top of page
Search

Filing a Destination Alternate

  • Writer: Tizi
    Tizi
  • Apr 6
  • 3 min read
"I checked the non-standard alternate minimums" - No one ever


When filing an IFR flight plan, one must consider whether the weather at destination is sufficiently "good" to comfortably guarantee a successful approach. Lucky for us, the FAA prescribes very clearly the weather minimums required to "be comfortable". If such level of comfort is not achievable, an alternate airport must be selected (and filed).


Do I need to file an alternate?


Per 14 CFR 91.169, we need to file an alternate destination airport if the following conditions are not met (we call it the 1-2-3 rule):


  1. 1 hour before to 1 hour after the Estimated Time of Arrival (ETA)

  2. forecasted ceilings are at least 2,000 ft

  3. forecasted visibility is at least 3 SM


What are the requirements for the alternate?


We cannot choose just any random airport. The alternate airport has weather requirements as well, which need to be forecasted for the estimated time of arrival at that airport:



So, if we have a precision approach at the alternate (i.e., an ILS), then we need at least 600 ft ceilings and 2 SM visibility. If we have a non-precision approach (e.g., LPV, LNAV, etc.), then we need at least 800 ft ceilings and 2 SM visibility. If the airport has no approach at all, we need to be able to descend from the MEA to the runway under VFR (not VMC).


Only Using GPS?


Things get a bit more complicated if you only want to use GPS approaches at your destination and alternate. Here are the extra rules:

  1. If you have a non-WAAS GPS (kinda rare, but possible), you can file a flight plan based on GPS approaches at either the destination or the alternate, but not both. So let's say that you don't have a WAAS GPS. Your destination only has RNAV approaches. Well, your alternate must have VLOC approaches to be used as such.

  2. If you have WAAS with Baro-VNAV, you can use GPS at both destination and alternate, but for the alternate, you must plan on using LNAV/VNAV or RNP 0.3 lines of minima (note, the RNP requires training/authorization/etc).

  3. If you have WAAS without Baro-VNAV, you can use GPS at both destination and alternate, but for the alternate, you must plan on using LNAV or circling lines of minima.

If you cannot meet these conditions, then your destination and alternate must have both RNAV (GPS) and VLOC approaches.


Non-Standard Alternate Minimums?


Once you've figured out all the stuff above, you need to check your selected approach for your alternate and verify if there are any non-standard alternate requirements.


Let's assume you are planning the ILS 10 at KSAV as your alternate destination approach (given your equipment on board). You look at the plate and you notice there is an A triangle symbol in the notes section:



That indicates that non-standard alternate requirements exist. These outrule the requirements in 91.169 (1-2-3 rule). If we look at the alternate minimums page, we see that SAV has the following requirements:



The ILS or LOC Rwy 10 has the footnotes 1 and 2, which read:

  1. NA when control tower closed

  2. LOC Cat D 800-2 1/4


That means that I cannot choose that approach if the tower is closed. And if I am a cat D airplane (clearly not a Piper Cherokee), then my weather minimums to shoot the LOC approach are 800 ft ceilings and 2 and 1/4 SM visibility (contrary to the 2 SM visibility prescribed by 91.169).


It's Only for Planning!!!


A final word - remember that this is for PLANNING only! If you determined that your airport should have your alternate weather minimums, it doesn't mean that you cannot attempt an approach if weather has deteriorated by the time you're airborne. These considerations are only required for planning, not execution.


When do I really need to go to the Alternate?


This is a 5-star question. Think about it. If you can't figure it out, ask Tizi.


Other considerations


  • Fuel Planning. Per the regulations, you need fuel to reach your alternate from your destination. Be conservative! How will you get to your alternate? Consider airways, navigating to an Initial Approach Fix (IAF), and executing an approach! So your fuel requirements will be greater than just a straight line!

  • Alternate Locations. If possible, position your alternate on your original route. That is because you will have the opportunity to overfly the alternate and verify first-hand what the weather is like. Many times this is not an option - so just use it as a consideration.


 
 
 

Comments

bottom of page