Weighing in on WAIC

Going wireless strives to detangle aircraft connection problems while enhancing efficiency and reliability.

Aircraft communications systems have traditionally included operational communications systems on board the aircraft, as well as sensors for engines, landing gear and proximity to nearby objects such as vehicles and other aircraft. These intra-aircraft communication systems have been largely dependent on complex wired connectivity and harness fabrication; a large commercial passenger aircraft has more than 100,000 wires. This results in increased aircraft weight (which increases fuel burn), inflexibility in cabin design and higher maintenance costs. Also, wiring is a significant source of field failures and maintenance costs. These systems have proven to be unreliable and difficult to reconfigure, and rely on double or even triple redundancy to mitigate the risk of cut or defective wiring.

WAIC systems are intended to support data, voice and video communications between systems on an aircraft to monitor different areas on the aircraft and to provide communications for the crew. Aerospace Vehicle Systems Institute image.

Wireless avionics intra-communication’s (WAIC) goal has been to detangle these problems. Designed to increase safety, WAIC systems are intended to support data, voice and video communications between systems on an aircraft to monitor different areas on the aircraft and to provide communications for the crew. With WAIC, wireless aircraft sensors at various points can wirelessly monitor the health of the aircraft structure and all of its critical systems, and communicate this information within the aircraft to those who can make the best use of such information. According to the Aerospace Vehicle Systems Institute (AVSI) WAIC is:

• Radio communication between two or more points on a single aircraft.

• Integrated wireless and/or installed components to the aircraft.

• Part of a closed, exclusive network required for operation of the aircraft.

• Only for safety-related applications.

• Based on short range radio technology (< 100 m). • Low-maximum transmit power levels of 10 mW for low rate and 50 mW for high-rate applications. • Mostly internal — within fuselage/cabin. WAIC can produce: • Less need for complex electrical wiring and harness fabrication. • Significant gain in re-configurability through improved installation flexibility. • Reliable monitoring of moving or rotating parts — such as landing gear, in which brake temperature and tire pressure are reported in real-time to the pilot. • Improved reliability of aircraft systems by mitigating common mode failures with route segregation and redundant radio links. WAIC does not provide off-board air-to-ground, air-to-satellite or air-to-air service. It does not provide communications for passengers or in-flight entertainment.

Approved and Protected

There is a protected worldwide spectrum frequency band for WAIC: 4.2-4.4 GHz (4200-4400 MHz). It was recommended by the International Telecommunication Union Radio Communication Sector (ITU-R) and has the challenge of catering to the massive communication needs of aircraft. This spectrum enables the technical harmonization of equipment across regions and countries.

Several major aviation groups expressed concern to FCC staff that there could be potential harmful interference to aviation systems operating in the 4.2-4.4 GHz band, which is next to the 3.7-4.2 GHz band, also known as the C-band. Because radio altimeter and WAIC systems operate in the 4.2-4.4 GHz band, “the uncompromised operation of both systems is essential to safety of flight,” the groups said in an ex parte filing.

AVSI helped form a special committee and working group tasked with developing WAIC standards that guided, produced and integrated WAIC applications. These experts ensured the spectrum usage fell within International Civil Aviation Org (ICAO) convention guidelines to obtain benefits for equipment certification. The two panels include RTCA SC-236 and EUROCAE WG-96. These are the two primary minimum operational performance standards (MOPS) requirements.

SC-236, Standards for Wireless Avionics Intra-Communication System (WAIC) within 4200-4400 MHz established MOPS for wireless equipment, allowing WAIC systems to share the radio spectrum with other aviation systems. Its goal was to facilitate procedural planning and decision-making for the FAA and the aviation community.

A large commercial passenger aircraft has more than 100,000 wires.

Under AVSI project AFE 76 — WAIC Protocols, detailed network and hardware architectures, protocols, requirements and appropriate protection criteria for spectrum sharing are being defined to protect WAIC and legacy altimeter systems from interfering with each other. WAIC applications have been categorized as either Low Rate (< 10 kbits/sec data transmit rate) or High Rate (>10 kbits/sec), each having some unique SWaP, cost, and performance requirements. AFE 76 now addresses more detailed design issues, including: system boundaries where WAIC standards might be applied; plans for WAIC spectrum assignments to ensure efficient usage; channel allocation and channel spacing scheme for WAIC systems; methods for achieving coexistence between WAIC systems installed on different aircraft; and a road map for working with international regulatory and standards organizations to ultimately implement WAIC components and systems.

WAIC’s radio frequency band 4.3-4.4 GHz is shared with radar altimeters where safety-critical wireless may operate. Work continues to be carried out to explore coexistence scenarios and interference avoidance techniques between WAIC and the radio altimeters. Experimental flight tests at NASA’s Armstrong Flight Research Center have been carried out in order to provide insight on WAIC coexistence and interference scenarios; the results of which will serve as a design tool for commercial wireless avionics development to abide by radio altimeter protection and coexistence criteria for the successful deployment of WAIC systems on aircraft.

EUROCAE WG-96 is a working group that developed a MOPS for a WAIC component that allows WAIC systems to safely coexist with radio altimeters in the frequency band 4200–4400 MHz. The MOPS will allow WAIC systems to share the band with radio altimeters and other WAIC systems in a way that (a) the safe operation of radio altimeters is not compromised and (b) allows the worst-case performance of a WAIC system to be pre-determined.

The WAIC project, conducted through AVSI, is a collaboration of major aerospace companies working together to address common issues associated with wireless avionics. The group achieved a worldwide radio frequency spectrum allocation for wireless avionics at the 2015 World Radiocommunication Conference (WRC-15). According to AVSI, this WRC-15 frequency allocation enables a globally applicable licensing process. It provides harmonization of the technical and operational conditions across regions and countries.

A Frequency Spectrum Management Panel (FSMP/3) held in September 2022 approved the draft WAIC SARPs, which will prevent interference between WAIC systems and radio altimeters in order to ensure the safe operation of aircraft. WAIC SARPs will be included in Chapter 4 of Annex 10, Volume V, under a new section 4.5 dealing with the frequency band 4200-4400 MHz. That section will also then be appropriate for the radar altimeter SARPS once they are completed.

At the World Radiocommunication Conference 2023 changes were agreed to the international radio frequency regulations which provide for sharing of the frequency band 4200-4400 MHz by WAIC systems under the aeronautical mobile (route) service, and radio altimeters under the aeronautical radio navigation service. The associated ITU Resolution 424 (WRC-15) requires that the WAIC systems protect the operation of the radio altimeters and operate in accordance with SARPs as contained in Annex 10. Also, there was a plan to develop and maintain standards and regulation practices (SARPs) and guidance to prevent WAIC/radio altimeter interference.

Looking to the future, WAIC will bring significant advantages in efficiency and flexibility while reducing the costs of installation and maintenance over traditional avionics networks. While progressing steadily, there remain WAIC technical challenges and fundamental design principles that must be fully developed and deployed.