niques for use in cooperative systems were then evaluated. Threat logic had to be developed. At one point success seemed so near that airlines actually placed orders for equipment, but problems arose which forced the manufacturer to cancel the orders. One of the consistent concerns was that the equipment required to prevent collisions with general aviation planes would be too complex and too costly for widespread use by general aviation planes. Thus the proposal to utilize the radar beacon equipment already installed in many general aviation planes had great appeal. That proposal which has evolved into what is now known as the beacon collision avoidance system, BCAS, is not the mainstream of the FAA's CAS developmental effort. Simultaneously, the FAA is developing the discrete address beacon system, DABS, and the automatic traffic advisory and resolution service, ATARS. The FAA is also investigating the possibility of what they call full BCAS. Incidentally, I would insert here that you asked earlier the cost of a BCAS, and somewhere at variance with the answer given, the answer I've been given is the cost of a single, active-only BCAS-that's the first effort that the FAA is addressingthat a single unit would cost in the neighborhood of $20,000. Therefore, in a dual installation in airline aircraft that would be $40,000 for the equipment. Then, if you add the installation cost and spares, it's estimated to be around $50,000. Again I emphasize, for the active BCAS only. We have no information whatsoever as to what a socalled full BCAS that the FAA talks about would cost. It's too far, it's too embryonic at this stage to put a cost on it.

We believe that the FAA is correct in moving toward active BCAS, DABS, and ATARS. Much more needs to be known about full BCAS before we can comment on its possible utility. The whole CAS effort has moved much more slowly than any of us would have liked. Some apparently feel that it has been inordinately delayed. We believe the FAA has been unfairly criticized in view of the highly complex nature of the problem.

Looking to the future, we would urge the FAA to acquire the factual information necessary to insure sound decisions on BCAS, DABS, and ATARS as quickly as is technically possible. Then, but not before then, decisions on how to proceed should be made and implemented. The airlines pledge their continued participation and support for such an expedited effort.

In summary:

First, nothing can ever displace safety as the No. 1 consideration in aviation. With regard to collision avoidance, the airlines will continue to devote their energy and resources to achieving their objective of zero collisions.

Second, the FAA's CAS effort should be expedited so that prompt, but not premature, conclusions can be reached and implemented. Third, we believe in a cooperative approach to problems related to airport capacity.

Fourth, additional airport facilities to accommodate airlines and general aviation should be provided. Congressional help may be needed.

This concludes my statement, Mr. Chairman. [The attachments referred to follow:]

RADIO TECHNICAL COMMISSION FOR AERONAUTICS, 1978 ANNUAL ASSEMBLY MEETING WHERE DOES AIRCRAFT SEPARATION ASSURANCE (OR CAS) Now STAND? AN HISTORICAL PERSPECTIVE AND PROJECTION

(By Frank C. White, Director, Information Systems and Avionics, Air Transport Association of America)

Beginning in 1955, over twenty years ago, the airline industry, working through ATA, began its search for an airborne Collision Avoidance System (herein called CAS). It was done with full recognition that doing so might create concern in the minds of those who depended on the airlines for transportation. A joint meeting of RTCA and the Institute of Radio Engineers was selected as the forum for laying out the problem and the need for a solution.1 Nothing much happened until about eight months later when two airline aircraft collided over the Grand Canyon. This incident generated renewed interest and numerous "solutions" were offered. In July 1956 ATA sponsored a symposium in Washington, bringing together experts, engineers and inventors, to compare airline requirements against the then current state-of-the-art.

As a result of the symposium, Collins Radio in September 1956, submitted the first formal proposal to the airlines. It was for a non-cooperative Pilot Warning Indicator (PWI) System which they believed could later be developed into a Collision Avoidance System (CAS).2 Two million dollars worth of airline orders were placed with Collins within 60 days. In the development work that followed, Collins Radio discovered that normal aircraft accelerations in flight would prevent their airborne doppler radar from making reliable collision predictions, or could create erroneous predictions in a significant percentage of cases. This eliminated the CAS feature of the Collins proposal. Collins withdrew its proposal and resumed its analytical work, which continues to this day.

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3

Often after something is invented, everyone observes that the obvious was invented; such was the case when Dr. Morrel invented what he termed Tau. Tau is the measurement of range to the intruding aircraft divided by the range rate which gives time to collision assuming that the altitude of both aircraft is known. The invention of the Tau concept by Dr. J. Smilie Morrel of Bendix Radio in the mid-1950's and his paper which provided the first accurate description of the fundamental physics of the airborne collision avoidance problem 5 even today remain two basic references for filtering out poor ideas/solutions that do not address the problem to be solved.

Footnotes at end of attachment 2.

In 1960 a collision between two fighter aircraft being tested by their manufacturer, McDonnell Aircraft Corporation, sparked an all-out effort by McDonnell to develop a CAS for use in their flight test area. This was the birth of the CAS now identified as "Time Frequency" System. By the time is development was completed in the mid-1960's, the McDonnell Douglas Time-Frequency CAS met and solved most of the nagging problems of an airborne CAS. It used one-way ranging (requires extremely accurate time source), direct doppler measurement of range rate, a unique "time slot" for each aircraft to make its transmission, an exceptionally simple and readily identified pulse format for communicating aircraft altitude, bi-phase modulation of the carrier providing ample communication capability, and many other features that were quite advanced for its time.

By 1962 FAA became active in CAS System development and formed its Collision Prevention Advisory Group (COPAG). FAA sponsored a COPAG organized industry-wide symposium on the state of CAS investigations, and received widespread support and interest from all segments of aviation. At the symposium Bendix Radio described a CAS based on the Tau concept, using oneway ranging and employing the ground-bounce technique. Collins Radio outlined a method for testing by computer simulation the features of any proposed CAS. The Collins contribution was important since it offered for the first time a quick, minimum cost method for choosing the most promising techniques from among a wide variety of theoretical concepts. In the Fall of 1963 FAA contracted with Collins to study CAS techniques by simulation and by mid-1965 a (draft) Collins report was available. Collins then stated that the Time-Frequency System was the most promising, that it should work quite well for the enroute situation, but would have some limitations in the terminal area-where aircraft are most likely to be maneuvering in flight.

At an ATA meeting in mid-1965 Collins reported on its studies and McDonnell showed the Time-Frequency CAS equipment it was prepared to use in their flight test operations beginning later that year. Operations Executives of the airlines were sufficiently impressed by the McDonnell system to encourage its continued development, and resolved that the interaction between the TimeFrequency CAS and the Air Traffic Control System should be carefully analyzed since this seemed to be an area where the system appeared most vulnerable. At that point a CAS Technical Working Group was formed by the ATA to expedite CAS System development and to prepare a technical description of the system that would meet airline requirements. By late 1967 ATA Report, ANTC No. 117, was issued."

At that time, ATA asked FAA to use the CAS System description (specifically ANTC 117):

(a) To test by real time operational simulation the interaction of CAS and ATC to determine if operation of the CAS would adversely affect air traffic control.

(b) As a starting point for developing a National Standard for airborne Collision Avoidance Systems, including both civil and military aircraft.

(c) To begin efforts that would be needed to secure international standardization on a single, internationally accepted system for airborne CAS.

On December 14, 1967, as a result of progress made by the ATA CAS Technical Working Group, the Board of Directors of ATA approved a cost plus fixed fee contract with Martin-Marietta Company to evaluate prototype airborne CAS Systems to meet the ANTC 117 requirement. $1.85 million of airline money and about an equal amount of manufacturers money was expended to provide for flight evaluation of Time-Frequency CAS hardware built by Bendix Avionics, McDonnell Douglas and a Sierra Research-Wilcox Electric team. During the Fall of 1969 the ATA sponsored and funded CAS flight test program accumulated 317.2 hours of flight during the Martin-Marietta flight test program. The final report to ATA concluded as follows:

(a) Time-Frequency CAS was effective in:

(i) Detecting the presence of an intruder.

(ii) Evaluating the collision hazard.

(iii) Selecting the appropriate mutually cooperative evasive maneuvers that achieve safe vertical separation before reaching the potential collision point. (b) Satisfactory CAS performance was achieved by all manufacturers' equipment; intermixing did not influence accuracy.

(c) The Time-Frequency CAS technique was effective in implementing aircraftaircraft interchange of accurate range, range rate and altitude data.

(d) The combined system tolerances displayed the CAS climb/dive commands within five seconds of the desired value 90 percent of the time and within ten seconds 100 percent of the time.

Footnotes at end of attachment 2.

(e) Signal multipath and externally generated interference did not prevent the satisfactory accomplishment of CAS data interchange in all the test conditions. The ATA Board of Directors, in June 1970, noted with satisfaction the successful completion of the airline CAS flight test program and approved an ATA program which had as its objective, "obtaining FAA support for selecting Time Reference CAS as the U.S. National Standard and achieve its early implementation."

By July 1970 an Aeronautical Radio AEEC Characteristic, ARINC 587, for Time-Frequency CAS was approved and published. By June 1971, McDonnell Douglas began flight evaluation of its pre-production ARINC 587 airline CAS equipment, and airlines began making plans (in some airlines complete plans) for ARINC 587 airborne CAS provisions. On June 22, 1971, Piedmont Airlines and McDonnell Douglas Corporation announced that Piedmont Airlines had ordered the ARINC 587 CAS equipment to protect its fleet against midair collisions.89 On July 12, 1971, Senate Bill S-2264 was introduced by Mr. Moss: "To amend section 601 of the Federal Aviation Act of 1958 to require the installation of Collision Avoidance and Pilot Warning Indicator Systems on certain aircraft and for other purposes."

On September 30, 1971 and again on October 12, 1971, the ATA forwarded to the FAA the ATA (Board of Directors) approved airline-recommended program for orderly introduction of CAS into routine flight operations. The key action items requested of FAA were to issue a Draft Advisory Circular stating affirmative views on the following important issues:

1. Endorse the Time-Frequency CAS as the best choice for all U.S. air-space users, and state the intent to work toward the development of a U.S. National Standard for both domestic and subsequent international application through ICAO, beginning with the 7th ANC.

2. Expedite and publish FAA NAFEC real time simulation effort and indicate if CAS could be used in the ATC environment and any expected limitations on its use (beyond those specified by ANTC 117).

3. State minimum operational requirements for CAS equipment in the ATC environment, particularly any changes to those specified by ANTC 117.

4. State the assumptions used by FAA as to method employed to initiate and propogate CAS master time.

5. State FAA intent with regard to an advance Notice of Proposed Rule Making which would require all users of certain airspace to be CAS-equipped by (approximately) 1978.

6. Advise the airlines of the procedure to be followed to obtain approval for operational use of CAS.

If I stopped at this point in recounting the history of airborne CAS development, you might expect that by now, seven years later, Time-Frequency CAS would be implemented in all airline aircraft and widely implemented in many other aircraft. We all know that this is far from what has happened. Without trying to point the finger at any organization or agency, I introduced my discussion of what happened in late 1969 and the early 1970's in airborne CAS by saying that "all hell broke loose." Several manufacturers, who by then recognized that CAS was going to be a potentially b-i-g market, turned their inventors loose and began to deluge the Congress, FAA and DOD with "better" airborne CAS Systems.

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Two proposals for airborne CAS Systems that surfaced at that time were selected by FAA for further development. They were the RCA SECANT (System for the Separation and Control of Aircraft Using Nonsynchronous Techniques) invented by RCA's Jack Breckman, and the Minneapolis Honeywell AVOIDS (Avionic Observation of Intruder Danger Systems). Two Breckman/RCA papers and 11 were particularly devasting since Mr. Breckman claimed the TimeFrequency Collision Avoidance System "will not work—it will not prevent mid-air collisions, but will cause them." ATA testified before the Senate Commerce Subcommittee on Aviation in June 1971 on behalf of the Time-Frequency System, and in June 1971 petitioned the FCC (RM-1801) to allow regular licensing of Time-Frequency airborne CAS.

In early August 1971, the House Committee on Government Operations, Government Activities Subcommittee, held a hearing on Aircraft Collision Avoidance Systems. ATA, Bendix, McDonnell-Douglas and Wilcox Electric all testified that the Time-Frequency System had been fully developed, flight tested and was ready to be implemented providing the government would declare it the selected U.S. system. Minneapolis-Honeywell (Mr. Ronald E. Ericson) testified jointly with Mr. Follen and stated that, "FAA should look at other systems than Time-Frequency." RCA testified on behalf of its SECANT system proposal. FAA