When filing an IFR flight plan, part of the process is determining whether or not an alternate airport is required. An alternate airport is required when the following conditions exist(as is outlined by the FAA in 91.169 (b)):
The weather conditions at the destination airport
- From 1 hour before your arrival time to 1 hour after your estimated time of arrival, the weather conditions are forecast to be below
- 2,000 Feet AGL and/or
- 3 statute miles visibility
Let’s paint a scenario. You are traveling from KSAT (San Antonio International Airport) to KHBV (Jim Hogg County Airport in Hebbronville, TX). You start to file your flight plan and get down to the space where you put your alternate in. Since Laredo (KLRD) is the closest airport with a TAF, you check Laredo’s TAF and see that the forecast conditions there at your ETA are ceilings 1,500 and visibility of 2sm.
Based on this information, you need an alternate airport. Now, the process of finding one. In Part 91.169 (c), the forecast conditions at the alternate airport must be at or above:
- 600 Feet AGL and 2sm visibility for a precision approach, or
- 800 Feet AGL and 2sm visibility for a non-precision approach
Alright, now we have some guidance. Laredo is the nearest airport to KHBV, and we know the forecast from the above TAF showing the conditions are forecast to be above the alternate minimums outlined in Part 91, so let’s pick Laredo. All done?
Not quite. A lot of airports have Non-Standard Alternate Minimums. How do you figure out if they do? The easiest way is to look at any approach plate for the airport. In the notes section of the government plates, there will be a black triangle with an A in it. That means there are non-standard alternate minimums published for that airport (in layman’s terms, different than the ones stated above in Part 91).
Now the question is, where do you find those non-standard alternate minimums? On Foreflight:
- Go to the Airports page
- Tap the Procedures button
- Tap the Arrival button
- Tap the Alternate Minimums option
This brings up the IFR Alternate Minimums document for all the airports with non-standard alternate minimums in that area. Scroll through to find Laredo.
As you can see, there are several notes there concerning the different approaches into Laredo. For our example, we’ll say the winds are out of the south and we are planning on flying the ILS 17R if we cannot get into KHBV and have to come to Laredo. The note there is that the Alternate Minimums for the ILS 17R are actually 700 AGL ceilings and 2sm instead of the above state 600 AGL ceilings and 2sm, the procedure is NA if the tower is closed, and NA if the local weather isn’t received.
What does this tell us? If the forecasted ceilings at Laredo were below 600 AGL instead of 700 AGL, we would not be able to use LRD as an alternate airport if we were planning on flying the ILS 17R. The RNAV approaches are all fair game, so a GPS equipped aircraft would have no problem.
On top of that, some approaches at a certain airport are not authorized to be used in the case of the airport being used as an alternate. At the Galveston airport (KGLS), the ILS 14 is NA as an alternate procedure, but all the RNAV approaches are available.
Picking an alternate seems simple at first, but there are actually a lot of things to consider in the process.
Need help remember all this stuff? AOPA has put out a kneeboard sheet that helps all IFR pilots remember those important things when it comes to IFR flying. Check it out here.