Home' RTCA Documents for Review : DO-220A Change 1 Contents Appendix B
DO-220A Change 1
© 2018 RTCA, Inc.
Takeoff – “near microburst” scenarios: This windshear hazard located such that the airplane is in the
headwind outflow closely matches the reference accident cases and would reduce the system’s
capability to determine the relative velocity change or relative temperature difference across the
outflow. This is because the airplane is essentially located in a portion of the increased headwind to
Takeoff – “far microburst” scenarios: This windshear hazard located such that its leading edge is at 3.0
nm is to show that the system will issue a windshear warning prior to takeoff.
13. Justification for Takeoff Gear-Up Height Flight Scenario:
This scenario represents the next stabilized phase of flight and is significantly different from brake
release. This case will evaluate the system’s capability to scan in the most nose-down direction relative
to the airplane.
Data Set 3 was selected because if the microburst is not detected, the pilot may mistakenly take off into
the windshear because of its benign appearance due to being dry. Data Set 5 is large enough to be a
threat. Due to its benign appearance and due to being dry, it would be a challenge for the crew to detect
without a windshear detection system.
Takeoff Gear-Up Height – “far microburst” scenarios: The windshear hazard leading edge at 3 nm from
brake release puts the event at approximately 1.5 nm from the gear up point. This is the distance
recommended for the crew to be given a windshear warning in flight.
14. Justification for Straight-In Approach Flight Scenario:
This scenario represents the typical nominal operational approach condition. The leading edge of the
hazard is chosen at the middle marker. This assures that when the system alerts are enabled at 1200 feet
AGL that approximately four miles to the hazard are available for system detection and display
evaluation. In this case, the hazard is located only about 10 seconds from the runway threshold. It was
considered sensible for evaluation to be able to compare the system’s performance for windshear
detection over a range of windshear events while holding other variables more or less fixed. The
straight-in approach provides the longest stabilized flight phase for this evaluation, and therefore has
been chosen to evaluate all windfield models.
15. Justification for Curved Approach Flight Scenario:
This scenario assesses the system performance during an approach in which the airplane, initially with
its flight path offset from the windshear turns into it while lining up on the localizer. Having the leading
edge of the windshear hazard located at the point where the airplane intercepts the localizer represents
the worst case for advanced warning. The system should have enough azimuth scan to give at least 10
seconds advanced warning as the airplane turns into the hazard.
Since this evaluation is only to assess the system’s ability to detect windshears as the airplane turns into
them, only a limited number of windfield models need to be evaluated. Data Sets 3, 5, and 6 have been
chosen as representing a reasonable sample with F-factor values close to the system MUST-ALERT
boundary. During the Data Set 3 event, one of the airplanes that actually encountered this windshear
made a turning approach into it. This then forms a historical basis for demonstration. Data Set 5 is a
small microburst that will stress the system’s ability to detect the windshear’s outflow in a timely
manner since the airplane is initially approaching offset from it. Data Set 6, being highly asymmetric,
will stress the system’s ability to accurately calculate the event’s F-factor since the microburst’s
perspective will be constantly changing as the airplane turns into it.
Since it is assumed that a higher initial lateral offset from the windshear is the critical condition, only
the 200 KTAS case has been picked. This will produce an initial lateral offset of 7600 feet for a standard
rate (3 degrees / second as limited by 25 degrees bank angle) turn to intercept.
The altitude of 1000 feet was chosen to assure that the windshear detection system alerts are active.
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