Upgrading to WAAS: only a few options exist; a WAAS buy-in adds real mission capability and workload reduction. but walk-away costs vary wildly with glass cockpits taking the biggest hit.(AIRCRAFT UPGRADES)(Wide Area Augmentation System)(Report)

In February 1996, the FAA's Technical Standard Order (TSO) C129 put IFR GPS navigation on the map. It was a complex installation with equipment that was quirky to program, but early adopters gained GPS-direct flight plans and GPS approaches--even though GPS was "supplementary navigation."

Today's IFR GPS installations are all about the augmented WAAS signal that's worthy of sole-means navigation. They're still a source of confusion and expense, but WAAS installations yield impressive automation and capability. Before you decide if WAAS is for you, you need to understand some behind-the-scenes facts and why you could be disadvantaged without WAAS GPS in your aircraft.

IT'S ABOUT SIGNAL QUALITY

WAAS and precision-GPS equipment, procedures and regulations are covered in TSO C146a. The technical and operational benefits of a WAAS interface are many, and the new WAAS GPS engines, processors and software are reliable and highly accurate. WAAS not only enhances GPS accuracy but also corrects the errors in GPS signals caused by ionospheric effects.

WAAS provides less than 1.5-meter horizontal accuracy and 3-meter vertical accuracy. Class 3 WAAS sensor capability means no other navigational gear is required. If this sounds like putting all the eggs in a single basket, it is. These owners are relying completely on quality installations.

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Operational WAAS also doesn't require user to check RAIM--receiver autonomous integrity monitoring--which was an early GPS system for alerting a pilot if the GPS signal quality had gotten too poor for navigational use. All WAAS GPSs use Fault Detection and Exclusion (FDE), which detects satellite failure and ignores the failed satellites. This ultimately affects the signal integrity and performance of the unit, and may mean the box will only offer you an LNAV approach with no vertical guidance rather than the LPV you were hoping for. That's because the boxes are smart enough to "downgrade" a WAAS GPS approach back to a basic non-precision GPS approach 60 seconds prior to reaching the FAR This possibility is why the FAA is so particular of the placement of mode annunciation that alerts the pilot to GPS messages.

If a WAAS outage is predicted and NOTAM'd, then you should …