Chapter 20
Traffic Alert and Collision
Avoidance System
TCAS
http://www.youtube.com/watch?v=x7IJyP4h2EE
TCAS
The heart of the TCAS system is the transponder.
Aircraft with Mode C transponders will respond to interrogations with altitude
information.
Aircraft with Mode S transponders will respond to interrogations with address
information.
If another aircraft is within range, it will respond to the interrogation, the first
aircraft will measure the time difference to compute the range of the other
aircraft.
Because TCAS operates aircraft-to-aircraft, it is not dependent on ground
stations.
The TCAS system issues 2 types of alerts: a TA which is a threat advisory that
alerts the pilot that another aircraft is close enough to be a potential threat; a
RA is a resolution advisory that means the other aircraft IS a threat (30
seconds to a possible collision) and issues commands to evade a collision.
TCAS on a Radar Display
Textbook page 148
TCAS on Vertical Speed
Indicator
TCAS on Vertical Speed Indicator
The red arc indicates the area to avoid, the pilot always
shoots for the green arc.
In this example, the airplane is descending at about 3000
feet per minute.
Textbook page 149
TCAS on an EFIS screen
Textbook page 149
TCAS Warnings
Textbook page 152
TCAS System Block Diagram
Textbook page 150
TCAS System Components
Textbook page 151
TCAS I was developed to accommodate the general
aviation (GA) community and the regional airlines. This
system issues ‘Traffic Advisories’(TAs) to assist pilots in
visual acquisition of intruder aircraft. TCAS I is mandated
on aircraft with 10 to 30 seats, although TCAS II may be
installed instead.
TCAS II Provides the information of TCAS I, and also
analyzes the projected flight path of approaching aircraft
and issues ‘Resolution Advisories’ (RAs) to the pilot to
resolve potential mid-air collisions. TCAS II is required
internationally in aircraft with more than 30 seats or
weighing more than 15,000 kg.
Nov 1, 2004 – May 31, 2005
Ueberlingen July 2002
ADS-B
Automatic Dependant SurvailanceBroadcast
http://www.faa.gov/nextgen/implementation/programs/adsb/
Sec. 91.113 — Right-of-way rules:
Except water operations.
(b) General. When weather conditions permit,
regardless of whether an operation is conducted under
instrument flight rules or visual flight rules, vigilance
shall be maintained by each person operating an
aircraft so as to see and avoid other aircraft. When a
rule of this section gives another aircraft the right-ofway, the pilot shall give way to that aircraft and may not
pass over, under, or ahead of it unless well clear.
Review Q & A Chapter 20 TCAS
20.1 A TCAS aircraft transmits an interrogation once per ____.
Answer: second.
20.2 How does an intruder aircraft with an ATCRBS (early type) transponder reply to TCAS
interrogation?
Answer: Only a TA
20.3 How does an intruder aircraft with a Mode S transponder reply to TCAS interrogations?
Answer: Both a TA and RA
20.4 How does TCAS determine the direction of a threat?
Answer: From its directional antenna
20.5 How does TCAS determine the distance of a threat?
Answer: By using Tau and using the range rate.
20.6 How does TCAS determine whether the other aircraft is a threat?
Answer: By using range rate
20.7 What is the concept of “Tau”?
Answer: Compensation for varied speeds and performance
20.8 Name the 2 kinds of warnings issued by TCAS.
Answer: TA (Threat Advisory) and RA (Resolution Advisory).
20.9 Does a Threat Advisory (TA) command the pilot to maneuver out of the way?
Answer: No.
20.10 What does a Resolution Advisory (RA) do?
Answer: Issues evasive maneuvers
20.11 If 2 TCAS aircraft are closing, what prevents them from climbing, and flying into each other?
Answer: Coordinated Resolution Advisories
20.12 What is the technique of “whisper-shout”?
Answer: Buffering of replies to prevent alert overload
20.13 How does the directional antenna reduce the number of replies for each interrogation?
Answer: By only responding to interrogations in the active quadrant.
Conectors
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