Written question (Use of GPS for DME or ADF at an alternate)
Asked by: Lemontree 7212 views Instrument Rating
Q. GPS systems certified for IFR operations can not be used as an substitute for ADF and DME receivers
A) to determine aircraft position or a DME fix a alititude above 24,000 feet
B) to fly a DME arc
C) in selection of an alternate that requires use of ADF or DME
The correct answer is C, and the explanation for the answer is: "Because GPS is not authorized as a substitute means of navigation guidance when conducting a conventional approach at an alternate airport, if the approach procedure requires either DME or ADF, the aircraft must be equipped with the appropriate DME or ADF avionics in order to use the approach as an alternate."
I'm not persuaded by this explanation, because according to the section C in AIM 1-2-3 and NOTE 1 right below it, suitable RNAV (which includes TSO-C129/-C145/-146 GPS) can be used to "determine aircraft position relative to, or distance from a VOR, TACAN, NDB, DME fix," and that "applies even when a facility is identified as required on a procedure (for example, "Note ADF Required")."
What do you think? Does the fact that the approach is an alternative make difference to whether or not a suitable RNAV can be used to replace a DME or ADF?
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