Published Report (DOT/FAA/CT-94-36)

4.7 TECHNICAL OBSERVER STATEMENT.
The technical observers unanimously agreed that controllers
appeared to separate aircraft with relative ease. In their
report, the technical observers stated that during the
simulation, the controllers had little difficulty detecting and
resolving blunders. In some cases, controller response times
were actually slower, as the controllers took time to evaluate
the situation prior to issuing instructions to the evading
aircraft. Alert algorithms and runway spacings appeared to be
factors which allowed controllers to take extra time when
evaluating certain situations.
In conclusion, the technical observers unanimously agreed,
ll...triple simultaneous approaches at the DIA airport can be
safely accomplished using the 4.8 second update radar and the
final monitor aid.
4.8 RISK ASSESSMENT.
The analyses above have assessed the controllers' ability to
resolve blunders during simultaneous parallel ILS approaches. It
was observed that the controllers were not always able to
maintain the test criterion miss distance of more than 500 ft
between the blundering aircraft and aircraft on adjacent
approaches. To properly evaluate the proposed operations, the
effect of implementing the proposed operation on the level of
risk found in today's operational environment must be determined.
Ideally, the probability of an accident during the approach
operation could be computed and compared to an acceptable
probability. However, since the majority of approach operations
are conducted to single approaches, no recorded accident has ever
been attributable to a blunder occurring during multiple approach
operations. Accordingly, little effort has been made to record
and track blunder occurrences.
A way to complete the risk analysis without operational blunder
data is to determine a target risk value, and then to compute a
blunder rate which would result in the target risk value. This
would provide insight to the safety level of the operation, and
allow the FAA to assess the acceptability of the operation. The
computed blunder rate should not be used as the sole determining
factor of whether the operation meets the target risk value.
The total number of air carrier accidents as well as the number
of fatal accidents on final approach has been extracted from the
National Transportation Safety Board (NTSB) data for the time
period, 1983-1989. This number, together with the total number
of ILS approaches during the time period, lead to an estimated
fatal accident rate during ILS operations performed during IMC of
4 x fatal accidents (ACC) per approach (APP). There are a
40