Essay, Research Paper: Collision Aviodance

Collision Avoidance: ADS-B or TCAS
March 7, 2000


INTRODUCTION
Background
Collision avoidance is something that has been a problem in aviation for a long time. Most of the flights conducted today rely on the see and avoid concept and ground radar. Both of which have their flaws. The FAA predicts that mid-air collisions will increase by 300% over the next 20 years due to the increase in flights being flown by all areas of the aviation community (Kraus xiv). Civil aircraft have had onboard protection from midair collisions only since 1990 and general aviation aircraft are not required to have any collision avoidance technology onboard(www.cassd.org 1).
In order to effectively manage the national airspace system in the future we will need to implement Free Flight. Free Flight is a concept designed to enhance safety and efficiency of the airspace by allowing aircraft to choose their own route instead of using victor airways (www.ads-b.com 1). Along with this freedom there is still the problem of aircraft separation which when on an instrument flight plan is air traffic control's (ATC) responsibility. In free flight there may be areas where ATC cannot give the required collision avoidance necessary. In order to safely manage the safety zone around an aircraft, pilots will need to rely on systems installed in the aircraft for better separation.
Purpose
The purpose of this report is to identify whether Automatic Dependence Surveillance Broadcast (ADS-B) or Traffic Alert and Collision Avoidance System (TCAS II) should be placed in all aircraft if the FAA decides that there is a need for some collision avoidance technology to be required for all aircraft. TCAS is currently required on all commercial passenger aircraft over 30 seats and ADS-B is currently being tested.
Scope
In this report, I will discuss:
· Automatic Dependant Surveillance Broadcast (ADS-B)
· ADS-B's Advantages and Disadvantages
· Traffic Alert and Collision Avoidance System (TCAS)
· TCAS's Advantages and Disadvantages
· Summarize which system is better for collision avoidance
Body
ADS-B
ADS-B is a collision avoidance tool that allows aircraft to transmit position, speed, heading and identification via a data link to either other aircraft in the air or on the ground and/or controllers on the ground. ADS-B can also be used with equipped vehicles on the surface movement area.
An ADS-B emitter will periodically broadcast the required information obtained from the onboard navigation systems. Other equipped aircraft will be able to receive this information and view it on the Cockpit Display of Traffic Information (CDTI). The CDTI is a display that shows traffic in relation to your heading. It is a multifunctional display that can incorporate weather and navigation information.
Other aircraft that are receiving the broadcast will be able to avoid a collision and maintain separation much easier than the methods used today. This will lead to safer and more efficient aircraft operations.
ADS-B will be able to provide controllers on the ground with valuable information that they might not be able to see on modern secondary radar. If all aircraft were equipped, separation coverage would be granted everywhere not just in certain areas.
ADS-B will also provide accurate position and identification information of aircraft and equipment on the airport surface area. This will enhance the pilot's and controller's job of avoiding aircraft and vehicles on the ground during times of bad weather.
The FAA has conducted Ground-to-Ground, Air-to-Ground, and Air-to-Air tests on ADS-B. So far these tests have been very successful in all areas (www.faa.gov).

Advantages and Disadvantages of ADS-B
ADS-B offers many advantages for air-to air and ground-to-air
surveillance. First it greatly enhances situational awareness while in flight. The ability to see other aircraft on the CDTI is extremely helpful in adverse weather. Another advantage of ADS-B is its ability to let controllers see aircraft movement out of their surveillance coverage. It also offers reduced communication congestion because controllers do not have to advise of aircraft in the vicinity. On the ground, ADS-B provides some of the same benefits as it does in the air such as reduced communications, situational awareness, and it also provides for reduced taxi and takeoff delays (www.faa.gov 2). ADS-B will increase operational capacity and efficiency by providing more accurate information for the terminal areas.
A main disadvantage of the system is that in order for it to work properly, in the air for collision avoidance, all aircraft need to be equipped. Another disadvantage in the system is that there needs to be a system to obtain the aircraft's position from. When compared with TCAS, ADS-B has the disadvantage that very few aircraft are currently equipped with any of the required technology. Many aircraft are already equipped with transponders that TCAS works with.

TCAS II
The Traffic Alert and Collision Avoidance System is a self contained device that interrogates the transponders of nearby aircraft and presents this information on a display in the cockpit(www.caasd.org i1). When the internal computer senses that there might be a collision course, it first displays a traffic advisory and then if needed, a resolution advisory. The resolution advisory gives the crew a recommended maneuver such as a climb or decent.
TCAS II is required for all aircraft operating in the United States with more than 30 passenger seats. TCAS I is required on all aircraft with 10 - 30 seats.
TCAS I is a short range system that can identify traffic within approximately 3 to 5 nautical miles. It consists of a TCAS antenna, a processor, and a cockpit display. TCAS I shows traffic and displays traffic advisories but does not display resolution advisories (Kraus 175).
TCAS II utilizes 2 antennas, one on top and one underneath the aircraft. It is capable of identifying and resolving traffic 14 miles to the front of the aircraft and 7 miles behind the aircraft. The main advantage that TCAS II has over TCAS I is its ability to calculate resolution advisories (Kraus 175).
TCAS uses both auditory and visual information to announce traffic. Traffic advisories are given audibly just as a warning for pilots. They would still need to look down at the display to see where the traffic is located.
Advantages and Disadvantages of TCAS
The main advantage of using TCAS on all aircraft would be that many aircraft already have transponders. The other advantage is that many commercial transports are already equipped with TCAS I or II.
With the requirement for transport aircraft to have TCAS installed we have discovered some disadvantages. One of the main disadvantages is that it issues too many unnecessary alerts causing altitude deviations and causing pilots to execute unnecessary missed approaches. Deviations may cause pilots to enter another controller's airspace causing an increase in controller workload, which reduces system efficiency when it is at its peak. The unnecessary altitude deviations cause for unnecessary communications between pilot and controller (USGAO 1).


Conclusion
In conclusion, I believe that ADS-B and TCAS are both very beneficial in collision avoidance. Both systems allow the pilots to see and avoid other aircraft. If the FAA were to require all aircraft to be equipped with a collision avoidance technology, I think that the best answer would definitely be ADS-B. Not only does it offer the collision avoidance information, it also serves as a traffic separation tool for ATC on the ground and in the air. ADS-B will bring us one step closer to more efficiently managing our airspace through the implementation of free flight. It could allow for reduced traffic separation in the terminal areas and could move the responsibility of separation from the controller to the pilot in areas of little or no radar coverage.

Works Cited
Krause, Shari, Ph. D. Avoiding Mid air Collisions

New York: McGraw-Hill,1995
United States General Accounting Office. Report to Committee on Science,
Space, and Technology, and House of Representatives.
Users Differ in Views of Collision Avoidance System and Cite Problems.
March 1992.
www.Ads-b.com/Content/plan/sect1.htm
ADS-B: The Plan
www.Cassd.org/research/index.html.
Traffic Alert and Collision avoidance System
www.faa.gov/and/and300/datalink/navsur/adsb.htm
Automatic Dependent Surveillance Broadcat (ADS-B)


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