gismo
Touchdown! Greaser!
Ron, you (or someone using your name) wrote to IFR magazine saying that "You are not permitted to use a GSP as a DME substitute to fly a DME arc on a VOR/DME approach unless there's a GPS overlay for that approach and you have an approach GPS..." The AIM seems to disagree (see excerpts below). While there is the disclaimer:
AIM said:NOTE-
This approval does not alter the conditions and requirements for use of GPS to fly existing nonprecision instrument approach procedures as defined in the GPS approach overlay program.
...it doesn't seem consistent with the rest of what the AIM has to say on the subject to say you can't fly a DME arc with GPS.
AIM said:1-1-19.Global Positioning System (GPS)
AIM said:f. Use of GPS in lieu of ADF and DME(a) Operations allowed:1. Subject to the restrictions below, operators in the U.S. NAS are authorized to use GPS equipment certified for IFR operations in place of ADF and/or DME equipment for en route and terminal operations. For some operations there is no requirement for the aircraft to be equipped with an ADF or DME receiver, see subparagraphs f6(g) and (h) below. The ground-based NDB or DME facility may be temporarily out of service during these operations. Charting will not change to support these operations.
(2) Flying a DME arc.
AIM said:(c) Guidance. The following provides general guidance which is not specific to any particular aircraft GPS system. For specific system guidance refer to the AFM, AFM supplement, pilot's guide, or contact the manufacturer of your system.
AIM said:
(2) To fly a DME arc: [a] Verify aircraft GPS system integrity monitoring is functioning properly and indicates satisfactory integrity.You must select, from the airborne database, the facility providing the DME arc as the active GPS WP.
NOTE-
The only acceptable facility is the DME facility on which the arc is based. If this facility is not in your airborne database, you are not authorized to perform this operation.[c] Maintain position on the arc by reference to the GPS distance in lieu of a DME readout.
Now I know this letter mentions the KMTN VOR/DME (or TACAN) 15 approach which is unusual in that the DME arc leads to the MAP/runway rather than a VOR final approach course segment but certainly on an approach like the BWG VOR/DME 21 it must be legal to fly with a GPS (and VOR) and no DME. And I can't really see why you couldn't legally fly the MTN VOR/DME 15 with a GPS and VOR either, but I admit I'm not so sure about that.
http://download.aopa.org/iap/20051027/SE-1/bwg_vor_dme_rwy_21.pdf
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