GPS in lieu of DME?

Ophir

Well-Known Member
Can you use an approached certified GPS in lieu of DME? If so, what about if you have let the card lapse? Does this make your filing ability slide back to /A?
 

FL270

New Member
Yes. No. Yes.

An IFR approach certified GPS can be used in lieu of DME ... just make sure you've got the VOR vs. the airport dialed in to the box ... GSO and KGSO are not collocated, nor are BUF and KBUF ... just a couple off the top of my head. Of course, you already knew that.

Having a current database in the GPS is required in order for it to be used for IFR navigation. If the database is out of date, you're back to "reference only". Therefore, if your database is out of date and you have no DME, you're technically back to /U status ... since /A incorporates DME.

FL270
 

viper548

Well-Known Member
DONT PUT /A ON THE FLIGHTPLAN WITH GPS!!!! I did that once after we just got the Garmin 430's in the planes at the flight school. I didn't really know how to use the GPS that well, so I didn't want to put /G, so I figured I'd put /A because I could read the distance to the VOR's off the gps. I filed a DP out of Reno and it called for a left turn at 3 DME off of the localizer. I couldn't figure out how to load the DP in the gps. I was in a hurry to get home, so I just figured I'd eyeball the 3 miles since it was VFR. Approach caught me, I didn't quite make the 3 miles before I turned and they asked if my DME was working. I confessed that I had GPS and didn't know how to use it so I put /A on the flightplan. The controller then changed me to a /U. Huge learning experience.
 

Cosmo1999

Well-Known Member
You are only allowed to use GPS in lieu of DME if the database is updated and IFR current... There are a few restrictions on using GPS in lieu of DME, if you read AIM 1-1-21 it has all the info you could ever want about using GPS in lieu of DME... You are also allowed to use an IFR certified GPS as an overlay for approaches so you could load an approach and use all the info there for your distance info.. Once that little card has expired however no more in lieu of DME for you! They have to be updated something like every 28 days,well ours do anyway and its pretty darned expensive.
 

Ophir

Well-Known Member
Cool, thanks for answering that. I'm sorry I put the /A instead of the /U on the orginal post, it was late and I was going off memory.

So the deal is if you allow the card to lapse you have pretty much gone from a nice plane with great avionics to limiting yourself to using the old anolog stuff. I've gotta bug these guys here to keep the damn cards updated.
 

FL270

New Member
Falcon is right about the "slant range" issue ... however I suspect, Ophir, that you're talking about using the GPS fairly low down and close in to the navaids, so any difference would be minimal. And, if you're talking a VOR approach with a GPS overlay, the data has been test-flown and approved in any case.

Whenever you get new equipment, especially something complicated like a 430, take a lot of time to learn your way around the thing before you fly with it, especially from a mountainous terrain airport like Reno. Plug in a power cart and play with it for hours if that's what it takes to learn it. Then, you can load the DP in the GPS and get a point for the turn based on lat/long that will be at least as accurate (if not more so) than the DME.

A GPS without a current database is a bit like all that runway behind you ...

FL270
 

mtsu_av8er

Well-Known Member
[ QUOTE ]
so I figured I'd put /A because I could read the distance to the VOR's off the gps. I filed a DP out of Reno and it called for a left turn at 3 DME off of the localizer. I couldn't figure out how to load the DP in the gps.

[/ QUOTE ]

Common mistake, easy solution. Simply put the 4-letter identifier for the localizer into the GPS (I-DIE, I-GHY, etc) and you'll get the actual distance from the localizer.

DE tried to trick me up on the CFI-I checkride.....HA-HA...I got him!!
 

ananoman

New Member
One thing to watch out for when using the GPS in lieu of DME and ADF is choosing an alternate when IFR.

The approaches at your alternate cannot rely on GPS. So, if you plan on filing an airport as an alternate, and see that it has an ILS, you might think "great the weather is forecast to be 700 overcast, I am good to go". Make sure the ILS does not have a little note 'ADF or DME required', if it does, you may need to use a non-precision approach with higher alternate minimums, or choose a different airport.
 

SUSPilot

Well-Known Member
Ananoman
you are not exactly correct, you only have to choose an alternate that has an approach that does not require gps if the destination airport only has approaches that will require a gps for your airplane. So as by your example, In an airplane that is using a GPS in lieu of DME of NDB information, If the destination airport has for instance an ILS or a VOR approach that does not require DME or an ADF, then you can file as an alternate an airport that you will be required to use a GPS for an approach, whether that be a GPS approach or an approach requiring DME or an ADF. The reason for that alternate rule is so if there is a RAIM problem, you will be able to fly an approach to put the airplane on the ground without the GPS, but if your destination airport does not require a GPS then your alternate can. So basically one of your filed destination airports primary or alternate must have an approach that does not require a GPS, that does not mean you cannot fly an approach that requires a GPS at both of those airports, it just means that one of them must have an approach that doen't require a GPS.
 

ananoman

New Member
[ QUOTE ]
Ananoman
you are not exactly correct, you only have to choose an alternate that has an approach that does not require gps if the destination airport only has approaches that will require a gps for your airplane. So as by your example, In an airplane that is using a GPS in lieu of DME of NDB information, If the destination airport has for instance an ILS or a VOR approach that does not require DME or an ADF, then you can file as an alternate an airport that you will be required to use a GPS for an approach, whether that be a GPS approach or an approach requiring DME or an ADF. The reason for that alternate rule is so if there is a RAIM problem, you will be able to fly an approach to put the airplane on the ground without the GPS, but if your destination airport does not require a GPS then your alternate can. So basically one of your filed destination airports primary or alternate must have an approach that does not require a GPS, that does not mean you cannot fly an approach that requires a GPS at both of those airports, it just means that one of them must have an approach that doen't require a GPS.

[/ QUOTE ]

Your position is not supported by the AIM. AIM 1-1-20 list the requirements for GPS IFR operations. It also spells out the requirements to use GPS in lieu of ADF and DME. Nowhere does it say that you only have to have an alternate that does not rely on GPS if the approaches at your destination require the use of GPS. It does however state that: "A non-GPS approach procedure must exist at the alternate airport when one is required. If the non-GPS approaches on which the pilot must rely require DME or ADF, the aircraft must be equipped with DME or ADF avionics as appropriate." As far as I know, there are no exceptions to this rule. I also do not know of any airports that have only stand alone GPS approaches that are approved for use as an alternate.

Usually this is not an issue. If you need an alternate you can usually find one that has ILS or VOR approaches that do not require ADF or DME. However, if you are flying in bad weather and need a precision alternate, it can be problematic when the closest ILS list "ADF or DME required".
 

sixpack

New Member
Slant Range:
Difference between lateral and slant range on an ILS (assuming 3 degree glideslope) is less than 0.1 percent. On a non-precision, you could be off by as much as your AGL altitude.

Garmin 430.
Somebody mentioned powering up the airplane to playing with the GPS. If you have a Garmin 430, you can download a simulator for your computer (PC only) at www.garmin.com
 

xdashdriver

Well-Known Member
Firstly, the GPS must be used in accordance with the AFM supplement. The AFM supplement contains a Limitations section which lists the restrictions on the use of the GPS. Regardless of what the AIM says, the AFM supplement takes precedence in all cases. Best thing to do before using any GPS equipment is to read the supplement to find out what it's all about.

Secondly, when an approriately approved GPS is being used for IFR En Route and Terminal operations (not including the use of the GPS in lieu of ADF or DME equipment), the database may be used if expired, but only if the data can be verified as accurate (i.e. current maps and charts carried on board). A current database is required for any use in lieu of ADF/DME navaids, and for IFR approaches.

Thirdly, bear in mind that despite the approval to use GPS for IFR operations, the AIM also states that you need to have all of the avionics necessary to receive all of the ground-based facilities appropriate to your route of flight (including alternate) installed and operational. (Ground based facilities must also be operational)

Ray
 

250blue

New Member
You are correct Ananoman, no matter what your destination airport, if an alternate is required then that alternate must have an approach that does not rely on GPS.


[/ QUOTE ]Usually this is not an issue. If you need an alternate you can usually find one that has ILS or VOR approaches that do not require ADF or DME. However, if you are flying in bad weather and need a precision alternate, it can be problematic when the closest ILS list "ADF or DME required".

[/ QUOTE ]
A good example of this would be Tucson. Where I fly we cannot use it as an alternate because our planes do not have DME or ADF (Just GPS/VOR's) and all of their approaches depend on these.
 
Top