FAA History Lesson -- June 2

From the FAA Historical Chronology, 1926-1996...

”Jun 2, 1994: Administrator Hinson announced that FAA would halt further development of the Microwave Landing System (MLS) for use under the more difficult visibility conditions rated Category 2 and 3 (see Jun 15, 1992). He stated that the agency instead would concentrate on the development of the Global Positioning System, known as GPS (see Feb 17, 1994). On Jun 8, FAA issued a request for proposals for an initial Wide Area Augmentation System (WAAS) for GPS. The initial WAAS would be a network of 24 ground stations and related communications systems that would enhance the integrity and availability of GPS signals (see entry for Aug 1, 1995). On Jul 16, Administrator Hinson and President Phil Boyer of the Aircraft Owners and Pilots Association landed at the Frederick, Md., airport using the first FAA-approved public "stand alone" GPS instrument approach. On Oct 17, the Administrator formally offered free use of GPS for 10 years to International Civil Aviation Organization member states, reconfirming a previous verbal offer (see entry for Apr 1, 1991). Other related events during 1994 included FAA’s Dec 8 announcement of approval of GPS as a primary means of navigation for oceanic/remote operations, subject to certain conditions.”

I thought I would try to give you a little perspective about the sales job the FAA is putting on for GPS and ADS-B. Once upon a time, they did the same for the Microwave Landing System (MLS) The great, touted advantage of MLS at the time was the ability of aircraft to fly “curved” approaches -- aircraft didn’t have to “line up” on the single beam a normal Instrument Landing System (ILS) provided. Just like GPS, controllers can envision this being useful but it wouldn’t increase airport capacity. I encourage you to read this link about MLS at Wikipedia.

In order to fully understand the debate, you will also need to understand a little about WAAS and LAAS. I’ll let others tell you about the benefits. I’ll stick to my usual role of pointing out the problems that the hype glosses over.


WAAS

Availability
”Availability is the probability that a navigation system meets the accuracy and integrity requirements. Before the advent of WAAS, GPS could be unavailable for up to a total time of 4 days per year.[citation needed] The WAAS specification mandates availability as 99.999% (five nines) throughout the service area, equivalent to a downtime of just over 5 minutes per year.”

Keep in mind that the availability of these systems is just fancy guess work. Controllers have running jokes about computers quitting. We’d be told no more than 5 minutes per year and then it would quit twice in three months, for 10-20 minutes each time. “Don’t worry guys. After we get through this one we won’t have another one for 20 years.” If you’ll read all the information about these systems, you’ll see that GPS is much easier to jam than the current system of VORs. You’ll also see that sunspot interference is a major concern -- which is one of the reasons that eLORAN is being looked at as a backup.
Speaking of backups...

LAAS

Drawbacks

”Another drawback of LAAS is the potential for a single point of failure. If the GPS system is interfered with it could result in serious problems if there is no backup method to land at the airport. Interference could be certain weather conditions, solar activity or malicious jamming of the GPS signal. It is possible that the FAA or local airports will keep existing ILS equipment to provide a backup in the event that the LAAS system should fail or if GPS is jammed. Requiring backup navigational equipment would seem to negate the justification of cost savings since redundant radios on the aircraft would cost users more than the current system. This also makes frequency management difficult because LAAS shares frequency space with its backup.

In order to mitigate these problems, the resulting national system will likely have LAAS capability at major airports, WAAS capability for the rest of North America with a limited amount of conventional navaids as a national backup.“

GPS, like MLS, sounds great coming out of the FAA’s PR machine. When you start looking at the details, it keeps getting stickier and costlier.

”Aircraft conducting WAAS approaches must possess certified GPS receivers, which are much more expensive than commercial units. In 2006, Garmin's least expensive receiver, the GNS 430W, had a suggested retail price of US$10,750 “

”The 2004 baseline estimates the final program cost to the US Federal government as over US$3.3 billion when delivered in 2013; more than 3.7 times the original budget and 12 years behind schedule “

It’s real easy to get wrapped up in all these details. The bottom line is the ability to safely put the maximum number of airplanes on the runway per hour and, of course, the bottom line -- money. GPS and ADS-B won’t increase runway usage. Not the ones that count. The ones at the major airports. We already have the technical capability to max out runway capacity. The calculations on cost aren’t nearly as cut and dried as the FAA would have you believe. Radars and ILSes are really expensive to build, maintain and replace. So are satellites and the ground stations needed to make them useful.

Don Brown
June 2, 2008