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Independent Variables
CAT Detection Sensor
CAT sensors of three different ranges are modeled in the experiments and compared to a nominal no-sensor case. Only one sensor range is modeled in a given traffic scenario, and all aircraft in that scenario are equipped with the same sensor range.
Ranges of four, sixteen, and 40 nautical miles are modeled in the experiments. Table III-5 presents the details and rationale for the selected CAT sensor ranges. A four-nautical-mile range was selected as it corresponds to the range evaluated by NASA Glenn Research Center in convective turbulence remote sensing efforts. Based on the results of the focused interview, it was found that aircraft response to CAT would significantly differ based on “look-ahead times” (or warning time associated with a forward looking remote sensor) of about two and five minutes: a two-minute look-ahead time would provide sufficient warning for a flight crew to turn the seat-belt sign on and for most passengers to react to it by fastening their seat-belt prior to entering the turbulence zone; a five-minute look-ahead time would provide sufficient warning for a flight crew to request a vertical deviation and initiate a vertical re-routing maneuver prior to reaching the turbulence zone. For aircraft cruising at 480 knots (equal to the mean plus one standard deviation of the aircraft speed distribution), such look-ahead times would correspond to CAT sensor ranges of sixteen and 40 nautical miles, respectively.
Also based on the results of the interview, it was decided to model the CAT sensor with a turbulence detection threshold corresponding to moderate or greater turbulence. The information provided by the sensor would either be information that there is “no moderate turbulence detected” or that there is “moderate or greater turbulence” ahead of the aircraft, somewhere within the range of the sensor.
Table III-5 Details and Rationale for CAT Sensor Range Evaluated
CAT Sensor Range (nm)
Equivalent “Look-Ahead Time” at 480 kts
Rationale
4
30 sec.
Range corresponds to convective turbulence sensors investigated in NASA GRC’s study
16
2 min.
“Look-ahead time” provides sufficient warning for most passengers to fasten their seat-belt
40
5 min.
“Look-ahead time” provides sufficient warning for vertical avoidance of turbulence
The technology investigated for the remote detection of CAT includes LIDAR, which relies on the presence of aerosols. It is likely that issues such as the scarcity of aerosols at high altitudes would limit the performance of LIDAR to detect clear air turbulence. For simplicity in the initial experiments, the CAT sensor accuracy is not varied and the influence of sensor limitations is not investigated in these experiments, but could be investigated at a later time.
CAT Level Along Planned Aircraft Paths
Various scenarios of CAT encounter are modeled along the various aircraft routes, corresponding to:
Light CAT only
Light and moderate CAT
Light, moderate, and severe CAT
The details of variations of CAT along planned aircraft routes are found in Table III-3.
Performance Measures
Performance measures were planned in the experimental design in relation to the exposure of aircraft to CAT, to the response of flight crews and controllers to the CAT events and sensor warnings, and to the amount of resulting controller-pilot communications, as described below.
Aircraft Exposure to CAT
In order to assess the exposure of aircraft equipped with the three CAT sensors, statistics (mean and standard deviation) for each of the following were specified:
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