No DME

[Instrumental]

Hello,

My plane is an older 172 w/o DME and I've been looking for an excuse to install a GPS. If the GPS has a VOR database can I use it for arcs?

[Gimble]

Originally Posted by Instrumental

My plane is an older 172 w/o DME and I've been looking for an excuse to install a GPS. If the GPS has a VOR database can I use it for arcs?

I'll take a stab at this since nobody else has.

Obviously, for IFR flight, you must use certified equipment. This precludes all handheld GPS units and VFR in-dash GPS units.

With an IFR certified GPS, the answer is "usually" you can use the GPS as a substitute for DME. This article explains it better than I can:

A Flight Instructor's Journal: October 2007

As a side note, I currently have a DME in my plane, and am adding an IFR GPS ( Garmin 430 ). While I'm going to remove the ADF, I plan on leaving the DME just to allow flexibility for DME arcs.

[Instrumental]

Thanks!

As I've moved further into IFR training I've become aware that the GPS, regardless of its rated capacity (VFR vs. IFR) has to be backed up with a secondary system (according to the Jeppesen text). There's the argument that the RAIM equipped GPS doesn't require monitoring the secondary, but it doesn't seem to remove the requirement. Like you, the 430 is a tempting route, but unless I'm reading this all wrong I can't just stuff a 430 in the dash and call it "good".

[Gimble]

From the AIM ( http://www.faa.gov/air_traffic/publi...1/aim0101.html ), which is "non-regulatory":

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.

Also, from the FAA ( GNSS Library ):

Q. Can my aircraft be equipped only with GPS for navigation and be legal for flying in IMC?

A. The FAA has authorized GPS as the primary means of navigation in certain areas (oceanic and remote). The FAA requires that the aircraft have the appropriate equipment necessary for the route of flight. Furthermore, a GPS approach cannot be used for the alternate if it is also used for the destination when using TSO-C129 equipment. Therefore, it may be legal to fly a GPS-only equipped aircraft in IMC, but the circumstances are quite rigorous. In Alaska , IFR-approved and installed WAAS avionics are legal as the only navigation equipment on board if the route and destination are identified for GPS/WAAS

.It does look to me like the DME would be required, even if not used (at least today). Still, I've seen at least one CFII online who recommends taking a checkride with just a 430 in the plane, to reduce the number of systems the applicant would be tested on during the exam.

[Gimble]

And yet, to argue the other position, this note at AOPA seems to indicate that in 1998 there was a policy change specifically to allow the use of GPS to replace DME/ADF -- meaning complete replacement.

AOPA, working together with the FAA Flight Standards Division, has reached agreement on FAA policy changes that permit IFR-certified GPS receivers to be used in lieu of DME and ADF for most IFR operations (see "Limitations"). This policy fundamentally permits DME and ADF avionics to be removed with little compromise in operational capability.

(Emphasis mine)

Source: AOPA Online: Air Traffic Services Brief -- Use of GPS in lieu of DME/ADF