TSO Requirements for GPS Annunciator Panels

[Harold Rutila]

I'm trying to find the TSO for an Avidyne IFD installation that would mandate a GPS annunciator panel be installed if the CDI source selector is more than 13.8 inches from the main attitude indicator.

Yes, this is already a requirement in the Avidyne installation guide, but apparently one of their reps is insisting this is no longer a requirement. I can't find any source documents that would suggest it is no longer required.

 

[flyingron]

The rule I believe is that the source INDICATOR (i.e., whether the thing is tracking VOR or GPS) has to be within a certain number of inches (11?) of the center of the primary pilot instruments (six pack). I assume this is buried in the TSO-C146 varients. Note that reading TSOs is often a futile effort as they just reference various RTCA docs which are not openly accessible.

Note that no matter what the guy said, if the IFD installation instructions say you need an annunciator, even if the TSO changes that doesn't negate that. Avidyne needs to update their documentation if that isn't the case.

My GPS (a GNS480) is too far to the right as well. All I have is a pair of "press to test" lights reading NAV and GPS that are installed adjacent to my HSI. Some of the "designed for IFR GPS" nav heads have the annunciator lights built in.

 

[SbestCFII]

When I had my Cherokee with a KLN94, the annunciator and CDI selector was installed on the secondary stack (to the right of the main stack) and was outside the 13.X inches from the center of the primary instrument panel required by the TSO (the installer put it there to short-cut). Though the install technically wasn't legal, it worked just fine for years and I didn't know better. With a panel renovation in 2006 by another shop, this was corrected. Though the KLN 94 had annunciations built into the display, but they were on the far right side of the unit and outside of the 13.X inch limit, so it required the remote annunciator closer to the pilot. In my current plane, my 430W has it's annunciations and CDI selector on the left side of the GPS display and on the primary (left-sided) radio stack, falling within the 13.X inch limits.

The source indicator (GPS/NAV) is the main thing for newer WAAS GPS. With the older units you needed annunciation of the mode, approach ARM and then Active (ACTV) where the GPS would go into the ACTV mode 2-3 NM outside the FAF to let you know you had adequate RAIM accuracy to descend to the MDA during an approach. If the ACTV mode didn't annunciate, then you couldn't descend.