If planning a flight with a WAAS receiver to both the destination and alternate, if the alternate airport has an ILS requiring GPS, do precision or non-precision standard alternate minimums apply?
Posted by Fabulous-Golf7949@reddit | flying | View on Reddit | 18 comments
The destination has an LPV approach and the alternate airport chosen has an ILS approach and I have chosen it as the ILS will likely be in use at the ETA due to forecast winds.
If the alternate airport has this ILS approach requiring GPS, do I use 600-2 (since it is an ILS approach) or 800-2 (since it requires GPS and, as we know, when planning an alternate with a WAAS receiver the planning must be based on LNAV/Circling lines of minima, i.e. 800-2 in this case).
Wondering if the AIM or any other publication offers an interpretation here. If the alternate approach is precision but requires GPS (even if GPS is substituting for DME/NDB), what alternate minimums should be used for planning?
TheGacAttack@reddit
What approach is this?
49Flyer@reddit
Quite a few now exist as NAVAIDs have been decommissioned and the feeder routes that were based on them no longer exist. In these cases GPS is required to identify IAFs and navigate to the localizer, but not for final approach guidance.
changgerz@reddit
just curious if you have examples? why could you not just use radar vectors? missed approach requires gps too?
49Flyer@reddit
Radar vectors don't exist everywhere, such as here: ILS Y 19R PABE
TheGacAttack@reddit
I just haven't ever seen an approach plate (or don't remember seeing one) for an ILS that states "GPS Required" on it. I understand using GPS as a method for identifying and navigating navaids.
kmac6821@reddit
It won’t. The NavSpec would be RNAV1. (GPS is not a navigation specification, but in the US it is required to meet the RNP APCH NavSpec, which the ILS would not have. That would just be RNAV1 and has no bearing on alternate minima.)
Fabulous-Golf7949@reddit (OP)
They’re not uncommon now, at least out east with the shift to the MON. Some of these ILS approaches require GPS to identify a fix on the plate.
TheGacAttack@reddit
Ok, but in your situation, which airport is your chosen alternate?
Fabulous-Golf7949@reddit (OP)
Take any ILS approach, even one requiring DME for which an aircraft is only equipped with an IFR approved GPS to be used in lieu of the DME. GPS here would be required to fly the approach. Take the ILS RWY 6 at KMHT, for example.
TheGacAttack@reddit
It's _not_ "GPS required" it's "DME required." How you satisfy that DME requirement doesn't matter. It's an ILS approach, which is a precision approach, which is 600-2 as the alternate.
TheGacAttack@reddit
600-2.
kmac6821@reddit
You’re incorrectly equivocating an RNAV approach (which for alternate planning is a non-precision and thus would require circling mins) with an approach that requires GPS. The two are not the same. In this example, all that matters for the alternate is that it is a precision approach.
49Flyer@reddit
The ILS in this case is still a precision approach; the note "GPS required" is only for navigation in the initial and intermediate segments and/or the missed approach. It's no different than an ILS or VOR approach that says "ADF required" because certain fixes can only be identified with an NDB.
cazzipropri@reddit
600-2
Fabulous-Golf7949@reddit (OP)
Makes sense.
YaaniMani@reddit
My take would be 600-2 since it’s an ILS approach which is a precision approach by definition.
OriginalJayVee@reddit
I am also curious!
rFlyingTower@reddit
This is a copy of the original post body for posterity:
The destination has an LPV approach and the alternate airport chosen has an ILS approach and I have chosen it as the ILS will likely be in use at the ETA due to forecast winds.
If the alternate airport has this ILS approach requiring GPS, do I use 600-2 (since it is an ILS approach) or 800-2 (since it requires GPS and, as we know, when planning an alternate with a WAAS receiver the planning must be based on LNAV/Circling lines of minima, i.e. 800-2 in this case).
Wondering if the AIM or any other publication offers an interpretation here. If the alternate approach is precision but requires GPS (even if GPS is substituting for DME/NDB), what alternate minimums should be used for planning?
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