15.7 GHz found to be suitable for WAIC and that would not cause or be subject to interference, was the 4.2 to 4.4 GHz band. But there was the issue of onboard radio (radar) altimeters also operating within the same frequency spectrum.

Knowing that the 4.2 to 4.4 GHz band was the right band for WAIC, AVSI and others worked toward a worldwide adoption that was finally announced at the 2015 World Radio Conference. This also meant that the FAA (RTCA), EASA (EUROCAE) and ICAO would all rally behind the assigned frequency and build on the ITU-R reports to develop standards. They would also seek to resolve the co-habitation of both WAIC and radio altimetry operating in the same band. Devices will be low (10 mW) or high (50 mW) power rated and expected to be positioned less than 330 ft (100 m) from each other.

Developing the Standard

AVSI was instrumental in the formation of a special committee and working group tasked with developing WAIC standards that will guide designers, engineers and installers in the production and integration of WAIC applications. Each consensus-based panel of experts is fully supported by the ICAO, ensuring spectrum usage falls within ICAO convention guidelines to obtain benefits for equipment certification. The two panels include RTCA SC-236 and EUROCAE WG-96.

The RTCA request is given in the form of formal tasking from the FAA, which leads to a terms of reference document. The document, issued in June 2016, calls for the development of a Minimum Operational Performance Standard (MOPS) to allow WAIC devices to operate safely alongside radar altimeters. The RTCA defines MOPS as a system that “provides the information needed to understand the rationale for equipment characteristics and requirements stated, describe typical equipment applications and operational goals, and establish the basis for required performance under the standard.” SC-236, working jointly with WG-96, is to develop the standard for operational safety communications systems onboard an aircraft to include engines, APU and landing gear.

Meanwhile, WG-96 for Europe has been developing a process specification to define compliance methods for safety demonstration of systems using WAIC. Though a joint effort, WG-96 will release a EUROCAE version of the same MOPS, both planned for a 2019 completion.

There are two primary MOPS requirements. One is that the safe operation of radio altimeters is not compromised. The other is allowing the worst-case performance of a WAIC application to be pre-determined.

These are further divided into the following subset of requirements: coexistence of WAIC components and radio altimeters on board the same aircraft; coexistence of WAIC components and radio altimeters on board different aircraft; coexistence of WAIC components on board the same aircraft; and coexistence of WAIC components on board one aircraft with WAIC components on board other aircraft.

Due to the proximity of flights when using new performance-based navigation procedures, it is possible for aircraft to be flying within a closer distance from each other, creating a greater risk for WAIC interference. Specifically, with respect to radio altimeters, aircraft flying in close proximity, above or below each other as opposed to side by side, may be more prone to interference. This is because the radio altimeter antenna is mounted on the aircraft’s lower fuselage.

The ICAO requires that any susceptibility of interference between different aircraft is evaluated, so there will be a WAIC standard and recommended practice developed to ensure coexistence between aircraft.

Additionally, the terms of reference document addresses possible cybersecurity concerns and links SC-236 activity to SC-216, the RTCA Aeronautical Systems Security Committee.

Why WAIC

Aviators are always looking for ways to reduce aircraft weight, to increase performance, for runway access and to use less fuel. Aside from contributing to these desires, WAIC technology improves aircraft safety and efficiency by removing electrical wiring between aircraft systems.

Notably, today’s typical aviation department relies more on real-time downlinked performance and fault data from the aircraft. This increases the need for system sensors able to communicate the data to a central monitoring computer for transfer via satellite to the ground. Traditionally, this involves more wiring and therefore serves a greater need for high data capacity, safety-related wireless communication between aircraft systems.

Of significance is the ability of WAIC to inform on the status of aircraft moving parts and the monitoring of reliability impact elements, such as temperature, pressure, humidity and wear status. Future applications not able to be served by using wires alone, may be supplanted or supplemented by WAIC devices.

As risks are revealed, via function hazard and common mode failure analysis and lessened through the reduction of wiring, it is planned that double and triple system redundancy may also be mitigated in the future.

WAIC promotes the ability to reconfigure systems for upgrades or during integration for new product features. If these changes can be accomplished by wireless reconfiguration, as opposed to wiring amendments, the advantage of having less touch points will be clear.

Because the WAIC standard will exist and be provided as guidance for the certification authorities and the industry alike, it should mean a less cumbersome process for the certification of equipment and especially for aircraft integration. Designers and certification engineers might apply a similar process as that applied to radio devices used in navigation, surveillance and communication systems.

Because of the WRC-15 frequency allocation, the equipment-licensing process may be applied globally, providing a harmonization of the technical and operational criteria.

This same harmonization applies to safety guidance material and design assurance guidance used to certify WAIC equipment.

Wiring reduction

The argument for wire reduction is validated when a typical dual-aisle air carrier aircraft is reviewed. For an approximated total wire count of 100,000 and a total length of 292 miles (470 km), the weight of wire incorporated into the aircraft’s total weight is 12,566 lbs (5,700 kg) — a typical light aircraft weight limit. The wiring must be attached along its route, so add about 4,189 lbs (1,900 kg), or 30% more, and this does not include all the connectors at the termination at either end. Assume a single-aisle air carrier aircraft to be around 50% of both.

Of course, WAIC devices will not eliminate all wiring, but it has been estimated to potentially reduce the total by 30%, irrespective of the aircraft size.

In fact, WAIC devices may supplement aircraft wiring to achieve its reduction. This is because for safety-critical systems, there should be two separated wires for each function and yet, being wires, both may have the same modal failure criteria. If one were replaced using wireless radio communication then the safety-analysis outcome would be very different.

For spectrum bandwidth requirements, the sensors are first grouped by high and low data rates, then totaled together for anticipated overall data usage. Some estimates of total WAIC data needs are placed at 145 MHz of spectrum allocation, for each dual-aisle air carrier aircraft.

As of September 2017, the SC-236 (WG-96) had received a thorough briefing of the WAIC requirement, the certification authority request and global context.

Also, the committee has been familiarized with MOPS, which will eventually lead to a DO-XXX document. Europe will further issue a draft ED 246 document for wireless onboard avionics network, which has already been open for comment.

The final MOPS may even be used as a basis for an FAA technical standard order (TSO) and a Europe ETSO, as applies to the design and approval of aircraft-related equipment. Equipment with TSO design approval will be eligible for use on FAA type-certificated aircraft.

Furthermore, the FAA could later issue an advisory circular and EASA a certification memo, both addressing the WAIC certification process.

As the work of SC-236 (WG-96) progresses, the scope and depth of required activity unfolds. By examining some of the public activity, it is possible to obtain a glimpse at the status and inner workings of WAIC standards development.

The MOPS breakdown will follow a standard format and, from a technical perspective, include the following major areas: equipment performance standard and environmental conditions; test procedures; manufacturer conditions; and operational performance characteristics.

In preparation for MOPS, the activity includes an understanding and development of industry guidance covering, at a minimum the following:

• The WAIC freqnecy spectrum requirements.

• High & Low/ Inside & Outside (the aircraft), date rates.
• The WAIC model.
• Radio altimeter protection via use of directional external WAIC device antennas.
• Security and encryption.
• Some of the important criteria for the physical equipment includes:
• Determination of both digital and analog bus sensor component.
• Power sources and requirements.
• Guidelines and contraints for the installation
• Antenna considerations, including location, orientation and field patterns.
• Maintenance of WAIC applications, including continued airworthiness.
• Retrofit and reconfiguration aspects.
• WAIC radio as wireless sensors.
• Radio frequency human protection.
• Applicability of other standards documents, particularly universally applied standards such as DO160G-Environmental, DO 254-Hardware & DO 178C-Software.
• One activity has been flight testing to check for the susceptibility of WAIC-like emission interference on radio altimeter frequencies, as recently conducted through a coordinated effort by NASA, Honeywell, Thales and Rockwell Collins.
• NASA also conducted a funded modeling research program, and in December 2016, it released a white paper covering reflective characteristics of WAIC emissions within aircraft cavities as well as a deployed/stowed nose landing gear.
• AVSI is a primary facilitator, arranging several tests and providing background or required data, to validate the developing standards.
• Aircraft outfitted with operational WAIC devices will fly further, longer, cheaper and greener than their fully wired counterparts. The industry can see the clear advantages of wireless safety communication. Aircraft builders and completion facilities have a whole new business sector to add to their portfolios, and if not incorporated at assembly, WAIC applications would be installed during major events or system upgrades.
• AVSI, RTCA SC-236 and EUROCAE WG-96 are diligently working with their industry partners on producing usable standards within the next three years, while the ICAO continues to ensure its global reach and harmonization. AVS

Some of the important criteria for the physical equipment includes:

One activity has been flight testing to check for the susceptibility of WAIC-like emission interference on radio altimeter frequencies, as recently conducted through a coordinated effort by NASA, Honeywell, Thales and Rockwell Collins.

NASA also conducted a funded modeling research program, and in December 2016, it released a white paper covering reflective characteristics of WAIC emissions within aircraft cavities as well as a deployed/stowed nose landing gear.

AVSI is a primary facilitator, arranging several tests and providing background or required data, to validate the developing standards.

Aircraft outfitted with operational WAIC devices will fly further, longer, cheaper and greener than their fully wired counterparts. The industry can see the clear advantages of wireless safety communication. Aircraft builders and completion facilities have a whole new business sector to add to their portfolios, and if not incorporated at assembly, WAIC applications would be installed during major events or system upgrades.

AVSI, RTCA SC-236 and EUROCAE WG-96 are diligently working with their industry partners on producing usable standards within the next three years, while the ICAO continues to ensure its global reach and harmonization.