An Overview of Performance Based Navigation

How and why was Performance Based Navigation developed in aviation, how does it apply to business aircraft, and which phases of flight does it apply to today?

Traditionally aircraft navigated using a combination of the following sensors and independent systems:

• Automatic Direction Finding (ADF)
• Variable Omni Range (VOR)
• Distance Measuring Equipment (DME)
• Instrument Landing System (ILS) potentially with Autoland/autothrottle capability
• Very Low Frequency and Omega Long Range Navigation (LRN)
• Long Range Navigation – C (LORAN)
• Inertial Navigation System (INS).

Apart from inertial navigation, these systems required some form of ground infrastructure, requiring regular maintenance and verification testing. Several of them are now obsolete and others are in decline. Still in use today, built into current airspace design programs, and the most accurate for non-GPS navigation is DME.

System developers and airspace designers have created corridors, routes and procedures that rely on the performance of the aircraft to independently fly them, significantly reducing reliance on ground-based navigation aids. This has led to Performance Based Navigation (PBN) and a high degree of dependency upon satellite constellations to enable aircraft navigation.

Because of the threat of potential and realistic state-sponsored satellite interference, nations are ensuring aircraft can default to an alternative form of navigation. This uses dual Inertial Reference Systems (IRS) operating as independent laser navigation, and dual DME providing rho-rho navigation.

DME is ground station dependent but a worthwhile investment in placement and scheduled servicing, for national security reasons alone. Modern commonly deployed business aviation navigation system sensors, are:

1.    Global Positioning Systems (GPS)
2.    ILS, IRS and DME (less so VOR)
3.    Enhanced Flight Vision System (EFVS) for low visibility operations.

GPS, ILS, IRS and DME are blended or ‘switched between’ using a central Flight Management System (FMS). The FMS not only blends sensors into a single positioning source, but follows a pre-loaded flight plan. Employed to create its route algorithm are:

• Attitude
• Heading
• Air Data
• Fuel
• Radar Altitude
• Discrete inputs.

The FMS also develops and sends a single roll and vertical steering output to the Auto Flight Control Systems (AFCS).

The FMS displays its route and calculated information on Adaptive Flight Displays (AFD) or Electronic Flight Instrument System (EFIS). The Electronic Flight Bag may also be considered an aid to navigation as it is used for charts and other related features.

In many modern aircraft the navigation charts themselves, are offered as standard or optional to the installed Multifunction Displays (MFDs).

A Typical Large Business Jet Navigation System

General Description

On the assumption that most navigation is now conducted using GPS, this description of a typical system focuses on satellite navigation.

As of June 2022, there were 31 GPS satellites in orbit, of which 27 should be operational at any point in time, with a guarantee of reception of at least four at any point on Earth. The US GPS system is not the only satellite navigation network available.

Others include Russia (GLONASS); Europe (GALILEO EGNOS); China (BEIDOU); India (NAVIC); and Japan (QUASI-ZENITH).

In terms of operating frequency and accuracy, the Satellite networks are progressing through the evolution of L1, L2 and now L5, using GPS version III. In Business Aviation it is standard to find duplicate dedicated GPS receivers acting as sensors. The hardware and software level of these dictate the ability of the aircraft to operate on specific routes or fly satellite-based approaches.

Sensor information from IRS, DME and VOR is then blended, compared, or updated with the GPS to provide the flight crew with optimum position data.

As the central flight calculator, the FMS uses position information to compute against the preloaded flight plan to then direct the AFCS to maneuver the aircraft, keeping it on track and on time, both vertically and horizontally.

Phases of Flight

Under either Visual Flight Rules or Instrument Flight Rules (VFR/IFR), the aircraft navigation system guides the flight through several phases, including:

• Pre-flight and taxi to depart
• Take-off and climb out (SID)
• Level-off at cruise (Enroute)
• Domestic and/or International
• Terrestrial or Oceanic
• Terminal approach (STAR)
• Initial and final approach
• Land and taxi to the gate.

Depending upon the phase flown, the aircraft’s navigation systems will prioritize different sensors to utilize ground- and satellite-based services.

Having laid the foundation for our discussion of Performance Based Navigation, Ken continues his overview with a look at the navigational technology required in today’s crowded airspace. Continue reading in the AvBuyer June digital edition clicking the button below, or continue online via the Page 2 button…