FAA moves forward on RNP implementation

 - May 7, 2008, 5:21 AM

In late summer, Jeff Williams, manager of the FAA’s newly established required navigation performance (RNP) program office, briefed a government/industry specialist group on the agency’s implementation for a nationwide public RNP plan. Commencing next year, the plan foresees an initial two-phase, five-year program, with its first phase aimed at gathering together as many participants as possible, with general aviation especially being targeted.

RNP defines the ability of an aircraft’s navigation equipment to achieve a specified level of lateral accuracy for 95 percent of the time. For example, RNP-10–typical of oceanic operations–should keep the aircraft within ±10 nm of its required track.

But RNP can go down to as low as 0.02, or ±35 meters, typical of the accuracy required for ILS, MLS, LAAS and the future WAAS-based approaches. With a certified RNP capability, therefore, more airspace “tunnels” can be safely accommodated, with significant capacity increases.

But the tighter the RNP requirements, the more demanding is the onboard avionics systems certification, so that an aircraft’s RNP capabilities become a graded admission ticket to various RNP Rnav designated routes. For example, the
integrated IRS/GPS/FMS/autopilot/ EGPWS avionics package required to achieve RNP-0.11 in Alaska Airlines’ Boeing 737s is hugely expensive compared with that required to meet RNP-10.

Four Performance Levels

The FAA proposes to adopt four performance levels: RNP-2, RNP-1, RNP-0.3 and RNPs of less than 0.3. (The RNP-0.02 mentioned earlier is an oddity here, since it applies only to precision approaches and nowhere else.)

But Hooper Harris of FAA flight standards stressed that while the program’s first phase, using RNP-0.3 as a baseline, was aimed at involving as many users as possible, at their option, RNP compliance will not be mandatory.

Phase 1 (FY 2003 and 2004) covers:

• Public RNP-0.3 approach procedures, requiring RNP-certified GPS, DME/DME/IRS or GPS/ IRS. A single, non-WAAS, IFR certified C-129 GPS receiver (with VOR/DME backup) might meet this requirement in Part 91 aircraft.
• Public RNP-0.3 parallel approaches, using similar equipment.
• New RNP approach TERPS.
• Special procedures using RNP-0.3 or lower values.
• New arrival and departure TERPS covering RNP-2 Stars and DPs.
• New en route TERPS covering RNP-2 (eight-nautical mile centerline separation) where beneficial.

Phase 2 (FY 2004 to 2008) covers:

• Public RNP-0.3 application of the FAA’s airline special aircrew and aircraft authorization required (RAAAS) rules.
• Lower RNP values.
• FMS RNP waypoint turns.
• RNP-1 arrival and departure procedures.
• RNP-1 en route applications.
• Optimization of National Airspace System route structures.

Developing a ‘Road Map’

The program office is now developing an FAA/industry road map, assembling a user avionics inventory, identifying key issues and defining performance yardsticks. Williams intends to adopt a conservative approach, with attainable goals, through close coordination with the FAA’s certification and flight standards groups, in addition to the FAA/industry Terminal Area Operations Aviation Rulemaking Committee (TAOARC) and with ICAO and Europe’s Joint Airworthiness Authorities (JAA).

The objective is to demonstrate that RNP will bring benefits not obtainable using current strategies. A detailed Phase 1 program plan is being developed with user groups, including the selection next year of five high-visibility projects, including at least one general aviation RNP-0.3 approach.

A public briefing document describing RNP’s benefits and the FAA’s implementation plan will be published early next year, as will guidance material for FAA FSDO staff to ensure consistency in FAR Part 91 equipment and installation approvals.