GPS at Alternates

[TopperHarley]

Hey guys,

I've been hearing different things from different folks, so I would like some clarification.

If you want to take credit for a GPS Approach at an alternate, which mins apply?

1. The old "No IFR Approach" mins of 500 ft above a minimum IFR altitude, OR
2. 800-2/300-1 above lowest usable HAT... the mins for a non-precision approach?

I know it used to be #1, but some people have said it has since been changed to #2.

Also, if #1 does apply, what is considered "a minimum IFR altitude?" Is it the MSA/safe 100nm altitude/AMA, etc?? Can you just pick one of these?

Thanks in advance.

[Disco Stu]

Check the front of the current CAP GEN Chris,

GPS alternates have to meet the exact same criteria as regular alternates. 800 and 2 or 400 and 1 above lowest usable HAA/rec vis.

However your destination airport must have a traditional approach aid to take credit for a GPS approach at alternate.

[ahramin]

Like Disco Stu said, CAP GEN. Page 15. There are thousands of copies out there Chris, get yourself one and read it cover to cover. No offense, but while we are perfectly happy to clarify anything in there, if you want to be a good IFR pilot, you are going to need to look the simple ones up for yourself . When you ask here you are likely to get a bunch of answers, some better than others. You get a good range of information. But if you look it up yourself you will get a much bigger range of information as you try to find it, with far more of it correct, and a far more complete answer when you do.

And yes, in the bad old days you could not take credit for a GPS approach for alternate minima. Slowly but quasi-surely, TC is being pulled kicking and screaming into the 20th century.

Lastly, if you a 604 or part 7 operator you will need the ops spec before you can take credit for any GPS approaches.

[TopperHarley]

Thanks for the responses guys.

I actually did reference the CAP GEN, as well as the AIP (I still haven't received the AIM)- the problem is that my CAP GEN is outdated (Nov 2004), so I was confused as to the wording in the GEN.

This is an exert of the old version of the CAP GEN which confused me: "Operators or pilots can take credit for a GPS approach at an alternate, provided that the destination is served by traditional aids.... otherwise, when determining alternate aerodrom minima requirements, the operator or pilot shall only take credit for functionning traditional aids at that aerodrome. In this case, if the alternate aerodrome has GPS approaches only, the pilot shall use the minima for 'No IFR Approach Available."
I guess this has since been reworded in the new AIM, where it states you can use the non-precision approach mins of 800-2/300-1 above the lowest HAT (using the HAT for the L-NAV mins only).

The other issue which confuses me is dealt with in COM 3.16.12.1 in the AIM, where it states how pilots must check GPS Notams for RAIM availability and use "commercially available dispatch RAIM prediction software" to manually deselect any predicted satellite outages, assuming 2+ satellites are predicted to be out of service. I just don't understand how pilots go about doing this.

[pelmet]

Am I correct in saying....If the alternate has only a GPS approach then destination must have a traditional approach. Also, if the destination only has a GPS approach, then the alternate must have a traditional approach.

[Fork-Tailed Devil]

A pilot can take credit for a GPS approach at an alternate aerodrome when all of the following conditions are met:

-A useable approach at the destination is served by a functioning traditional aid

-The pilot or operator determines that approach-level RAIM will be available at the alternate aerodrome at the expected time of arrival using methods that take account of predicted satellite outages. If you do not have access to RAIM predict software the following method satisfies the requirements:

-Determine the ETA at the proposed alternate aerodrome following a missed approach at the destination.

-Check GPS NOTAMs (by querying NOTAMs for identifier KGPS) for a period of 60 min before and after the ETA. If not more than one satellite outage is predicted during that period, then conditions are satisfactory. If two or more simultaneous outages are anticipated during the ETA + or - 60 min period, then it is necessary to select a suitable alternate serviced by traditional navaids.

-For TSO C129/C129a avionics, periodically during the flight, and at least once before the midpoint of the flight to destination, the pilot uses the avionics to perform a RAIM prediction for the alternate aerodrome at the expected time of arrival. If an in-flight prediction indicates that approach-level RAIM will not be available at the alternate, the pilot should plan accordingly.

As long as you meet these requirements you can apply non-precision approach minima to your GPS alternate.

[pelmet]

Sounds to me like what you are saying is if you only have 1 GPS on board, like many private operators, you can't have a GPS only destination or alternate because if that unit fails, you can't do the approach. Is this a regulation written down somewhere.

[ahramin]

I deleted my previous post because it was confusing.

If the alternate has only a GPS approach then destination must have a traditional approach. Also, if the destination only has a GPS approach, then the alternate must have a traditional approach

You have it half right. To use GPS approach minima for calculating approach minima the destination must have a traditional approach regardless of whether the alternate has a traditional approach or not.

If the destination only has a GPS approach, then you cannot use a GPS approach for alternate minima, no matter what other approaches are available at the alternate.

As for only having one GPS unit,

(j) sufficient radio navigation equipment to permit the pilot, in the event of the failure at any stage of the flight of any item of that equipment, including any associated flight instrument display,

(i) to proceed to the destination aerodrome or proceed to another aerodrome that is suitable for landing, and

(ii) where the aircraft is operated in IMC, to complete an instrument approach and, if necessary, conduct a missed approach procedure.

So as long as the fuel and weather are good enough to get somewhere (anywhere) and do an approach with whatever you have left after the GPS failure you are good to go. In other words if you are using a GPS approach for an alternate and only have one GPS unit be damn sure you are going to be able to get to your destination and land there without your GPS or carry enough fuel to get where the weather is good.

The rules are pretty lax. I only use CAP GEN minima for figuring fuel and alternates on fair to good weather days. If there is any chance that you will not make it into your destination with or without an equipment failure, load up enough fuel to make it to a good alternate, not a CAP GEN acceptable one.

[bluesideup]

you also have to be "GPS certified" in order to use the GPS to do an GPS approach in the first place...

[TopperHarley]

A pilot can take credit for a GPS approach at an alternate aerodrome when all of the following conditions are met:
If you do not have access to RAIM predict software the following method satisfies the requirements:

-Check GPS NOTAMs (by querying NOTAMs for identifier KGPS) for a period of 60 min before and after the ETA. If not more than one satellite outage is predicted during that period, then conditions are satisfactory. If two or more simultaneous outages are anticipated during the ETA + or - 60 min period, then it is necessary to select a suitable alternate serviced by traditional navaids.

This is not consistent with what is written in the AIM (See COM 3.16.12, pg 86).

In addition to the requirements you listed, the lowest landing limits you can only use are the LNAV minima (i.e. no LNAV/VNAV or LPV). So, I guess this means the mins are 800-2, or 300-1 above the lowest HAT of the LNAV mins.

In the AIM, it seems to imply that you must always check GPS Notams (KNMH) prior to any flight where your alternate is served by only a GPS approach.

Furthermore, it states that if 2 or more satellites are predicted to be out of service, you must use commercially available dispatch RAIM software, acquire an almanac, and manually deselect those U/S satellites for the times decribed in the NOTAM. To me, this process sounds a little confusing, and I don't fully understand how pilots go about this (it seems easier to just find another alternate with traditional aids, but sometimes this may not be an option).

If anyone can clarify this for me and others, I would appreciate it.