This post came from Jason as an e-mail and has been posted in the forums for the benefit of other students.

Im studying your Instrument Rating study guide and if you could, please provide clarification on on the use of GPS and alternates
it would be greatly appreciated.

If im reading correctly, an aerodrome with only an RNAV or GPS arrival procedure must be treated as having no approach if using
a gps certified to TSO-C129[a] and an alternate for the sake of planning must be used
However if the GPS is certified to TSO 145/146[a] with FDE then the approach can be made. Would this be correct and

Consider an aeroplane with an ADF and GPS planning a charter flight to an aerodrome with one NDB approach along with a RNAV {gnss} and GPS arrival
procedure. This flight would require an alternate since you cannot use a GPS procedure to satisfy the alternate requirements.

is the above for VH-OZY as it only has a TSO C129[a], and if an aircraft was fitted with a TSO 145/146[a] than the failure of the NDB you wouldn’t need
an alternate because you can still carry out a RNAV/GPS approach

You have got it right. If a GPS is TSO-129 you simply ignore it when it comes to satisfying alternate requirements. However if you have a TSO-145/6 GPS, you can treat it as being equal to any 'conventional' aid when it comes to alternate planning. The quote you have given in italics should have mentioned that but was written before the 145/6 equipment became available. Thanks for mentioning it, I'll find that statement and change the wording.