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DO-253D Change 1
Note: The interface for the minimum equipment is specified with angular deviations that
are intended to mimic current ILS outputs. This is done to facilitate integration of
LAAS equipment into existing airplanes with a minimum of disruption.
The operational goal of LAAS as specified in this document is to augment GPS to satisfy
the requirements to support all categories of precision approach operations, guided takeoff,
area navigation in the terminal area, and automatic dependent surveillance. It is also
anticipated that LAAS will support surface guidance, not limited to the runway, and other
operational needs in the future. This document will be updated if necessary as requirements
to support these further operations are matured.
The LAAS signal provides the augmentation to GPS to obtain the required performance
for the operations supported. The operations supported will be dependent on the user's
equipment, the LAAS Ground Facility (LGF), and the capabilities of the airplane
GBAS Approach Service Types
A LAAS ground station may provide multiple types of approach service simultaneously to
many users who may have different operational objectives. To facilitate interoperability
and consistent, predictable performance, the airborne and ground subsystem performance
requirements are organized into matched sets that are intended to be used in conjunction.
These matched sets of performance and functional requirements are collectively referred
to as GBAS Approach Service Types (GAST). The specific requirements for the Ground
and Airborne subsystems are then organized by Ground Facility Classifications (GFC) and
GBAS Airborne Equipment Classifications (GAEC). A discussion of the relationship
between Approach Service Types and Facility Classifications is given in Appendix I. The
requirements in this MOPS for such approaches are organized according to the GAEC
and/or by the GAST being supported by the equipment.
Notable Changes from Previous Version
Version C of the MOPS incorporated changes relative to RTCA/DO-253B and previous
versions that altered or augmented the operational use of LAAS in some ways that are
important to note:
The requirement to compute and output a vertical protection level for the
positioning service has been eliminated. The horizontal protection level has been
retained as a minimum output. This change was implemented to allow the
maximum usable distance, Dmax, to be set to a much larger value.
Velocity accuracy requirements and optional velocity figures of merit have been
specified that will allow, for example, integration with position and velocity
A new Approach Service Type was added and intended to support Category II/III
operations. The service type includes several unique additional requirements and
a different approach for allocation of performance between air and ground
VDB authentication protocols have been added as a required capability for
avionics supporting the new Approach Service Type.
GPS tracking constraints for receivers that use Double Delta delay lock loop
discriminators have changed since last version.
Airborne equipment classifications have been added as described in Section 1.3.1.
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