RAIM for non-GPS approaches

[trickeriche]

The following question was posed by a fellow CFI this morning and while I don't think any clear answer exists, I would like to hear some opinions.

"Does one need to verify RAIM when executing a non-GPS approach, but utilizing GPS for DME info?"

A scenario being a VOR/DME approach with a non-WAAS GPS providing DME information. The procedure does not have a GPS overlay. GPS database is current.

My thinking was that you would not need RAIM since you are only concerned with a point and three satellites would provide that to a reasonably accurate number. I have already been provided an argument staying that you would need RAIM. An additional scenario is loosing RAIM after the FAF. For a GPS approach, the unit should not flag for 5 mins after the loss of RAIM. If you're flying a non-GPS approach and lose RAIM after the FAF in the previous scenario, would the unit flag immediately or also wait the 5 mins? (This might be a manufacturer question.)

I could continue with more scenarios based on the original, but would like to see what the consensus is.

 

[Crockrocket94]

Err, I would guess since there is no overlay and that the Approach is a VOR/DME you would need to get your DME from the VOR. You can use your GPS as a reference or backup but the primary NAV is the VOR.

I would say "No" in regards to the RAIM because you are not flying a GPS based approach.

Dont quote me on it

Here is a discussion on GPS and DME.

Might be something of Value in there, but I dont think it directly answers your question.

http://forums.jetcareers.com/cfi-corner/114764-gps-lieu-dme-2.html

 

[Pilotforhire587]

I know its not an excuse but it has been quite a while since the ink dried on my instrument rating, that being said correct me if I am wrong.

I am pretty sure that if RAIM is unavailable you can't use GPS as your primary source of navigation en route while on an IFR flight plan in the first place. Even when you do have RAIM you must be able to back your navigation up with a ground based system such as VOR's or ADF's.


I would also agree with what was previously stated. If one is shooting a non gps approach one should use dme from the vor not the GPS

 

[Stone Cold]

Guys, read through the thread Crockrocket quoted. You can use GPS in lieu of DME for DME read out.

OP, I have never seen in writing anything saying you must verify RAIM for use in lieu of DME, but I think it would be smart to do. Maybe tgrayson or Midlife will vist this thread and provide some more insight!!

Err, I would guess since there is no overlay and that the Approach is a VOR/DME you would need to get your DME from the VOR. You can use your GPS as a reference or backup but the primary NAV is the VOR.

I would say "No" in regards to the RAIM because you are not flying a GPS based approach.

Dont quote me on it

Here is a discussion on GPS and DME.

Might be something of Value in there, but I dont think it directly answers your question.

http://forums.jetcareers.com/cfi-corner/114764-gps-lieu-dme-2.html

I know its not an excuse but it has been quite a while since the ink dried on my instrument rating, that being said correct me if I am wrong.

I am pretty sure that if RAIM is unavailable you can't use GPS as your primary source of navigation en route while on an IFR flight plan in the first place. Even when you do have RAIM you must be able to back your navigation up with a ground based system such as VOR's or ADF's.


I would also agree with what was previously stated. If one is shooting a non gps approach one should use dme from the vor not the GPS