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DO-253D Change 1
PVT Output Latency
The latency of the differentially corrected position, velocity, and time outputs, and their
associated protection level and FOM outputs, defined as the interval between the time of
the measurement and the time of applicability of the position, shall [LAAS-151] be less
than or equal to 500 milliseconds.
The data defining the differentially corrected position shall [LAAS-135] be output prior to
200 milliseconds after the time of applicability.
The LAAS equipment horizontal velocity output shall [LAAS-361] have an error that is
less than 10 m/s, (95th percentile), when the HDOP is normalized to 1.5 and the vertical
velocity output shall [LAAS-362] have an error that is less than 50 ft/s, (95th percentile),
when the VDOP is normalized to 3.0. These requirements shall [LAAS-363] be met under
the minimum signal conditions defined in Section 184.108.40.206.
1. The velocity accuracy requirements [LAAS-361 and LAAS-362] are design
requirements. These requirements do not imply that if the velocity FOMs at the
time of applicability are equal to or greater than 10 m/s and 50 ft/s for the
horizontal and vertical velocities respectively that the velocity should stop being
output or flagged invalid. Rather, the velocities should continue to be output and
the velocity FOMs (if provided as outputs) should continue to appropriately
characterize the velocity accuracy.
2. The test requirement in Section 220.127.116.11 defines an acceptable means of determining
the 95th percentile velocity accuracy.
Precision Approach Guidance Outputs
Note: Message processing depends on the type of equipment. Equipment that is
compliant with RTCA/DO-253B and earlier versions of this MOPS supports only
one type of approach service. Equipment built to this MOPS may be capable of
supporting multiple types of approach service. Consequently, in the following
sections message processing is defined for single Approach Service Type capable
equipment as well as multiple Approach Service Type capable equipment. Single
Approach Service Type capable equipment is by definition GAEC C and functional
requirements for GAST C are used at all times. Multiple Approach Service Type
capable equipment will have two states that are pertinent: the selected Approach
Service Type and the active Approach Service Type. The selected Approach
Service Type is the Approach Service Type indicated by the channel
selection/Approach Service Type selection of the approach. The active Approach
Service Type is the type of service that corresponds to the functional requirements
currently supported by the equipment.
FAS Data Block Selection and Confirmation
The PAN function shall [LAAS-110] select from the Type 4 message(s) the Final Approach
Segment (FAS) data set corresponding to the selected approach (Section 2.3.5). The PAN
shall [LAAS-111] validate the CRC for the selected FAS Data Block and only use it if the
FAS data block CRC, as defined in the RTCA/DO-246(), passes. The PAN function shall
[LAAS-112] output the corresponding Reference Path Identifier for the validated FAS Data
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