![]() Be sure the unit’s annunciators agree with which minima you expect to use. If not, your GPS still may be able to provide guidance for an LNAV or LNAV/VNAV procedure. If your aircraft legally can fly an LPV procedure, including consideration of the navigation database’s status, you’re good to go. There aren’t that many choices on the market for approved boxes, and-by design-they all work basically the same way. Of course, if the panel you’re flying behind doesn’t include a GPS navigator installation approved for LPV approaches, the question is moot. Approach plates for both procedures are reproduced on this and the opposite page. ![]() By way of explanation, we’ll take close looks at two procedures serving the same strip of pavement, Runway 35 at the Asheville (N.C.) Regional Airport. But when ATC wants to know which approach you’re requesting, do you automatically choose the newfangled GPS procedure or do you go with the old standby, the ILS? Which is best? As with so many things in aviation, it depends. At the same time, there’s something rather simple and perhaps romantic about an ILS. Some pilots are convinced the steadier signal digital GPS provides-when compared to the waviness of the analog ILS localizer and glideslope components-makes WAAS-enhanced approaches a no-brainer, even when there’s an ILS serving the same runway. There are other similarities, of course, including how we fly them. In typical configuration, either one can take us down to 200 feet agl and a half-mile visibility. If you need proof, look no further than comparing the faithful instrument landing system (ILS) to its WAAS GPS-based equivalent, the LPV (localizer performance with vertical guidance) approach. and similar technologies deployed in other countries, GPS is more accurate, more reliable and more repeatable than what came before. Thanks to the wide area augmentation system (WAAS) in the U.S. ![]() In less than 25 years, the “miracle” of GPS has transformed how even the smallest and least expensive aircraft navigates.
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