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FAA's plan for the retention of legacy navaids in the future.

FAA will decommission 497 VORs by 2020. Remaining VORs will form the Minimum Operational Network or MON. Decisions made today concerning the ground based legacy navaids being kept will determine the equipment we need to fly in tomorrow's airspace.

By Bill Gunn
ATP/CFII. Compliance Mgr,
State of Texas Aviation Division


GLS 04L at Newark. This approach requires the aircraft be WAAS and GBAS (LAAS) capable This is one of the approaches affected by loss of signal to the GBAS antennas on the airport.

Most pilots and system users think of the FAA's NextGen transition plan in terms of GPS, WAAS and ground based GPS augmentation systems just now being placed at hub airports in the USA.

There is another side to the NextGen plan that considers the requirement for Alternate Position, Navigation and Timing (APNT) systems in the National airspace System (NAS).

Looking at the GPS signal problem case at EWR (Liberty, Newark NJ)

Perhaps one ominous indicator of the need for an APNT plan is the unintended consequence to the Ground Based Augmentation System (GBAS or LAAS) installed at Newark Liberty. Due to a multitude of requirements the only location these GBAS antennas could be installed at EWR was east of runway 22L within a few hundred feet of the New Jersey Turnpike.

It turned out that certain users on the Turnpike had equipped their commercial vehicles with low power GPS jammers apparently to deny a GPS position to parties that might be interested in the location of that commercial vehicle. The unintended consequence was a random but persistent denial of the GBAS signal required for the GPS Landing System (GLS) approaches to EWR. Only the GBAS signals were disrupted. The satellite GPS and WAAS signal integrity was never compromised.

This odd situation has been rectified. However the lesson is not missed. GPS is vulnerable to inadvertent or intentional signal compromise. The Course Acquisition (C/A) signal currently operating on the single civil L1 frequency from the GPS satellites 14,000 miles in space to your aircraft and ground receivers is very weak. Cleanly received and amplified this signal is the basis for all GPS based operations in the NAS. FAA is working on implementation of a second civil C/A signal, L5, but acknowledges that inadvertent or intentional loss of GPS signals means that alternate means of navigation is critical to the NAS.

FAA published a Notice of Proposed Rule Making (NPRM) in late 2011 soliciting input for the Minimum Operational Network (MON) proposal. Several hundred comments were received concerning the development of an alternate positioning, navigation, and timing (APNT) plan as part of NextGen.

Makeup of the APNT solution

Alternate Positioning, Navigation and Timing (APNT) coverage zones within the NAS (National Airspace) system.

FAA plans to transition from defining airways, routes, and procedures using VOR and other legacy navaids towards an NAS based on Area Navigation (RNAV) everywhere and Required Navigation Performance (RNP) where beneficial. Such capabilities will be enabled largely by GPS and WAAS.

The FAA plans to satisfy any new requirements for Category I instrument landing operations with WAAS Localizer Performance with Vertical guidance (LPV) procedures. The network of existing ILSs will remain to provide alternative approach and landing capabilities to support continued recovery and dispatch of aircraft during any GPS outages.

This transition is consistent with the NextGen plan and the NAS enterprise architecture, which is the design of all elements of the NAS and how they interact. The FAA plans to retain an optimized network of DME stations and a MON of VOR stations to ensure safety and continuous operations for the high and low altitude enroute airspace over the conterminous USA and terminal operations at what has been deemed the core 30 airports.

Core 30 airports are those with significant activity serving major metropolitan areas and also serve as hubs for airline operations.

The core 30 airports are:
1 ATL Hartsfield-Jackson Atlanta Intl
2 BOS Boston Logan Intl
3 BWI Baltimore/Washington Intl
4 CLT Charlotte Douglas Intl
5 DCA Reagan Washington Natl
6 DEN Denver Intl
7 DFW Dallas/Fort Worth Intl
8 DTW Detroit Metro Wayne Co
9 EWR Newark Liberty Intl 10 FLL Ft Lauderdale/Hollywood Intl
11 HNL Honolulu Intl
12 IAD Washington Dulles Intl
13 IAH George Bush Houston Intl 14 JFK New York John F Kennedy Intl
15 LAS Las Vegas McCarran Intl
16 LAX Los Angeles Intl
17 LGA New York LaGuardia
18 MCO Orlando Intl
19 MDW Chicago Midway
20 MEM Memphis Intl
21 MIA Miami Intl
22 MSP Minneapolis/St. Paul Intl
23 ORD Chicago O`Hare Intl
24 PHL Philadelphia Intl
25 PHX Phoenix Sky Harbor Intl
26 SAN San Diego Intl
27 SEA Seattle/Tacoma Intl
28 SFO San Francisco Intl
29 SLC Salt Lake City Intl
30 TPA Tampa Intl

Additionally, FAA is developing a concept of "Safe Harbor" airports throughout the NAS beyond these core 30 airports.

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