A guide to navigational terminology

 - October 18, 2006, 7:57 AM

Eurocontrol provided a short guide to RNP and Rnav concepts and terminology as a primer for delegates.

Area navigation (Rnav) performance levels, capabilities and functionalities are detailed in the minimum aviation system performance standards (Masps), RTCA DO-236B and EUROCAE ED-75B. While it is unlikely that all the Masps functionalities will be required, it is possible that some not included in the Masps toolbox will be needed.

The decision about which functionalities are necessary for the next step in terminal and en route navigation applications and the question of whether additional functionalities are needed depend on operational requirements and on the cost-benefit equation.

The baseline in any RNP choice includes horizontal navigation accuracy of one nautical mile or better, containment continuity and containment integrity and availability. Additional options include the ability to execute a series of defined maneuvers or procedures: radius-to-fix legs (equivalent to fixed-radius turns); fixed-radius transition; required time of arrival; parallel offset; and–not defined in the Masps–vertical containment and 4-D control.

Rnav systems can be stand-alone or incorporated in a flight management system (FMS) and have various levels of sophistication. The more sophisticated the system, the more functionalities it has and the more benefits it offers, but not all sophisticated Rnav systems and FMSs share the same functionalities.

The level of sophistication required of an Rnav system or FMS is reflected in the certification standard and operational approval. In the 43-nation European Civil Aviation Conference (ECAC) area these standards and approvals were covered in Joint Aviation Authorities temporary guidance leaflets.

In the future, when the European Aviation Safety Agency (EASA) assumes responsibility for operational regulation, these documents will be known as EASA-acceptable means of compliance. The U.S. has a similar approach.

A navigation application constitutes the link among the system certification and operational approval, the navaid infrastructure on which it depends and the airspace concept into which it fits. A navigation application can have its own designation, which is not necessarily the same as that of its supporting certification/operational approval. In the ECAC, for example, basic area navigation (B-Rnav) is the en route navigation application based on the certification/operational approval in TGL No. 2.

B-Rnav has been mandatory in ECAC en route airspace since 1998; its certification standard, TGL 2, is not particularly demanding. Precision Rnav (P-Rnav), a terminal navigation application in the ECAC, has a more demanding certification standard (TGL 10) that is being introduced in some terminal airspaces this year.

U.S. terminal and en route navigation applications are known as Rnav Type A and Rnav Type B, respectively. But none of these ECAC or U.S. terminal and en route navigation applications is RNP.