2. 1. From 1 July 2003, all turbine-engine
commercial air transport aeroplanes of a
maximum certificated mass in excess of 15000 kg
or with a maximum approved passenger seating
configuration in excess of thirty (30) passengers,
shall be fitted and operated with serviceable
equipment meeting ACAS II specifications.
(121.05.15)2. From 1 January 2005, all turbine-engine
commercial air transport aeroplanes of a
maximum certificated mass in excess of 5 700 kg
or with a maximum approved passenger seating
configuration in excess of nineteen (19)
passengers, shall be fitted and operated with
serviceable equipment meeting ACAS II
3. SCOPE
1. Introduction.
2. ACAS II Principles.
3. Cockpit Presentation.
4. Aural Annunciations.
5. Use of ACAS indications.
7. Controls and Displays.
8. Collision Avoidance Logic.
9. Additional changes.
6. Standard Phraseology.
EXAMINATION
1. Multiple answer format.
2. 90% passmark.
4. INTRODUCTION
ACAS II is a system used for detecting and tracking
aircraft in the vicinity of your own aircraft.
It interrogates their transponders, analyzing the replies
to determine range, bearing, and if reporting altitude, the
relative altitude of the intruder.
Should a possible collision hazard exist, it issues visual
and audio advisories to the crew for appropriate vertical
avoidance maneuvers.
ACAS is unable to detect any intruding aircraft without
an operating ATC transponder (operating in Mode A and
C) or a Mode S transponder.
5. ACAS II issues two types of advisories:
Traffic Advisory (TA). Showing the intruding
aircraft's relative position and altitude with a
trend arrow to indicate if it is climbing or
descending. The display is usually a dedicated
instrument.
Resolution Advisory (RA). Showing the
required vertical speed to avoid an airborne
collision. The display is incorporated in the VSI.
INTRODUCTION
ATC procedures will continue to be the primary
means of ensuring aircraft separation.
6. ACAS logic based on two main concepts:
1. The warning time, which is based on the time-
to-go to the Closest Point of Approach (CPA)
2. The sensitivity level, which is a function of the
7. When RA triggered:
1. Computes most appropriate vertical
manoeuvre to achieve target vertical miss
distance (600 ft).2. Tries to prevent vertical crossing RA’s.
3. Advisory strength continuously evaluated
and modified if necessary.
Multiple threat encounter:
1. Attempts to resolve in single RA.
2. Otherwise with a composite RA of non-
contradictory climb and descend.
8. COCKPIT PRESENTATION
The cockpit presentation provides limited
information on adjacent traffic, TA’s and RA’s, and
aural annunciations.
The traffic information display system is designed to
aid visual acquisition of an intruder.
ACAS display
center
2 NM range
circle
Display
range
9. RA -Vertical rate to
be avoided
RA - Required
vertical rate
COCKPIT PRESENTATION
13. ADDITIONAL CHANGES
ACAS II Bulletin No 5 – October 2004
“Pilots shall respond immediately by following the RA
as indicated, unless doing so would jeopardise the
safety of the aeroplane”
“Pilots shall follow the RA even if there is a conflict
between the RA and an ATC instruction to manoeuvre”
“Visually acquired traffic may not be the same traffic
causing an RA. Visual perception of an encounter may
be misleading, particularly at night.”
“Pilots shall not manoeuvre in the opposite sense of
an RA”
14. SUMMARY
ACAS is a “last resort” tool designed to
prevent mid-air collisions.
ATC procedures to provide flight safety must
continue.
