Home' RTCA Documents for Review : DO-220A Change 1 Contents Appendix A
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DO-220A Change 1
rain. Evaluation of the system’s performance against this model will provide a traceable link between
airborne and ground TDWR measurements.
7. Justification for NASA Windshear Data Set 349 and 351:
This event is a well-studied incident case and represents a multiple microburst event. The model
includes low to moderate reflectivity microbursts, a severe low reflectivity microburst, wide and narrow
downdrafts with asymmetry. It expands into a macroburst with embedded microbursts with multiple
downdraft centers within one of the microburst cores. This model is included in order to stress the
detection system to determine if stronger events may be hidden by closer weak wet microbursts. Also,
the asymmetry will stress the algorithm calculating the F-factor. This is to be shown by penetrating the
model using several headings.
8. Justification for NASA Windshear Data Set 436:
Microbursts can penetrate a temperature inversion stable layer causing a non-typical temperature
signature. This case also produces a high F-factor in a small area with a shallow outflow. These
characteristics will stress the detection system’s assessment of hazard in terms of range-bin size and
azimuth averaging or other nuisance rejection schemes.
9. Justification for NASA Windshear Data Set 540 and 545:
This model will determine the system’s ability to detect “dry” microbursts. The second pulse very dry
5 dBZ core event was chosen as a compromise between wet and extremely dry (less than 0 dBZ core)
but of low probability, and the technology needed to not miss such events at the 10-5
10. Justification for NASA Windshear Data Set 614:
Microbursts are not necessarily symmetric; therefore, the assumption that along track radial outflow is
directly related to downflow is only an approximation. This windfield model will stress the system’s
ability to assign a proper F-factor to microbursts that are highly asymmetric when penetrated every 45
degrees of azimuth.
11. Justification for NASA Windshear Data Set 727:
Convection activity gust fronts can produce hazardous windshears. Even though gust fronts can be
safely penetrated while in flight, since the tailwind energy loss is preceded by a headwind energy gain,
if they occur during the takeoff roll they can be considerably more hazardous. This occurs if the
headwind increase is encountered during the takeoff roll before VR. As soon as the airplane is airborne,
the rapid loss of the headwind shear of the gust front can then pose serious performance shortfalls that
have not been offset by the earlier headwind increase. This model is to determine that the system can
also detect these events if their F-factor is above the hazard threshold.
12. Justification for Aligned for Takeoff Flight Scenario:
The takeoff scenario is to evaluate conditions similar to those existing in the Continental accident in
Denver on August 7, 1975 and the Pan Am accident in New Orleans on July 9, 1982. This evaluation
will also determine the system’s ability to scan ahead using update rates high enough to provide the
crew with timely information on hazardous windshear conditions prior to brake release.
Data Set 1 was selected since it would pose considerable hazard to the airplane even at the most nose
down direction relative to the airplane. The specific microbursts of Data Set 3 and Data Set 4 were
selected because if not detected, the pilot may mistakenly take off into the windshear because of its
benign appearance due to being dry. Additionally, Data Set 4 was selected as being critical for detection
at close range because its shallow outflow and small diameter would not necessarily pose much of a
threat during later stages of the takeoff; to require its detection at 3.0 nm from brake release was
considered unnecessarily severe in evaluation of the system. Data Set 7 (gust front) was selected since
the takeoff is the critical flight phase for hazardous effects from this event.
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