Flight diversion planning

"Diversion" sounds like a failure word, but it's not. A diversion is a routine VFR decision to land somewhere other than the planned destination because something on the original plan no longer matches reality. The pilot who diverts at the first hint of a problem usually lands with a full tank, a calm cockpit, and no story to tell. The pilot who waits is the one writing an NTSB report.

When to consider a diversion

• Weather is worse than the briefing. Ceilings dropping, visibility tightening, or thunderstorms growing along the route.
• Wind is worse than expected. Crosswind at the destination above your personal minimum, or a stronger-than-forecast headwind eating into fuel.
• Fuel reserve thinning. Anything closing in on your "land with the planned reserve" margin, not just regulatory minimums.
• Aircraft state. A rough-running engine, abnormal gauge readings, vacuum or electrical failures, a stuck flap, a partial-panel condition.
• Pilot state. Fatigue, dehydration, hypoxia, motion sickness. Any of these get worse, not better, by pressing on.
• Daylight. A delay that pushes your arrival past sunset on a day-VFR-only flight.

Pre-decide your diversion criteria

The cheapest decision is the one you made on the ground. Before you launch, write down (paper, EFB note, or scratchpad) the thresholds that will trigger a diversion:

• Minimum ceiling and visibility at the destination at ETA — usually higher than the regulatory VFR minimum.
• Maximum crosswind at the gust speed.
• Maximum tailwind.
• Fuel-on-board at the destination — the floor below which you would divert to a closer field instead of pressing on.
• Time-of-day cutoff. Land at least 30 minutes before sunset (or whatever margin your training and currency call for).

Once any one of these thresholds trips, the decision is already made — you just execute. That moves the diversion from a "should I?" judgement call (slow, emotional) to a "now I do this" action (fast, mechanical).

Picking alternates on the ground

A "real" alternate is not just an airport that fits inside your remaining fuel. It is an airport you would actually be happy to land at right now. Apply the same criteria as the original destination:

• Runway length and surface inside your personal minimums.
• Forecast weather above your personal minimums for the arrival window.
• Lighting if you might arrive after sunset.
• Fuel available for the return or onward leg, with the grade your aircraft uses, at the time you would arrive.
• FBO open at the time of arrival, especially if you need ground transportation.

The glide-aware VFR flight planner surfaces airports near the route inside your runway-length and surface filters, and the runway crosswind calculator shows the wind component for each runway given the latest METAR or the TAF at your planned ETA. Run both for any alternate you're considering, not just the planned destination.

The in-flight decision flow

When a diversion looks likely, work through the same flow every time:

1. Fly the airplane. Hand the diversion problem to your scan, not the other way around. Pitch, power, heading, altitude.
2. Verify the trigger. One bad data point isn't enough — a single low METAR can be noise, but a falling trend over two reports is real.
3. Pick the alternate. Closest acceptable airport that meets all your pre-decided criteria, not the closest airport that exists. If you're already on flight following, ask ATC for "closest VFR" — they'll usually give you a list with bearings and distances.
4. Re-run fuel and time. Distance to the alternate, headwind/tailwind on the new bearing, ETA, and fuel-on-arrival.
5. Tell ATC. If you're on flight following, " diverting to , requesting frequency change in a minute." If you're not on flight following, contact the new destination's tower or FSS before you enter their airspace.
6. Brief the approach. Pull the airport diagram, ATIS frequency, pattern altitude, expected runway, and any NOTAMs. Treat it like a planned arrival, not a surprise.
7. Land. Don't re-litigate the decision once you're committed.

Common diversion traps

• "Just 10 more miles." The destination is "almost in sight" so the temptation is to press. Run the numbers honestly — usually the diversion airport is also 10 miles away, just behind you.
• Sunk-cost reasoning. The original destination is not "free" because you've already flown most of the way. The remaining leg has the same fuel and weather risk as if you were just starting it.
• Trying to outrun weather. A line of storms moves faster than a 110-knot trainer. Divert sideways, not forward.
• Single-source weather. The on-board ADS-B picture has a latency of several minutes. Verify with a current PIREP from ATC or FSS before you act.
• Picking an alternate you've never been to with the lowest forecast ceiling on the list. A familiar field at a slightly higher minimum is often safer.

After the diversion

• Cancel your VFR flight plan if you filed one — it doesn't cancel automatically.
• Update anyone expecting you at the original destination.
• If a problem with the airplane caused the diversion, ground it until a mechanic clears it; don't depart again "to see if it does it again."
• Debrief — what was the earliest indication you should have caught, and what does that mean for your next planning session?

Related guides and tools

• VFR flight planning checklist — the upstream checklist that catches problems before launch.
• Glide distance planning guide — diversions and glide-range planning go together.
• Zulu time converter for pilots — keep clocks consistent across origin, destination, and diversion.
• Glide-aware VFR flight planner — recompute a route to a new destination quickly.
• Runway crosswind calculator — check crosswind components at the diversion field.