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Comments or questions concerning information contained within may be directed to the ASRS at
P.O. Box 189, Moffett Field, CA 94035. That does it for this issue of ASRS Directline
Charles Drew, ASRS Directline Editor
4 June 1993
4 Issue Number 4
The upsurge in TCAS incident reporting
to the ASRS points to a growing controversy
between flight crews and air traffic controllers.
While flight crews appear to whole-heartedly
endorse its use, others, specifically air traffic
controllers, feel that the difficulties and teething
problems of this new technology may mean that
the genie is out of the bottle — and out of control.
Background for TCAS II
Since 1955, the aviation community has strug-gled to conceive and
implement an automated airborne collision avoidance system as a
backup to the air traffic control system. In 1981, Administrator J.
Lynn Helms committed the resources of the Federal Aviation
Administration (FAA) to the development of an airborne system by
1985. Based on 1987 congressional legislation, the FAA mandated
the installation of Traffic Alert and Collision Avoidance System
(TCAS II) equipment on all airliners by the end of 1993. To date,
approximately 70 percent of the air carrier fleet and over 400
business aircraft are TCAS II equipped. Two thousand TCAS II
aircraft have flown over 2.5 million revenue miles protected by a
technology that is generating discussion and even controversy
among pilots and controllers .
ASRS Takes a Look
On July 29, 1992, at the request of the FAA’s Office of Aviation Safety
and the National Transportation Safety Board (NTSB), the ASRS
provided an analysis of TCAS II incident reports. A random sampling
of 170 TCAS II incident reports were coded and analyzed by a
team of ASRS pilot and controller analysts in a Quick Response (QR)
effort. An ASRS QR is an intensive, time-limited analysis of ASRS
incident data. Although lacking some of the features of a more
traditional research effort, QRs are capable of providing a useful and
quantifiable “snapshot” of topical issues. This analysis made the
overall assessment that TCAS II has definitely enhanced safety, but
still has a number of technical and human-machine interface
problems.
Note: As all TCAS units in current use are TCAS II systems, TCAS
and TCAS II are used synonymously in this review.
TCAS II Saves
There are many incident reports where flight
crews assert that TCAS “saved the day.” An air
carrier captain writes:
“On base leg…we were cleared by Center for [the]
visual…Immediately after accepting the visual,
Center reported pop-up traffic at 11-12 o’clock,
level. I noticed an RA on the TCAS II with visual
commands to pull up. After climbing 200 to 300
feet, I noticed a [light aircraft]…cross under us
about 200 feet below. The alert Controller at
Jacksonville Center, reinforced by the [TCAS II]
RA command, …prevented a possible mid-air.
TCAS works.” (ACN 213749)
And in another air carrier report…
“Hazy holiday weekend in Southern California
(LA basin). Many, many VFR aircraft in [the]
area. My crew alert for traffic. TCAS scope
cluttered with traffic. On departure…climbing…
[a] traffic conflict [at] 12:30, 3 miles, 500 to 1,000
feet above [was noted] on TCAS. I hoped to climb
(zoom) above it as soon as it was acquired
visually. However, it was not acquired visually
until after evasive action was taken based on
TCAS II RA and ATC traffic advisory. TCAS
and ATC saved the day.” (ACN 179784)
This is the good news about TCAS, but these
benefits have not been gained without some sideeffects.
by Vincent J. Mellone
Issue Number 4 5
TCAS II: Issues and Incidents
Most TCAS II issues reported to the ASRS encompass anomalous or
erroneous operation of TCAS II equipment, TCAS-induced distraction,
airborne conflicts provoked by TCAS, and non-standard use of
TCAS.
TCAS II Equipment Issues
Early versions of TCAS II equipment displayed some hardware and
software anomalies. The reliability of TCAS equipment has improved
considerably, but there continue to be some problems — as
this recent report illustrates. An air carrier flight crew departed an
airport at night in mixed meteorological conditions. With high
terrain very near, they experienced a very frightening situation:
“Climbing through 1,200 feet [on departure] we had a TCAS II
Resolution Advisory (RA) and a command to descend at maximum
rate (1,500 to 2,000 feet per minute). [The flight crew followed the
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