I am putting in a Garmin 430. That will be my only nav equipment. When doing the monthly VOR check can I check the VOR against what the gps says is the bearing to the VOR just like you would do if you had two VOR heads.

Tim

I'm not a genius when it comes to IFR flying... But I don't think that is allowed.

No.

MTV

Check FAR 91-171. Tells you to do everything except the most obvious, like using the obs function on the Garmin. Think about it, the VOR only has to be accurate to within 4 degrees of a bona fide test signal or location, but can be 6 degrees off on a known landmark. 60 miles away from a station it can be 6 miles off and still be legal. Your iPhone or Garmin 430 is accurate to about 6 feet.

I don't know anyone that uses VOR anymore. They are being decommissioned as we speak all over North America.

Interesting question but I doubt it..

$12,000 for an ifr legal 750 plus cost of keeping a gps updated is why I like vor's. Checking my vor's doesn't cost much. Gps jammers are not confidence inspiring either. 29 gps notams today, some covering 430 mile radius. Having another nav system and knowing how to use it isn't all bad.

I do not have a VOR gauge in my plane. When I did my Private Check Ride, I was allowed to use the VOR on my Garmin 396

I never used the 430/530 but won't either model tune a VOR? If so then you do your check as normal, i.e. against a landmark, point on the airport, vs. another VOR etc.

I blatently copied this for those interested:
AIM 1-1-19 (d)(1)(b) specifies the following:

“Aircraft using GPS navigation equipment under IFR must be equipped with an approved and operational alternate means of navigation appropriate to the flight. Active monitoring of alternative navigation equipment is not required if the GPS receiver uses RAIM for integrity monitoring. Active monitoring of an alternate means of navigation is required when the RAIM capability of the GPS equipment is lost.”

To the FAA lawyers "approved and operational" means totally legal including any paperwork such as the 30 day check.

AIM 1-1-19(e)(2)(a) specifies the following:

“GPS en route IFR RNAV operations may be conducted in Alaska outside the operational service volume of ground-based navigation aids when a TSO-C145a or TSO-C146a GPS/WAAS system is installed and operating. Ground-based navigation equipment is not required to be installed and operating for en route IFR RNAV operations when using GPS WAAS navigation systems. All operators should ensure that an alternate means of navigation is available in the unlikely event the GPS WAAS navigation system becomes inoperative.”

and more:

The bottom line is, when operating under IFR with GPS equipment on board, if you are equipped with a GPS unit that does not have WAAS capability, you must have the VOR checks within the preceding 30 days, and the equipment check must be within the prescribed tolerances as per 14 CFR 91.171 prior to departing into the IFR environment. Even if you have GPS with WAAS, it is highly recommended that you have this check anyway. After all, when that solar flare disrupts all our satellites, you will be happy to know that you have a backup navigation system to rely on while flying in hard instrument meteorological conditions.

porterjet wrote:I never used the 430/530 but won't either model tune a VOR? If so then you do your check as normal, i.e. against a landmark, point on the airport, vs. another VOR etc.

I blatently copied this for those interested:
AIM 1-1-19 (d)(1)(b) specifies the following:

“Aircraft using GPS navigation equipment under IFR must be equipped with an approved and operational alternate means of navigation appropriate to the flight. Active monitoring of alternative navigation equipment is not required if the GPS receiver uses RAIM for integrity monitoring. Active monitoring of an alternate means of navigation is required when the RAIM capability of the GPS equipment is lost.”

To the FAA lawyers "approved and operational" means totally legal including any paperwork such as the 30 day check.

AIM 1-1-19(e)(2)(a) specifies the following:

“GPS en route IFR RNAV operations may be conducted in Alaska outside the operational service volume of ground-based navigation aids when a TSO-C145a or TSO-C146a GPS/WAAS system is installed and operating. Ground-based navigation equipment is not required to be installed and operating for en route IFR RNAV operations when using GPS WAAS navigation systems. All operators should ensure that an alternate means of navigation is available in the unlikely event the GPS WAAS navigation system becomes inoperative.”

and more:

The bottom line is, when operating under IFR with GPS equipment on board, if you are equipped with a GPS unit that does not have WAAS capability, you must have the VOR checks within the preceding 30 days, and the equipment check must be within the prescribed tolerances as per 14 CFR 91.171 prior to departing into the IFR environment. Even if you have GPS with WAAS, it is highly recommended that you have this check anyway. After all, when that solar flare disrupts all our satellites, you will be happy to know that you have a backup navigation system to rely on while flying in hard instrument meteorological conditions.

John,

Actually, there's been an update to that policy, which permits stand alone GPS nav under IFR, IF the GPS unit (s) are WAAS enabled.

MTV

It is interesting that there is a requirement for TSO 145a or TSO 146a (WAAS) equipment for standalone GPS nav at all. A non-precision terminal GPS certified under TSO C129a is still far more accurate than VOR nav.

What does WAAS get you that the simpler C129a equipment does not in terms of a VOR replacement? I can't figure it out.

The trouble is that once WAAS becomes unavailable (which is a LOT of the time in the Rockies down in the normally aspirated altitudes), the same integrity checking method is used as C129a units. Basically, the WAAS GPS is no more accurate than a C129a unit when WAAS is unavailable. They both revert to RAIM integrity checking. And vertical position error information is only available when WAAS is available anyways. Even with WAAS, I see no practical advantage to knowing my position to within 18 feet over knowing my position to within 40 feet for an enroute or non-precision terminal operation.

TL;DR:

A GPS check of the VOR doesn't count as a legal VOR check. But it is still very likely to be far more accurate.

WAAS GPS units are often no better than non-WAAS IFR certified equipment in real conditions. Either type of GPS unit is orders of magnitude more accurate than VOR, even very close in to the VOR station.

WAAS is required for standalone RNAV GPS, even though it does not enhance the safety or utility of anyone while on an enroute (non terminal) segment over a non-WAAS IFR certified receiver.

It does cost a whole lot more, however, and that makes a lot of folks very happy.

lesuther wrote:The trouble is that once WAAS becomes unavailable (which is a LOT of the time in the Rockies down in the normally aspirated altitudes),

This is very interesting. I didn't realize the WAAS constellation was low enough to the horizon this would happen with any regularity. Most of my previous experience is with ground based nav when IFR. I recently bought a Garmin 400W for my plane project I hope to fly in a year. I will have VOR receivers in it, but assumed I would use GPS as primary for IFR ops, in the northwest.

Can you or anyone else speak to how often they loose WAAS integrity, under any flight rules?

Thanks, Jim

M3X wrote:I didn't realize the WAAS constellation was low enough to the horizon this would happen with any regularity. Most of my previous experience is with ground based nav when IFR.

I have a friend with a 430W, and it gets spotty any time he dips over the pass into a valley. He doesn't care, because areas with spotty WAAS where precision approaches are in effect have ground based WAAS broadcasts. I have a 300XL, a TSO C129a unit with basic RAIM. I have yet to see an integrity check flag come up.

Apparently, it isn't the geometry of the constellation,or how low the sats are, but instead the multipath signal rejection in some areas. Once the confidence interval drops for the WAAS specification accuracy, the flag goes up and it uses RAIM. This can be a function of receiver quality, but it can also be inherent to the technology. I don't know what the limits are, but I've read those NOTAMS for some rural airports which indicate GPS issues might be the result of some sort of WAAS availability simulation that predicts whether WAAS will be reliable or not.

On a trip from the front range to Meeker, we only "for sure" had WAAS a third of the trip, which averaged around 11k-12k.

A basic description is found here, although it is a bit outdated.

http://avionicswest.com/Articles/RAIM.html

Very interesting, thanks for the info and link! I will check it out.

Those C129a 300XL's sure look interesting to me; read everything I could on them. Super rugged I am told. My plan had been to get used 300XL as it does nearly everything I needed and was way more affordable.

When I called my avionics vendor to get on the list for the next used unit that came along they said, "ok, but we have a brand new, sealed in the box 400W (GPS only, no com or ground nav) for only a bit more". After nearly choking on my coffee I said send it! Sort of feel like I won the avionics lottery

I chose separate com and ground-nav radios to suit my architectural preferences, so the added value of the 430W was lost on me.

-Jim

What I have in my panel now is a GX55 gps that is not approved for approaches and to get it enroute certified I would have had to get a CDI installed. I have a KY97A com only radio and a transponder. I have no VOR that some of you have said will be obsolete in a matter of days. I want to be able to do a precision approach into North Bend.

The thought occurred to me to pull the radio and install an SL30 nav com and a glide slope indicator. But to do an ILS or LOC approach at North Bend you have to have a DME and ADF.

The expense of getting that all done and the fact that the screen on the GX55 was aging and the KY97A was losing some readout on the standby side pushed me to a decision.

A panel on a 1956 182 does not have a lot of extra room so the 430W just made a lot of sense do to it covering such a multitude of sins.

Tim

A GPS is a substitute for a DME with some caveats.

http://www.aopa.org/News-and-Video/All-News/1999/December/13/Use-of-GPS-in-lieu-of-DME-ADF

lesuther wrote:A GPS is a substitute for a DME with some caveats.

http://www.aopa.org/News-and-Video/All-News/1999/December/13/Use-of-GPS-in-lieu-of-DME-ADF

If they are IFR certified. The GPS I have is not unless I have a CDI installed and then if the screen goes out I have wasted a lot of money.

Tim

True. Bummer. But these things are crazy reliable...Ive burned through two gyros and rattled apart a blind encoder and an A/P head in the past 5 years. The Garmin is still ticking. If the display is a thing that goes bad on mine, perhaps I should be worried too.