Are You Ready for PBN? (Part 3)

Multiple operators are upgrading to Performance Based Navigation (PBN) capability for various phases of flight, notes Mario Pierobon. This month we cover a navigation specification that’s of significant value to business jet operators: the RNP approach...

As a macro-category, RNP specification includes two different types of approaches. These include:

• RNP approach operations down to LNAV (lateral navigation) and LNAV/VNAV (lateral navigation/vertical navigation) minima; and
• RNP approach operations down to LP (localizer performance) and LPV (localizer performance with vertical guidance) minima.

RNP approach operations to LNAV and LNAV/VNAV minima rely on lateral navigation guidance provided by a Global Navigation Satellite System (GNSS) and have vertical guidance provided by a conventional barometric system.

RNP approach operations to LP and LPV minima, meanwhile, rely on lateral navigation guidance provided by a satellite-based augmentation system (SBAS).

An SBAS provides an optimized, highly accurate, GNSS signal.

LPV approaches have, in addition, vertical guidance that is also SBAS supported. LPV approaches are classified to be ‘localizer performance with vertical guidance’ because they closely mimic conventional ILS approaches down to decision altitudes of up to 200 ft.

It should be noted that at some airports it may not be possible to publish an LPV approach due to obstacles and/or terrain along the desired final approach path, or the inability of the SBAS to provide the desired availability of vertical guidance. In these instances the regulatory authority may instead elect to provide an LP approach based on the lateral performance of the SBAS only.

Gaining Momentum

LPV and, where not available, LP approaches are gaining momentum in Business Aviation. The high accuracy of SBAS optimized GNSS signals, together with the availability of the aircraft equipment needed to perform LPV and LP approaches (e.g. a GNSS SBAS sensor) in newer generations of business aircraft, are leading operators to apply for the operational approval needed to perform this kind of approach.

In order to be LP and LPV approved, an operator first needs to familiarize itself with the documentation its national aviation authority uses to assess readiness to perform LP and LPV approaches.

In the US, the FAA has issued airworthiness criteria for GNSS equipment and systems that are eligible for LP and LPV approaches in Advisory Circular (AC) 20-138(c and d). In Europe, EASA has developed certification material for airworthiness approval and operational criteria for LP and LPV approaches in Acceptable Means of Compliance (AMC) 20-28 consistent with the FAA material. These two sets of criteria are also harmonized as a global standard in Volume II, Part C, Chapter 5, Part B of ICAO PBN Manual (Document 9613, advanced fourth edition 2013).

LP and LPV certification materials contain requirements that are of interest to operators with regard to aircraft eligibility, operational approval, aircraft requirements, operating procedures, training and navigation database.

Operator Focus?

Airworthiness requirements are not normally a major concern for operators, unless they elect to retrofit an older aircraft with equipment that allows them to meet the airworthiness requirements associated with LP and LPV approach operations. The service bulletins to be implemented to meet LP and LPV capability can easily cost several hundred thousand US$, thus thorough economic considerations need to be given to the cost of installing the required equipment versus the anticipated frequency of operating to airports without ILS approaches.

Operators should focus on PBN procedures, because that is the area where change must be managed.

Operating procedures need to be developed for pre-flight planning; the verification of augmented GNSS availability; tasks to be performed prior to commencing the LP/LPV procedure; tasks to be performed during the procedure; general operating procedures; and contingency procedures.

It should be noted that the certification materials only provide for high level requirements that need to be incorporated into the standard operating procedures of the operator and documented within its operations manual. The activity of developing operating procedures requires a sophisticated task analysis and the identification of a standardized way of performing a task. This standard should be documented in the operations manual in the ‘WHAT-WHEN-WHO -FOLLOWED BY’ format, without any ‘copy-paste’ from regulatory material.

‘What-When-Who-Followed By’

The ‘WHAT-WHEN-WHO -FOLLOWED BY’ format requires that every specific task making up a procedure is detailed in terms of:

• WHAT action is needed;
• WHEN it is needed;
• WHO needs to perform this; and
• What the given task is to be FOLLOWED BY.

PBN benefits operators in terms of airport access, reduced flight time and improved fuel consumption. It is important that operators fully familiarize themselves with the PBN concept, understand the large availability of navigation specifications, and comply with the operational requirements needed to implement the PBN operations they elect to adopt.

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