Performance Based Navigation: Technology & Integration

Having provided an outline of Performance Based Navigation (PBN) in Business Aviation, Ken Elliott explores aspects of technology and integration in today’s aircraft, while highlighting the basis of different navigation operations.

Ken Elliott  |  28th June 2023
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    Ken Elliott
    Ken Elliott

    Ken Elliott is a veteran with 52 years of aviation experience, focussed on avionics in General and Business...

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    The sensors used for navigation in aircraft determine the performance capability to meet limitations set for crowded airspace and popular flight corridors. So what are the requirements today?

    One technology requirement is the continuous monitoring of the sensors to ensure the derived positioning remains within allowable limits. Modern flight management includes aircraft performance and tracking to complex navigation database profiles.

    Different manufacturers use different /methods to update their FMS database, for both tailored performance and constantly updated airspace & routing information.

    Typically, flight departments will have an access point to accept the database updates that will then distribute the information into computers over ethernet.

    Apart from some analog discretes, the remainder of the system data intranet is over a proprietary bus. Today, navigation selection between different sensors, FMS computers and displays, has moved from analog switching to either cockpit push button or touchscreen methodology.

    Integration of Navigation Equipment in Modern Business Aircraft

    To meet the stringent demands of complex airspace operations, today’s FMS handles a multitude of tasks. This calls for a highly integrated cockpit. 

    Beginning with a host of external antennas where the real estate is limited and access not easy, the complete navigation system installation has moved from dedicated black boxes as Line Replacement Units (LRUs), to a modular concept of caged circuit cards, one for each navigation process.

    Rather than have hidden boxes throughout the fuselage, easy to access card cages improve reliability and lessen weight and maintenance.

    Smaller aircraft may find most of the navigation tasks are accomplished within the cockpit itself, while for larger aircraft there is still a need to use remote hardware – providing input and output – to and from the cockpit.

    Either way, the design of navigation equipment in more recent aircraft has shifted to common, baseline platforms within each manufacturer’s brand, allowing for software updates to take care of new features and capabilities.

    Operation RNAV and RNP: Most navigation operations are based on either Area Navigation (RNAV) that preceded the PBN concept, or Required Navigation Performance (RNP) – depending less on ground navigation beacons – and on ATC radar vectoring or altitude and speed assignments.

    Waypoints used in route calculations are mostly points in airspace and not directly over existing beacons. RNP operations add continuous Onboard Performance Monitoring and Alerting (OPMA) taking the place of ATC radar monitoring.

    These flights are self-tracked within designated 3D routes, maintaining required separation and corridor containment. The world is completely transitioning from RNAV to RNP

    The following specific PBN performance designations appear on regularly updated aeronautical charts that may be embedded in cockpit electronics for on-screen viewing. The numerical designation of each is +XNM from centerline containment for 95% of the total flight time, for enroute and terminal operations.

    • RNAV 1: Used for Departure Points (DP) and Standard Arrivals (STAR). Either US-RNAV or European P-RNAV (Precision) designation. The US uses GPS or DME/DME and Europe accepts DME/VOR
    • RNAV 2: Used for enroute operations, such as T or Q routes
    • RNAV 5: Used for Europe’s B-RNAV
    • RNAV 10: Used for Oceanic operations.

    For RNP, the numerical designation of each is +XNM from centerline containment for 95% of the total flight time for enroute and departure, plus no more than double that deviation for 99.999% of the time. For approaches, the containment limits are called out below. The following all require OPMA for reliable performance.

    • RNP 4: Used for Oceanic and FANS 1/A equipped aircraft. Lateral 23nm and longitudinal 30nm aircraft separation is maintained, reporting every 12 minutes over FANS ADS-C.
    • RNP 2: Used for enroute domestic, offshore, oceanic, and remote continental regions and some remote Continental routes where infrastructure is sparse.
    • RNP 1: Used for Optimum Profile Descents (OPD), SIDS and STARS.
    • A-RNP: An internationally harmonized standard for all phases of flight, including RNP-1, RNP-2 and RNP Approaches, but not RNP-AR. The procedure includes transitioning, and features include:

    -    RF Legs or curved paths used in terminal and approach procedures
    -    Parallel offsets left or right of centerline route
    -    Scalable RNP, an automated cockpit display scaling of RNP value
    -    Three other features listed below under PBN and Flight Management.

    • RNP 0.3: Used primarily by rotorcraft in terminal and non-final approach segments of the flight. Turns capability needs to be within the aircraft FMS system.
    • RNP APCHSpecifically used in the approach segment of a flight. Limit: 0.3nm to 1.0NM for 95% of the approach segment.
    • RNP AR APCH (and DP): Specifically, Authorization Required (AR) approaches or departures, where scalability and RF turn capability are both crucial. Special pilot training and equipage requirements must be met to fly these approaches. Limits: 0.1nm to 1.0nm.

    APV, LP, LPV and Steep Approaches

    PBN includes approaches considered RNAV with vertical guidance (APV). They may include the use of VNAV/LNAV and an Instrument Landing System (ILS).

    If approaches incorporate the use of Satellite-Based Augmentation System (SBAS), then the approach is considered either Lateral Path (LP) or Lateral Path Vertical (LPV). The technology used is termed Wide Area Augmentation Systems (WAAS), or EGNOS in Europe.

    With any approach Decision Altitude is limited to 200ft, WAAS approaches differ from Local Area Augmentation System (LAAS) approaches – now termed Ground-Based Augmentation System (GBAS) – that can use lower minimums.

    WAAS approaches are mostly used at airports without ILS approaches and are popular with business aircraft. The onboard GPS/FMS is considered WAAS LP/LPV capable and there are currently 4,114 LPV at 1,995 airports, and 736 LP approaches at 538 airports.

    Note that apart from CAT II or CAT III ILS, business aircraft may operate to below 200ft approach minima using approved Enhanced Flight Vision Systems (EFVS) that include Head-Up Displays (HUDs).

    Some approaches are Steep Approaches that require the ability of the aircraft’s navigation systems to track a greater angle of descent than 4.5° (Glideslope is typically 3°). London City Airport (LCY) is one such approach. 

    Learn how navigation implementations involving hardware are certified around the world. Continue reading in the AvBuyer June digital edition clicking the button below, or continue online via the Page 3 button…

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