Precision Approach Capability Without Ground Installations

The Federal Aviation Agency has been preaching the gospel of GPS-based navigation for years, and the Holy Grail of satellite navigation has been a precision approach capability without an extensive investment in airport-specific on-ground equipment.

At the NBAA convention in Orlando, Florida, Rockwell Collins announced that the FAA had taken a major step forward, signing with the multinational communications/electronics company for the installation of WAAS/LPV equipment in the FAA's flight inspection aircraft.

What, pray tell, is WAAS/LPV?

WAAS is the Wide Area Augmentation System. Wide Area Reference Stations over the entire nation monitor the signals from GPS satellites. They then compare the data sent from the sites to their own precisely known locations, and compose and send error-correction messages to Wide Area Master Stations, and then back to the satellites. The satellites then send error-corrected GPS messages out and GPS receivers -- in our example, GPS receivers in aircraft -- receive them.

WAAS also adds significant error and outage alerting to GPS protocols. If the GPS system is unusable due to system errors or other effects, or hazardously misleading information that would cause an error in the GPS position estimate has been issued, users are notified within six seconds.

LPV is Localizer Performance with Vertical Guidance. (Why such an awkward acronym? Well, the FAA chose the acronym first, but didn't define it until August 2005). It can't be called a "precision approach" because of FAA and ICAO rules that require a precision approach runway to have specific runway markings, lighting, taxiways, etc. Someone at FAA realized that it would be silly to deny hundreds -- maybe thousands -- of runway ends, an approach capability with vertical lighting.

About 270 LPV approaches exist now, with another 300 expected in the next twelve months. Approach ceiling minimums are generally 250', with visibility minimums of 3/4 or 1/2 mile (depending upon runway lighting and markings).

But ultimately, WAAS LPV is a significant, even revolutionary, capability. The denotation of the acronyms is less important that their deeper meaning: with WAAS LPV, the U.S. National Airspace System can "provide horizontal and vertical navigation for precision approach operations for all users at all locations," according to the FAA. "This includes precision landing approaches in all weather conditions at all locations throughout the NAS."

Or, as Rockwell Collins's vice president and general manager of Business and Regional Systems, Denny Helgeson, put it, "This functionality will allow operators a means to perform precision approaches in low visibility conditions, and also has the potential to help meet future Required Navigational Performance (RNP) requirements."

Rockwell Collins's Cedar Rapids facility will work with the FAA's Aviation Systems Standards office in Oklahoma City to add WAAS LPV functionality to the FAA's (AVN) fleet of Bombardier Challenger 604 flight inspection aircraft.

The process will create a Supplemental Type Certificate (STC) to Challenger 604s type certificate. The STC is expected to be completed within the next two years. Installing this capability in FAA aircraft is an important milestone in the process of bringing vertical-guidance on all-weather approaches to all classes of aircraft.

FMI: www.rockwellcollins.com, www.gps.faa.gov