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Alternate Airport Requirements…

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FAA Regulations, Instrument Rating

Check out the IFR alternate minimums for Des Moines.

The way I read it, you can use the ILS, LOC, VOR/DME approaches for alternate minimum planning even WITHOUT local weather being available.

Why is this the case for just these approaches, whereas local weather IS required to be available for the GPS RNAV approaches?

The FAA seem to make it clear that alternate airport local weather IS required for a particular approach to be considered for the purpose of alternate minimum planning:  "Not all airports can be used as alternate airports. An airport may not be qualified for alternate use if the airport NAVAID is unmonitored, or if it does not have weather reporting capabilities." (From the Instrument Procedures Handbook).

~PC

 

2 Answers



  1. Paul Tocknell on Dec 23, 2011

    Hi PC,

    I took a look at the DSM for filling as an alternate minimums:

    I believe the assumption is already made that local weather will be available for using the ILS and LOC for runway 5, 13, and 31.  These NAVAIDS are monitored and the airport has weather reporting capability since it is manned 24/7. 

    The note for the RNAV GPS Rwy 5, RNAV GPS 13 and RNAV GPS 31 are there because those approaches have LPV minimums (WAAS).   DSM also has a GPS RWY 23 that is not mentioned on the alternate information because it only has LNAV (MDA) minimums.  

    The FAA is allowing select GPS / LPV approaches to be used so that our air carrier / charter friends can file DSM as an alternate even if the ILS/LOC are out for runway 5, 13 and 31.  Previously many operators could never file an airport as an alternate if it was only served by GPS approaches.  Well, WAAS is changing all that so the FAA is again slowly allowing certain airports to meet the alternate airport requirements with a GPS approach as long as the local weather reporting is available.

    If you want more information look at page 2-11 of the Instrument Procedures Handbook (FAA-H-8261-1A)

    Hope that makes sense…

    Paul

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  2. John D. Collins on Dec 23, 2011

    Adding to what Paul wrote, with a WAAS GPS, RNAV approaches can satisfy the alternate requirements as long as there is local weather reporting. In many cases, the local weather has been provided by an ASOS and a note has been added to the alternate minimums on a RNAV approach to require the local weather be available.  As you indicated, in order for an approach to be considered for use as an alternate, there must be local weather reporting and the navigation facility needs to be monitored. All RNAV approaches are monitored at the national level by virtue of the WAAS system, so as long as the WAAS system is up and running, these approaches are monitored for WAAS users. 
     
    The stand alone GPS approaches predate the RNAV approaches and were designed before WAAS was available.  Over time these GPS approaches are being updated to meet the RNAV TERPS, which includes consideration for use as an alternate.  At one time there were GPS approaches that numbered in the thousands, but now that number is down to 275 remaining. So, don’t expect a GPS approach to be updated to permit use as an alternate, rather expect it to be updated to RNAV. 
     
    Regardless of the type of minimums available (LPV, LP, LNAV/VNAV, or LNAV), if the approach qualifies as an alternate, you must plan on using the LNAV approach and the alternate minimums will be 800-2 unless specifically designated higher.  Since many of these approaches will be at airports without a TAF available, you will have to use the FA (area forecast) and the IFR Sigmet Sierra for these approaches to determine if the forecast weather meets the criteria to be used as the alternate. Since there is no way without a TAF to determine if the weather meets the 800-2 criteria, this effectively requires minimum VFR conditions of 1000-3.
     
    To your original question of why there is a local weather requirement for the RNAV approaches and not for the ILS, my guess is that as Paul suggests it is assumed for the ground based navigation facilities and is redundant for the RNAV approaches.  Probably the procedure specialist is either required to make the note on RNAV approaches or just did it out of habit.
     

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