Home' RTCA Documents for Review : DO-220A Change 1 Contents Appendix B
DO-220A Change 1
© 2018 RTCA, Inc.
1. True Airspeed:
F-factors will differ in the data sets developed for airspeeds of 120, 150, and 200 KTAS. Since the
calculation of F-factor is weakly dependent on the true airspeed (TAS) of the airplane, a typical airspeed
of 150 knots has been chosen to standardize the evaluation of these systems. However, the windshear
system algorithms may be sensitive to true airspeed, and high airspeed is critical for system update rate
evaluation relative to minimum detection time and low airspeed should be evaluated simply to show
that the system will in fact actually work at low airspeeds. Therefore, a limited number of runs are to
be evaluated at 120 KTAS and 200 KTAS. The 120 KTAS chosen is a typical minimum for lightweight
maximum flap takeoffs and landings at sea level standard day, and the 200 KTAS is a typical maximum
for heavyweight minimum flap operation at high altitude airports on a hot day.
2. Intervening Rain:
Intervening rain may adversely affect system performance. The system should be able to detect a
hazardous windshear with sufficient advance warning to be classified as a forward-looking system.
Since windshears can be contained in an environment with heavy rain, they should be detectable in
these conditions. Therefore, for testing sensor performance in intervening rain, some flight paths have
been oriented such that they pass through significant areas of rain prior to reaching the microburst
3. Pitch Angle:
The windshear detection system may have vertical look strategies that are fixed or variable. Since the
airplane's pitch angle is a function of excess thrust, configuration, and flight mode, the system should
perform satisfactorily over all expected circumstances. Radar ground clutter collection flights should
be conducted using the flight phases and characteristics specified in this section. All flight tests should
be conducted using sensor/airplane pitch angles critical for system performance.
4. F-factors at MUST-ALERT, below MUST-NOT-ALERT, or within MAY-ALERT:
Flight paths and NASA Windshear Data Sets have been chosen to provide FBAR events close to the
MUST-ALERT and MUST-NOT-ALERT boundary and within the MAY-ALERT criteria for several
microburst events. These events have been chosen to depict characteristics of the developing, peak and
decaying growth stages of these microbursts. The reflectivity, attenuation, relative strengths of the
vertical and horizontal windfield, symmetry (Data Sets 237, 349, and 614), etc., can change relatively
as a microburst develops and decays. These tests are to show that the system is insensitive to specific
modeled relationships. The F-factors for several of these cases are chosen to approximate the MUST-
ALERT F-factor. However, depending upon the threshold chosen for alert, the events located within
the MAY-ALERT criteria may not produce an alert. Also, several of these cases are to show that the
system is free from nuisance alerts when the windshear event is below the MUST-NOT-ALERT
5. Justification for NASA Windshear Data Set 111:
This is the best-documented accident case with data from a multichannel flight data recorder on the
Delta L-1011, which crashed in Dallas Texas August 2, 1985. It is probably one of the most studied
and debated atmospheric events in aviation history. Therefore, it is sensible that it be demonstrated that
a detection system will give advance warning of this event. This event represents the most severe, very
wet microburst likely to be encountered in service incorporating rain and hail . The event produced a
pronounced temperature drop.
6. Justification for NASA Windshear Data Set 237:
This event’s characteristics have been well documented from its penetration by the NASA 737 airplane.
This airplane incorporated radar and IR forward-looking sensors, a reactive windshear detection
system, and the event was correlated by a ground-based research Terminal Doppler Weather Radar
(TDWR). It is of moderate to strong intensity incorporating a wet core along with some intervening
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