Helicopter IFR Alternate Minimums

KPDX 311053Z 01004KT 4SM OVC008 15/14 A3006 RMK AO2 SLP179

Take a look at the METAR above. How can you tell if you will need to file an alternate airport if wanting to fly to KPDX on an IFR flight plan in a helicopter?

Figuring out the rules of filing for an alternate airport is a struggle helicopter pilots keep coming back to. It's not just students who struggle, as it's far from most commercial helicopter operations which operate in IFR conditions, which means general IFR knowledge often is weak or misunderstood with the majority of helicopter pilots.

To answer the question above, your first action should be finding out which approach we're talking about. Let's pick the ILS OR LOC RWY 10L at KPDX.
Helicopter IFR alternate minimums
Next, let's refer to FAR 91.169(C)(1)(ii):
For helicopters. At the estimated time of arrival and for 1 hour after the estimated time of arrival, the ceiling will be at least 1,000 feet above the airport elevation, or at least 400 feet above the lowest applicable approach minima, whichever is higher, and the visibility will be at least 2 statute miles.

Think of it this way: when filing an IFR flight plan, you should always plan to file an alternate. Legally, however, we don't have to file one if the following is true:
Helicopter IFR alternate airport

KPDX 311053Z 01004KT 4SM OVC008 15/14 A3006 RMK AO2 SLP179

Looking back at the METAR, we can see that what we're looking for is the ceiling of 800 ft. and the 4 SM visibility. Referring to the approach plate, we can determine the airport elevation of 31 ft. First we need to find out which provides the highest ceiling - A or B.

A - The ceiling is 800 ft. above the field elevation.
B - The ceiling is 537 ft. above the ILS 10L (800-263).
Having determined A is the highest of the two, and A not meeting the requirement of having the ceiling 1000 ft. above the airport elevation, it is safe to assume that it's necessary to file an alternate airport on the IFR flight plan.

The above "test" assumes an Instrument Approach Procedure (IAP) is available at the airport. If there is no IAP, then an alternate must be filed regardless of the weather conditions.

The alternate airport

Just as the airport of intended landing, KPDX, has certain requirements under the alternate airport rules, so does the alternate airport. Let's take a look at FAR 91.169(C)(2)(ii):

For helicopters: Ceiling 200 feet above the minimum for the approach to be flown, and visibility at least 1 statute mile but never less than the minimum visibility for the approach to be flown.

Helicopter IFR alternate airport weather

In case of no IAP at the alternate airport, then you must be able to visually descent from the MEA to land in VFR conditions.

Give the table below a good look and have it make sense to you. Remember, if you're ever in doubt about filing an alternate - just file one.

Helicopter-IFR-alternate-airport-full-chart.webp

There's a little more to look into before we pick a specific alternate airport. The AIM 1-1-17 5 (C) describes:

"... may file based on a GPS-based IAP at either the destination or the alternate airport, but not at both locations."

This means if you are planning to fly a GPS approach to your primary airport, then the alternate airport must have a non-GPS approach. You cannot file for two GPS approaches!

Furthermore, the AIM states that you can file for the following GPS-approaches regarding an alternate airport:

  • LNAV
  • LNAV/VNAV

That's right, you are not permitted to fly an LPV to your alternate airport regardless of what your intended approach type originally is.

Fuel requirements

Lastly, we need to take a look at our fuel. This one is simple compared to the rest of it. Refer to FAR 91.167.

Helicopter IFR alternate fuel requirements