What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

GPS Only IFR - Alternate Airports

CharlieWaffles

Well Known Member
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.
 
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.
 
Last edited:
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.
 
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.
 
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?
 
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.
 
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.
 
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.
 
Last edited:
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.
 
Thanks, that is the same info I have. Basically you can do LPV at one airport, but the other you can only do lateral navigation (LNAV/VNAV).

olicy Clarification for WAAS Users

The current alternate airport planning policy explicitly prohibits TSO-C145() and TSO-C146() equipped users (WAAS users) from planning to use WAAS vertical guidance at their alternate airport.

There are some WAAS integrations that use baro-VNAV for vertical guidance. WAAS users should consult their flight manuals for this information. This policy clarification allows properly trained and approved, as required, WAAS users equipped with and using approved baro-VNAV equipment to plan for applicable alternate airport weather minimums using:

1. LNAV/VNAV DA at an alternate airport.

2. RNP 0.3 DA on an RNAV (RNP) IAP at the alternate airport if specifically authorized.

The FAA based this policy clarification on the facts that GPS-based lateral guidance is the same for LNAV, LNAV/VNAV and RNP 0.3 DA and approved barometric vertical navigation equipment does not rely on GPS information. Therefore, a loss of GPS vertical would not affect these WAAS users navigating vertically with baro-VNAV.
 
Don't confuse "you can do.." with "you must plan for..." -- you *still* CAN do LPV at your alternate... but must plan for LNAV only.

Keep in mind there's an operational limitation anyways that has nothing to do with what the rules say.. and that's that at most places the only weather forecast available is area forecast that is simply not granular enough to differentiate anyways.. so in reality whether your alternate has LPV or just LNAV would make no difference for planning purposes... it'll still have to be VFR to choose most of these smaller airports as alternates.
 
If you are really going to fly IFR you need to install a NAV Antenna as a backup to the GPS. Before Garmin finally replaced my GTN650 I had multiple GPS failures. Including a GPS failure on approach into Rapid City between two large thunderstorms and a fire TFR on the way to Oshkosh. I have also experienced complete GPS outages (all 5 GPS units in the RV-10) in the Reno area on more than one trip.

You have already paid for the radio and it should not take more than a few hours to install the antenna. I have a separate Archer Antenna in each wing tip of the RV-10, one to the GTN650 and one to my backup Nav radio.

Rob Hickman
Advanced Flight Systems Inc.
N402RH RV-10
 
+1 with Rob. At this point the only hard thing about putting in an Archer antenna will be pulling the coax.

And, to repeat what others said: you may fly an LPV approach at the alternate airport, but you need to plan on an LNAV approach (the forecast has to call for 800' ceilings or better (standard, non precision), not 600' or better.)
 
Just remember not all GPS approaches are equal, you have Lnav, Lnav/Vnav and LPV. They all have different mins and LPV is the only one that can be classified as a precision approach.

My rule of thumb is alternates must always have a ground based approach. Even if it is non-precision. I trust the GPS about as far as I can throw it and well I cant throw it very far with out throwing the plane too.

The GTN 750 in my experiences has been rock solid and its a great tool to have. However, I would not use it for sole IFR flight (plus those other NavAid help you stay current).
 
Just remember not all GPS approaches are equal, you have Lnav, Lnav/Vnav and LPV. They all have different mins and LPV is the only one that can be classified as a precision approach.

My rule of thumb is alternates must always have a ground based approach. Even if it is non-precision. I trust the GPS about as far as I can throw it and well I cant throw it very far with out throwing the plane too.

The GTN 750 in my experiences has been rock solid and its a great tool to have. However, I would not use it for sole IFR flight (plus those other NavAid help you stay current).

I'm not a true fan.............of those other NavAids. A prime interest in life for me, was why all of those airplanes crashed into rising terrain, for all of those years. I do live in mountain country, which is heavily "dotted" with CFIT accident sites. GPS "is" making the difference, and it's finally being noted as doing so. BTW--- a friend of mine, who flies for a major airline, keeps track of GPS failure (their Boeing uses GPS as the main nav source)...............for my benefit. We're up to 14 years now.
 
If you are really going to fly IFR you need to install a NAV Antenna as a backup to the GPS. Before Garmin finally replaced my GTN650 I had multiple GPS failures. Including a GPS failure on approach into Rapid City between two large thunderstorms and a fire TFR on the way to Oshkosh. I have also experienced complete GPS outages (all 5 GPS units in the RV-10) in the Reno area on more than one trip.

You have already paid for the radio and it should not take more than a few hours to install the antenna. I have a separate Archer Antenna in each wing tip of the RV-10, one to the GTN650 and one to my backup Nav radio.

Rob Hickman
Advanced Flight Systems Inc.
N402RH RV-10

Any notams for the Reno area? Testing, time????
I confess...........I'm not much for radio nav. Today, I'm going to install a new A/C unit. Just below the area, where a United DC-8 cargo jet slammed into the mountain, in 1977. Much to do with "radio". Even a cheap handheld model...........of todays GPS units, would have prevented that one. Every day, I look at a mountain peak, where a "airliner" disappeared for nearly six months, back in '36. Amelia Earhart even flew up to look for it.
 
Last edited:
Those Navy boys at Fallon Like to have fun with GPS signals.
One thing to keep in mind is should we end up in a major conflict with the new Soviet Union you might have a extended period of higher GPS mins mandated by a blanket notam.
 
Back
Top