When Do You Need To File An Alternate Under IFR? (2024)

You're planning an IFR flight, and the weather at your destination is marginal. Do you need to file an alternate? And if so, what are the weather minimums for your alternate airport?

We'll cover both topics here, and we'll show you some quick tips for alternate planning if you're using ForeFlight.

First Off, When Do You Need to File An Alternate?

Simply put, you always need to file an alternate airport unless...

• The airport has an instrument approach, AND...
• Weather reports and forecasts indicate that from 1 hour before to 1 hour after your ETA (at the listed destination) the ceiling will be at least 2,000' AGL and the visibility will be at least 3 SM.

It's called the 3-2-1 rule, and it's the easiest way to remember the regulation.

To recap, if the weather at your destination isn't at least 3 SM of visibility and 2000' AGL ceilings from 1 hour before to 1 hour after your ETA, you need to file an alternate.

Planning Your IFR Alternate

So if you need an alternate airport, how good does the weather at your alternate need to be?

For your alternate airport to meet the requirements of FAR 91.169, the weather conditions at the ETA must meet or exceed:

• If a usable precision approach is available: 600' ceilings AND 2 SM of visibility.
• If only a non-precision approach is useable: 800' AND 2 SM of visibility.
• If no instrument approaches are available: Descent from the MEA and landing must be conducted under basic VFR.

Planning For The Actual Alternate Minimums

In the real world, not all airports follow the standard minimums we just listed above here. If that's the case, the airport has nonstandard alternate minimums. So how do you find those alternate minimums?

If you're using Jeppesen charts, it's incredibly easy. The airport's alternate minimums, standard or nonstandard, are listed on the airport's 10-9 page.

For example, take a look at Daytona Beach's alternate minimums below, which we've highlighted in yellow at the bottom of the 10-9 page:

If you're able to use the ILS to runway 7 at KDAB, your alternate minimum weather can be as low as 700' ceilings and 2 SM visibility. That's not quite as low as standard precision alternate minimums, but it is close.

However, if you can't plan for that approach (for example, the ILS Rwy 7 is inoperative), you need to pick another approach further to the right on the chart. Each column to the right has one or more approaches, and the alternate minimums associated with that approach listed below.

If you were not GPS equipped in your plane, and the ILS Rwy 7 was out of service, you'd have to plan for the ILS Rwy 25R alternate minimums of 1100' ceilings and 2 SM visibility (for Category A and B aircraft).

What About FAA Charts?

If you're using FAA charts, finding alternate minimums is a 2-step process.

First, if the airport has nonstandard alternate minimums, you'll see this symbol on the approach chart for the airport:

Next, to find out what the alternate minimums actually are, you need to turn to the chart supplement.

If you're using ForeFlight, you can click on the "alternate minimums" tab under "arrival procedures." Sorted by city name, you'll find the new weather minimums you must use to determine if an airport is eligible to file as an alternate.

Many airports will have nonstandard alternate requirements due to terrain considerations, and they may vary by aircraft approach category. In rare cases, an airport might not be available as an alternate, often because there's no on-airport weather reporting.

What If There Isn't A TAF At Your Destination Or Alternate?

Using a TAF to determine the weather conditions at your destination and alternate is the most common way pilots plan an IFR flight.

But what happens if your destination or alternate doesn't have a TAF?

In the past, you had to use the Area Forecast (FA) from NOAA's Aviation Weather Center. Now that the FA has been officially discontinued for the contiguous United States, you'll need to use the Graphical Area Forecast (GFA). Use the "Ceiling/Visibility" tab and the Zulu time sliding bar to determine weather conditions around your arrival.

Fuel Requirements

Next up, you need to make sure you have enough fuel for your destination and alternate airport.

Day or night, you need enough fuel to (FAR 91.167)...

• Fly to your intended destination.
• Fly from the destination to the alternate (if required).
• Fly for an additional 45 minutes at normal cruise speed (minimum).

It's Not Just About Weather

Alternate planning shouldn't be based on weather alone. There are other factors that you should include during your planning as well:

• ATC Services Available
• Transportation
• Lodging
• Nearby Restaurants
• FBO Services
• Passenger Requirements
• Maintenance
• Runways and Conditions

You Have To Divert. Now What?

Whether you're going missed off an approach at your destination or just diverting early, you're not required to fly to your filed alternate. Filing an alternate on your IFR flight plan is for planning purposes only, and once you're airborne, you can change your alternate if you need to.

That being said, just because you don't have to fly to an alternate doesn't mean you shouldn't put a lot of consideration into your choice. Having a reasonable "Plan B" in mind is important when you actually need to divert. Instead of fumbling around the co*ckpit searching for nearby diversion options, you'll have an easy go-to strategy.

Alternates Made Easy: ForeFlight's Alternate Advisor

Now that we've covered the ins-and-outs of alternate planning, there's a tool in ForeFlight that makes your alternate planning easy. It's called Alternate Advisor, and here's a short clip that explains how to use it:

Have you ever diverted to your alternate? Tell us about it in the comments below.

Why do we fly with Jeppesen charts? They make planning and flying IFR flights quicker and easier. Learn more about their advantages over FAA charts here.