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

FDADS SIMULATION AT DENVER
A demonstration simulation of the Full Digital Automated Radar
Terminal Display System (FDADS) was conducted November 16 and 17,
1992. Thirty-six 30° blunders were simulated, of which 12 were
shown by later analysis to be at-risk. Three TCV's were found
among the 12 at-risk blunders, resulting in an observed TCV rate
of 1/4. After two days of simulation, the decision was made by
FAA management to discontinue the FDADS simulation in favor of
the FMA. The analysis presented here will support that decision.
The analysis will show that the TCV rate for the FDADS simulation
is significantly larger than the TCV rate for the FMA simulation.
The analysis will also show that the larger TCV rate of the FDADS
simulation could lead to an unacceptably large risk.
Although the sample size is small, some conclusions regarding the
data may be drawn. Since the number of at-risk, worst-case
blunders was much larger for the FMA simulation, the observed
Bernoulli ratio for the FMA simulation may be regarded as much
more accurate than that for the FDADS simulation. The observed
ratio for the FMA simulation was 2 TCV's per 186 at-risk
blunders, or 1/93. Since binomial probabilities are easily
computed, the null hypothesis that the probability of a TCV
during the FDADS simulation is the same as that for FMA, Ho:p =
1/93, may be tested against the alternate hypothesis, H1:p >
1/93, directly from the binomial distribution. A significance
level of 0.05 will used to lessen the likelihood of a type I1
error.
If the probability of a TCV during the FDADS simulation was also
p = 1/93, then the probability P of observing 3 TCV's in a sample
of 12 at-risk blunders would be given by:
r2)(lI(gr
= 0.000248.
P = 3 93
The probability of 3 or more TCVIs in a sample of 12 may also be
computed and is found to be P = 0.000254. Since the probability
of 3 or more TCV's in a sample of 12 is smaller than 0.05, the
alternate hypothesis, that the probability of a TCV using FDADS
is larger than the probability of a TCV using FMA, is accepted as
being true.
If the upper confidence limit for the FMA simulation, 5 TCV's per
102 at-risk blunders, is used for the estimate of the probability
of a TCV given an at-risk blunder, then the null hypothesis would
be Ho:p = 5/102 and the alternate hypothesis would be H1:p >
5/102. The probability of 3 TCVIs in a sample of 12 at-risk
blunders, assuming p = 5/102 is computed as follows: