EUROCAE ED-144 PDF

PURPOSE, SCOPE AND OVERVIEW

This document contains high-level performance requirements for a Ground Based Augmentation System (GBAS), as part of the Global Navigation Satellite System (GNSS), to support CAT I, II and III precision approaches and landing.

Primary performance parameters are accuracy, integrity, availability, and continuity. The document also defines some additional system level performance requirements. These parameters are specified at the system level in this document but are not allocated to the major subsystems. Because it only addresses high-level requirements without subsystem allocations, this document does not replace or update EUROCAE ED-95. It is anticipated that a new, complete MASPS covering precision approach applications will not be completed until the high-level requirements are agreed at ICAO level and the implementation of GBAS CAT I has progressed further.

The specifications of this document have been derived from ILS standards in order to simplify aircraft integration and certification, without regard to specific GNSS elements and associated performance. Hence, they do not imply a specific architecture, nor do they dictate the use or combination of specific GNSS core constellation elements. However, since Galileo signals will be available in the anticipated timeframe of GBAS CAT III implementation, it is expected that GBAS will take full advantage of both GPS and Galileo signals on all frequencies usable for aviation in order to provide a robust and reliable service. This necessitates that CAT III operations remain viable even in a single frequency, single constellation fall back mode. Future architectural development and refinement of associated requirements will have to take these considerations into account.

The specifications in this document also do not impose any supplemental restrictions on aircraft FTE performance beyond those existing in the ILS standards.

This document is not expected to be implemented by regulatory documents; it is intended to be a tool to support the further development of standards for GBAS to support all categories of precision approach and landing. The methodology used to develop the Category II and III performance requirements is identical to that used previously for Category I. This methodology derives the requirements from the ILS standards with additional validation provided by aircraft certification requirements. In particular it interprets the alert limits as the largest navigation system error which can be experienced without an alert, where the probability of a navigation system error larger than the alert limit is defined by the integrity requirement. The resulting requirements are generic and no credit is taken for system monitors which may limit the magnitude of errors for some failure modes. This may result in more stringent navigation system requirements than those derived for specific systems taking these monitors into account.

Chapter 2 of this document provides a system description and definitions needed to understand the requirements stated in the remaining sections. It describes typical equipment applications and operational goals and forms the basis of the specifications in Chapter 3.

Chapter 3 contains the minimum system performance specifications for the complete system, including requirements to support CAT I, II and III operations.

Appendices A through D are informative and contain rationales for the requirements and allocations given in section 3 on, respectively, accuracy, continuity, integrity and availability.