GPS Only IFR - Alternate Airports

CharlieWaffles · #1 06-09-2014, 06:41 PM

What is the current set of regulations around IFR only GPS, specific to alternate airports. I know that GPS only IFR is allowed, but I have seen some articles that said the alternate could not also be GPS approach (either/or only). But I also saw some articles that said some TSOs allowed both approaches to be GPS only. In my case, I have a GTN750.

BobTurner · #2 06-09-2014, 07:12 PM

The original, non-WAAS GPS boxes approved under TSO 129 were to be used only as "supplemental" navigation. Other nav boxes (e.g., VOR) had to be on board and useable over the route flown. If an alternate airport was required, then the aircraft had to be capable of flying a non-GPS approach at that alternate (and that approach had to have appropriate alternate minimums).

No new boxes can be certified under TSO 129.

Newer boxes, such as the 400W series and the 650 series, are certified under TSO 145 (or is it 146?). They may be used as "sole source" of navigation, and all the above restrictions do not apply.

Whether or not the risk-benefit ratio for this type of operation is suitable is left to the PIC.

rleffler · #3 06-09-2014, 07:15 PM

Quote:

Originally Posted by CharlieWaffles

What is the current set of regulations around IFR only GPS, specific to alternate airports. I know that GPS only IFR is allowed, but I have seen some articles that said the alternate could not also be GPS approach (either/or only). But I also saw some articles that said some TSOs allowed both approaches to be GPS only. In my case, I have a GTN750.

I don't have the regs handy, but the GTN series can use a GPS as an alternate, whereas the older GNS series can't.

I'm sure that somebody will follow up with the details.

BobTurner · #4 06-09-2014, 07:29 PM

Quote:

Originally Posted by rleffler

I don't have the regs handy, but the GTN series can use a GPS as an alternate, whereas the older GNS series can't.

I'm sure that somebody will follow up with the details.

By "older GNS" series you mean the non-WAAS boxes, that is correct.
The 400W series are TSO'd to 145 and can use an alternate with GPS only.

Note the rule with TSO 129 boxes is for flight planning (and fuel-carrying) only. You need to have enough fuel to make it to a suitable alternate with your 129 GPS inoperative; plus reserves. If it's working, you can still use it to shoot a gps approach at an alternate. You just have to have a backup, too.

Soju Hunter · #5 06-10-2014, 06:57 AM

Quote:

Originally Posted by CharlieWaffles

What is the current set of regulations around IFR only GPS, specific to alternate airports. I know that GPS only IFR is allowed, but I have seen some articles that said the alternate could not also be GPS approach (either/or only). But I also saw some articles that said some TSOs allowed both approaches to be GPS only. In my case, I have a GTN750.

Why ask the question when your box is equipped with radio NAV? Antenna not installed?

rleffler · #6 06-10-2014, 09:00 AM

Quote:

Originally Posted by Soju Hunter

Why ask the question when your box is equipped with radio NAV? Antenna not installed?

Typically the minimums are greater for the non-precision approaches, such as VOR, NDB, etc. If the alternate is a small airport, it may not have an ILS, making the GPS/RNAV the preferred approach.

CharlieWaffles · #7 06-10-2014, 10:13 AM

Quote:

Originally Posted by Soju Hunter

Why ask the question when your box is equipped with radio NAV? Antenna not installed?

Correct, I did not install a NAV antenna, cable, etc...

DGlaeser · #8 06-10-2014, 10:43 AM

Quote:

Originally Posted by CharlieWaffles

Correct, I did not install a NAV antenna, cable, etc...

As noted earlier, since you have a WAAS GPS, there is no requirement to have another nav system (i.e. VOR/LOC), for either the primary or alternate airport.

Without the VOR/LOC antenna installed, you are 'limited' to selecting only GPS approaches (your database will have all the non-GPS approaches as well of course). These days it is not much of a limitation, but something to verify at your intended destinations.

KatieB · #9 06-10-2014, 10:53 AM

Quote:

Originally Posted by CharlieWaffles

Correct, I did not install a NAV antenna, cable, etc...

GPS outages are rare, but they can happen. Since you already have VOR/LOC, why not stack the cards in your favor? The antenna install might be a pain but you might come to rely on it as your backup someday.

CharlieWaffles · #10 06-10-2014, 11:13 AM

Quote:

Originally Posted by DGlaeser

As noted earlier, since you have a WAAS GPS, there is no requirement to have another nav system (i.e. VOR/LOC), for either the primary or alternate airport.

Without the VOR/LOC antenna installed, you are 'limited' to selecting only GPS approaches (your database will have all the non-GPS approaches as well of course). These days it is not much of a limitation, but something to verify at your intended destinations.

Any chance you know the specific FAR or publication from the FAA that confirms this? This is my understanding but I have to admit I cant find it in the FARs.