Bugout Times – When to Divert to the Alternate Airport

IFR Charts

Without taking fuel burn into consideration, you can wind up in a situation where you no longer have enough fuel to fly to the alternate – and perhaps even the destination.As an instrument rated pilot, you know all about flying holding patterns and computing entries. But you can’t fly around in a holding pattern all day, sooner or later you’ll have to decide when to bug out and go to the alternate. It’s better to make this decision sooner than later, here’s how.

The fundamental problem with holding patterns is fuel. Here you are burning gas, but getting no closer to the airport. Without taking fuel burn into consideration, you can wind up in a situation where you no longer have enough fuel to fly to the alternate – and perhaps even the destination.

We need to put first things first: always fly the airplane. This is especially important in single pilot IFR with no autopilot. You don’t want your fuel planning to distract you from making a safe holding pattern entry or worse.

Determining your bug out time is as simple as 1, 2, 3.

1. Plan the diversion from the holding fix to the alternate airport.

This one should be easy – you were trained for it as a private pilot. Find a radio navigation As a pilot, you should feel uneasy about landing with anything less than your required reserve fuel, (45 minutes for IFR flight). That’s why I suggest planning to divert just before your fuel on board equals BURN + Reserveaid and course that will get you  to that alternate. You will also need to figure out the  distance to the alternate. All of this is almost automatic with the use of modern GPS systems, which typically provide a heading and distance at the very least.

2. Get the fuel burn to the alternate.

You might think that you’ve already done this in the preflight planning phase, but be careful. The alternate airport fuel burn on your flight plan is probably based on flying from the destination to the alternate. Alternate fuel burn will be different from the holding fix and this is especially critical if the alternate airport is beyond the destination.

Even Spock is confused by the whiz-wheel E-6B flight computer!

"Captain, this primitive flight computer is most illogical"

Since most private pilots think of fuel on board in terms of minutes, this is actually pretty simple. Just spin the E6B flight computer (or cheat by looking at your GPS) and figure out the time from the holding fix to the alternate.

We’ll refer to this as BURN in step 3.

3. Figure out the bug out time.

As a pilot, you should feel uneasy about landing with anything less than your required reserve fuel, (45 minutes for IFR flight). That’s why I suggest planning to divert just before your fuel on board equals BURN + Reserve.

This sets us up to land with 45 minutes of gas in the tank at the alternate airport.

Continue to page two for an example ->


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About the author
Pat Flannigan is a professional pilot and aviation blogger. He has been flying for fifteen years and is currently working as an airline pilot in the United States.

2 Replies to Bugout Times – When to Divert to the Alternate Airport

  1. Harrison says:

    All good info, Pat, and well presented. Imagine the guys landing at Tokyo when the earthquake closed the field. Probably some serious computing going on.

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