AMCP WG3WP5 OPERATIONAL COMMUNICATION REQUIREMENTS HISTORICAL THE

AMCP WG3WP5 OPERATIONAL COMMUNICATION REQUIREMENTS HISTORICAL THE






Report to AMCP/8: Operational Communication Requirements

AMCP WG3/WP5

Operational Communication Requirements

Historical

The development of radio communication and powered flight are closely related. Guglielmo Marconi made his first radio transmission across the Atlantic just two years before the Wright Brothers made their first successful powered flight. The first known use of air/ground radio communication was during World War I, when some military pilots took radios aloft with them to allow them to report on their observations. During these early days of spark-gap transmitters, the only means of radio communication was radiotelegraphy, requiring a dedicated communications officer (or a very busy and talented pilot) in the cockpit and an operator on the ground. By the early 1930's, radiotelephone apparatus became reliable enough for air-to-ground use and was also much lighter than earlier equipment.

Before 1940, practically all communication was within the LF and HF bands. Airplanes transmitted in the HF band and ground stations answered in the LF band. For longer-distance communication, ground stations also transmitted in the HF band. At that time the standard answering frequency for towers was 278 kHz and, because the low-powered ground wave could be heard only in the vicinity of the airport, there was little interference. ARINC began providing en-route flight following and weather information in the domestic United States via HF in 1934. Of course, HF voice has continued until very recently to be the only viable option for flight over oceans and other sparsely populated areas where there are no line-of-sight ground stations.

Research during the 1930's indicated that the VHF band offered a better means of air-ground and air-to-air communication and the decision was made to utilize the band of VHF frequencies now in use. In 1934, the United States FCC opened the VHF spectrum and assigned to ARINC the aeronautical mobile navigation and communication frequencies from 108 through 136 MHz. Most of those frequencies have since been passed to the FAA. The rest of those frequencies continue to be administered by ARINC for aeronautical operational communications. The first VHF radio trials were conducted in the summer of 1938 and production VHF radios were delivered in the fall of 1941 for commercial airline use.

[This description is very US-centric. A contribution concerning radio history in Europe and elsewhere in the world to balance this view would be most welcome.]

Broadcast radio has been used for aviation weather and airport information (ATIS), using either a VHF communication channel or the voice portion of a VOR signal. Communication of digital messages in commercial service between the aircraft and the ground was begun in 1977, when ACARS messages were first transmitted.

Modern air/ground civil communications includes not only HF and VHF radio links but also satellite communication of voice and data, HF data links, and various experimental or prototype systems of communication. In addition, the passenger has been afforded telephone (both voice and data) communications with the ground via satellite, dedicated UHF technologies and cellular services.

Quality of Service

Quality of service for any air/ground communication link may be expressed in three terms — delay, integrity, and availability. A minimum quality of service needs to be specified for each type of service and operational scenario.

Since quality of service is often strongly correlated with cost of service, over-specifying quality of service for a specific type of function and operational scenario will cause increased costs and may prevent the service from being implemented.

Although the terms of reference for ICAO relate only to services to support operational safety and regularity, a consistent set of requirements for all air/ground communications, including passenger and administrative services, is useful to enable integrated solutions where possible. Passenger and administrative services also have quality of service requirements. Instead of being based on a safety analysis, passenger and administrative quality of service are justified by user satisfaction and efficient operation. A passenger or crew telephone connection would require minimal delay and moderate integrity (providing a voice quality nearly equivalent of land-based long distance service); non-availability during portions of the flight or ground operations might be acceptable. A passenger or crew e-mail, on the other hand, could probably accept a relatively large delay and limited availability but would require relatively high integrity.

Users

Users are located both on the aircraft and on the ground. The cockpit crew and air traffic controller are the first, and perhaps the most critical, pair of users normally considered. Other pairs of correspondents might include:

As illustrated in the above list of examples, not all users are people, either in the aircraft or on the ground. Allowing a human to request information from a database might more efficiently provide much of the information that must flow today through human operators. Automatic synchronization of ground and airborne databases (e.g., weather, flight plan, flight schedule, special use airspace, popular web sites) provides a way to use off-peak communication capacity to reduce user-perceived delay during subsequent delay-sensitive operations.

User Information

The true users' requirement is to be able to convey information accurately, quickly, with a minimum amount of workload and other overhead function. Whether that information is a simple "Wilco" response to an ATC clearance, a complex graphic weather product to be processed by a flight crew member or a flight management computer, or a synoptic data dump from an onboard maintenance computer to an airline analysis computer, the communication link should provide a quality of service appropriate for the requirements of the function without imposing undue constraints or distortions. The communication link should be able to handle not only functions used during current operations but also new functions developed for operations of the future.

Users share information in a number of ways. Two-way analog voice is the traditional, and most widely used, information sharing method. Broadcast voice is used for some weather products and for ATIS. Digital two-way data link has been used for aircraft operational data delivery (for both airline and corporate operations) and has recently been used for some air traffic services. Broadcast data transmission is being tested for ADS, for traffic information, and for weather.

Some of these information-sharing methods are marginally effective but, until recently, were the only methods available. A prime example is the use of repetitive audio broadcast for ATIS. A human operator must read weather and related information from a screen or printout, generate a script for an hourly ATIS message, read that message into a recorder, and enable the recording to be broadcast continually on a VHF Comm. or VOR voice channel. A flight crewmember must tune a receiver once within radio range of a ground transmitter, listen to the broadcast, and transcribe the information into written form where it may be referenced by all of the crewmembers. This process is workload-intensive at both ends, continually uses a valuable radio channel for information that typically changes only once an hour, has a high probability of transcription errors at both ends, and provides a cumbersome method of ensuring that last-minute information is provided.

A key concern when transitioning from operations using two-way voice to operations using addressed messages, either voice or data, is the loss of the "party line". Pilots gain a certain amount of situational awareness by listening to transmissions to and from other aircraft. For instance, a pilot listening to the dialog with aircraft ahead of him on the Approach Control frequency can anticipate future speed changes, altitude clearances, etc. Also, comments about windshear, turbulence, icing, and other weather phenomena can be instantly shared among all aircraft sharing a frequency, with no additional workload by any of the participants. The negative aspects of "party line" include the fact that a pilot may anticipate a clearance and fail to notice that his clearance is not the same as that given to the previous aircraft. Another problem with "party line" is the workload involved in listening to the radio traffic and filtering the important from the unimportant. Part of this workload includes accurately hearing transmissions intended for the subject aircraft and the hazards involved with either inadvertently responding to a clearance meant for another or failing to respond to a clearance meant for the subject aircraft.

Capacity

Calculating the required capacity for future air/ground communications is a complex operation. The calculation must consider, inter alia,

The number of aircraft and their distribution are assumed to be beyond the control of air traffic or communications experts. The demand of additional flights and the density of those flights will continue to place additional demands on air traffic control. The operational concept for air traffic control provides the biggest leverage for improved operations. Improved efficiency of operations and of communications can allow existing radio channels to be used in a more efficient manner, allowing more aircraft to communicate with existing radio resources. The work of AMCP — to develop additional radio channels and to specify efficient use of those channels — is a necessary activity, but not the only means, for providing the necessary communication for air traffic safety and efficiency.

Technologies

The operational requirements for aeronautical communications should not specify technologies but should specify capacity and quality of service using technology-independent terminology. Due to imperfect technology, no known solution perfectly meets all requirements. Therefore, engineering judgment must be applied to judge technologies and weigh the various requirements to iteratively approach the technologies that most nearly meet all of the requirements.









Tags: communication requirements, necessary communication, operational, historical, requirements, wg3wp5, communication