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Back in the database: when WAAS upgrades have center stage, here's a chart update from the wings that throws a bone to fliers of LNAV-only GPS.

IFR Staff

Back in 2005, we noted that your IFR-certified GPS might not be allowed to fly a perfectly good GPS approach because the published procedure wasn't in the database ("Not in the Database," October 2005 IFR). The situation popped up where there were two RNAV approaches to the same runway. Under the new approach nomenclature, one would be the RNAV (GPS) Y approach and one would be the RNAV (GPS) Z.

The approach plate existed, but if you were a Jeppesen user, you'd see the words "Procedure Not in Database" prominently displayed on the plate. NACO users would get the surprise later when they tried to select the correct RNAV approach and discovered that only the Z approach was available.

This happened because older flight management systems couldn't accept multiple approaches of the same type to the same runway. Jeppesen's interum solution was to only put one approach in the database delivered to manufacturers.

The problem, though, is the approach choosen was whatever was closest to the end of the alphabet. So if there was Y and Z approach, the Z was published. This was usually the LPV or LNAV/VNAV version. These approaches have different TERPS criteria and issues with stepdown fixes than a plain LNAV approach, however, and the Z approach might have higher LNAV-only minima than the Y approach LNAV minima.

Even when the Z and Y approaches used exactly the same ground track, GPS users couldn't legally fly to the Y minima because they could only load the Z approach. The irony here is that most GA GPS units could easily accommodate both approaches in their databases.

Starting in February of 2006, the option for multiple approaches was opened to manufacturers and current databases for Garmin 400-, 500-, and 480-series GPS units are starting to offer both Y and Z approaches.

Exactly where and when is still in flux, but keep an eye out for some extra approaches popping up in your database--and for some extra verbiage disappearing from some charts.

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Title Annotation:APPROACH CLINIC; Wide Area Augmentation System; Lateral navigation; global positioning system
Publication:IFR
Article Type:Brief article
Geographic Code:1USA
Date:May 1, 2007
Words:336
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