Home' RTCA Documents for Review : DO-201B User Requirements for Navigation Data Contents ED-77A/DO-201BforOpenConsultation/FRAC
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The accuracy requirements captured in the DQR Tables 4-1 through 4-5 specify the
user requirements for the various data elements. Accuracies are stated for a 95 percent
confidence level with a 2 sigma deviation, and are believed to be achievable using cost
effective, modern, data acquisition techniques. The accuracies specified aim to ensure
that data errors have a negligible or acceptable contribution to the corresponding error
budget (certain applications may factor in the data accuracy margin).
The prior revision of this standard and the ICAO PANS-AIM data catalog were used as
starting points for the accuracy values. Values were reviewed considering industry
needs, practicality, and consistency with interchange formats. Additionally, many data
elements did not have accuracy values defined in reference material, so values were
assigned based on the needs of user applications.
The Accuracy column is the minimum accuracy to be achieved when determining the
required values during surveys or data acquisition. An “N/A” indicates that accuracy
does not apply for the data element, typically because it is not a numerical value. ICAO
values are shown in brackets “” when they differ from the industry requirement.
It is acknowledged that it is not always possible to assess that the data published by
States meets the specified accuracy requirements, for a number of reasons, including
but not limited to:
Values different from geographical value (e.g., RW Y length being restricted due
to operational considerations)
Uncertainty on the actual initial way to survey the data (e.g., ARP)
When the accuracy cannot be assessed, the accuracy requirement is not applicable.
This does not alleviate upstream data chain participants from adhering to accuracy
requirements for data origination.
There are also cases where the data elements are derived from various calculations
and processes and declared by the originator, and for which no accuracy requirements
could be identified in existing standards. The corresponding data elements are labelled
in the DQR tables as “DV” (Declared Value), followed by the expected minimum
resolution of the data in parenthesis.
Resolution is defined as the number of units or digits to which a measured or calculated
value is expressed and used [ICAO Annex 15]. Resolution shall [NAV-R014] be
sufficient to support the accuracy requirements. Resolutions should [NAV-D018] be at
least one or two orders of magnitude more granular than the accuracy requirement. For
example, to support an accuracy requirement of 1m, the resolution is expected to be 0.1
m or higher.
A resolution value for those data elements with numerical accuracy requirements is not
specified as it is based on the principle that resolution shall [NAV-R015] support the
accuracy of the data.
Historically, loadable format packing may use data resolutions that are not sufficient to
ensure the accuracy of the values have been maintained (e.g., due to truncation or
rounding of the original value in order to fit within an allocated number of bits for the
binary format). Downstream (user) implementations do not necessarily relieve upstream
data chain participants (suppliers) from meeting the stated data quality requirements.
For those data elements that are calculated values for which an accuracy requirement
exists, the accuracy of the calculated value is limited by the accuracy of the least
accurate value used in the calculation (for example, the position of a final approach fix
is based on a bearing and distance from a runway threshold position). It was not always
possible to take into account the accuracy of variables upon which a calculated value is
dependent. In such cases, listed values were determined to be reasonable for the
considered applications. The published resolution for a calculated value should [NAV-
D019] be consistent with the resolution(s) of the input(s) used in the calculation.
Whenever it is necessary to convert any units of measurement, the conversion values
specified in ICAO Annex 5 should [NAV-D020] be used. This will ensure the
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