Home' RTCA Documents for Review : DO-253D_Change1_FRAC Contents Appendix J
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DO-253D Change 1
If the maximum range error, maxER, is known, and if a maximum vertical error can be
tolerated by the aircraft, then the user specified geometry screening limit can be derived by
dividing maxEV by maxER. This can be similarly accomplished for the lateral case.
Geometry Screening, Airworthiness, and Airplane Performance
In this section, the general equations for touchdown performance are examined and their
applicability to the three assumed airworthiness requirements is shown. First, the general
expression for probability of an unsuccessful landing is described, then applicability to the
three airworthiness criteria is discussed. In each case, example uses of geometry screening
limits to meet the assumed longitudinal touchdown airworthiness requirements are
discussed. Note that this same technique may be used to show airworthiness for the lateral
touchdown and other performance parameters.
Longitudinal touchdown distribution is a driving requirement in terms of airplane
performance and airworthiness; however, it is not the only requirement. Methods similar
to those discussed in this appendix may be applied to additional performance parameters
in order to determine compliance with the other dimensions of the airworthiness
requirements, such as lateral touchdown, bank angle, etc., in as much as they are dependent
on the NSE (both fault-free and faulted). For the remainder of this appendix, the
longitudinal touchdown case will be described for example.
Let the following variable describe a probability density function for the location of the
touchdown point on the longitudinal axis, x, of the runway for the nominal, fault-free
This distribution is typically determined as part of the airplane certification process by
performing a high-fidelity landing simulation for a particular airplane and autopilot design
using a standard GBAS signal model to represent the fault-free NSE for the receiver being
used, and using standard models for environmental effects, such as wind. For each
airworthiness requirement, this distribution may be defined differently.
Then, the generalized probability that a landing is unsuccessful, PUL, is the integral of the
touchdown distribution about the region defined as unsuccessful for the particular
As explained in the next three sections, the unsuccessful region and the touchdown
distribution are treated differently for each airworthiness requirement. Next, the regions of
success and treatments of TSE for each of the three airworthiness criteria are discussed.
Finally, the required geometry screening as a function of airplane performance is described
as an example for each of the three criteria.
The nominal condition for the longitudinal touchdown case requires that
PUL < 10-6
for a land short limit of 200 feet and, separately, for a land long limit of 2700 feet. The
touchdown distribution used to form PUL for the nominal condition is required to include
the effect of all influencing parameters varied according to their expected distributions.
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