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Other
Total Citations from 1,997 Records
596
559
374
162
127
33
11
6
4
400
2,272
Table 2 — Airspace Categories of
ASRS Database TCAS Incident Records
TA or RA Incidents
Other TCAS Incidents
Total TCAS Reports
1988
1
5
6
1989
3
6
9
1990
7
32
39
1991
646
205
851
1992
851
241
1,092
Table 1 — TCAS Incident Records in ASRS Database
Total
1,507
489
1,997
Issue Number 4 9
Traffic Was NOT
Observed by ATC
6%
Unknown
28%
Based on 170
of 170 Reports
Traffic WAS
Observed
by ATC
66%
Figure 3 — Traffic Observed by ATC
Quick Response Data Set
Now lets look at the 170 randomly selected records
that comprised the QR data set. There were 159
incident reports by pilots, and 11 controller reports.
In 153 of 170 incidents, flight crews received both a
TCAS II TA and RA. For those 153 records, Figure
1 shows what pilot avoidance action was based on.
Note that in the majority of incidents, avoidance
action was based on the RA.
Figure 3 shows whether or not ATC observed the
TCAS II traffic for the entire 170-report QR data
set. In the majority of instances, ATC did “see” the
traffic.
In 111 of 170 incidents, the reporter provided
information about visual acquisition of their TCAS
II targets. Figure 2 shows when and if traffic was
acquired visually by the flight crew. In 68 percent
of incidents, the flight crew never sighted their
traffic.
Pilot Judgment
TCAS II RA Ignored
8%
Unknown
7%
Traffic Advisory
( TCAS II TA )
less than 1%
Resolution Advisory
( TCAS II RA )
Based on 153 84%
of 170 Reports
Figure 1 — TCAS II Action Based On…
TCAS II Display
used to Locate Traffic
Pointed Out by ATC
less than 1%
Traffic Sighted
Before TA — 8%
Traffic Sighted After TA,
but Before RA — 21%
Based on 111
of 170 Reports
Traffic
Never Sighted
68%
Figure 2 — Traffic Sighting by Flight Crew
10 Issue Number 4
TCAS II — Genie Out Of The Bottle?
Figure 4 — Traffic Advisories Issued by ATC
Based on 136
of 170 Reports
No Traffic
Advisory
Given by
ATC
35%
Traffic Advisory Given
After RA — 18%
Traffic Advisory Given
After TA, and
Before RA — 21%
Traffic Advisory
Given Before TA
26%
Figure 4 indicates that ATC provided traffic
advisories in 136 of 170 TCAS II incidents. There
were 34 instances in which ATC response to a
potential conflict was unknown. According to
reporters, ATC did not provide a traffic advisory
in 48 of 136 TCAS II incidents (35 percent).
TCAS II enhanced safety
TCAS II “saved the day”
TCAS II assisted in visual sighting of intruder aircraft
TCAS II prevented an NMAC (near mid-air collision)
TCAS II derogated safety
TCAS II increased workload
TCAS II prevented an airborne conflict/less severe
TCAS II caused a loss of standard separation
TCAS II display is too cluttered or distracting
Total Citations from 170 “QR” Reports
94
55
52
47
27
7
7
6
6
301
Table 4 — TCAS II “Quick Response” Key Findings
Table 4 shows how reporters felt about TCAS II.
Reporters could express more than a single
opinion; thus there are 301 individual responses
(citations) from 170 reports. In 94 instances, the
reporter stated or implied that TCAS enhanced
safety. This table provides the key findings of the
Quick Response analysis effort, indicating that
reporters in the 170-record QR data set strongly
endorse the safety value of TCAS II. However, this
finding is undoubtedly influenced by the relatively
large percentage of these reports that come from
pilots rather than controllers.
Issue Number 4 11
Recommendations
The ASRS analyst staff are certainly no wiser than
those in government and industry who are
grappling with TCAS II issues, nor would we
make suggestions that conflict with TCAS II
standard operating procedures. Nonetheless,
review of TCAS II incident reports does suggest
that there may be ways to deal with, or even avoid
a TCAS incident.
Controllers
■ High rates of climb and descent, particularly in
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