Course, distance, ETE

Once you've picked a field, you need three numbers — a heading, a distance, and a time — and you need them now, in the air, without the flight-planning desk.

Estimating the course

Use whatever's fastest and to hand, roughly in this order:

• GPS direct-to — instant course and distance (verify it, below).
• Plotter — lay it on the chart from your present position to the field and read the magnetic course.
• Rule-of-thumb / landmarks — "the field's off my left wing about 30°, so roughly a 300 heading." Crude, but enough to start the turn.

You don't need precision to begin — you need a reasonable heading now and a refined one a minute later. Turning roughly the right way immediately beats a perfect course computed while you drift.

A handy in-flight shortcut for the heading: locate the field on the chart relative to a feature you can see, and read the rough bearing off the compass rose around a nearby VOR — it's already aligned to magnetic north (from VI.A.K3). You're not after a degree-perfect course, just "northwest-ish, call it three-one-zero," so the nose is moving the right way while you refine the rest.

Distance, ETE, and fuel

• Distance ÷ groundspeed = ETE. A field 24 NM away at 120 kt is about 12 minutes.
• Then the question that actually matters: fuel required vs. fuel aboard. Twelve minutes of flight plus your reserve — do you have it? If you're diverting for fuel, this is the entire point.
• Mind the wind: diverting into a headwind stretches both the ETE and the fuel burn well past a no-wind estimate, so add margin when the wind's against you.

Put numbers on it. That 24-NM field at 120 kt is about 12 minutes, and at roughly 8 gph that's about 1.6 gallons to get there. If you're carrying 6 gallons and a 45-minute night reserve eats about 4.5 gallons, you've got only ~1.5 gallons of working margin — tight enough that a closer field, or one directly with fuel, becomes the obvious call. The numbers turn "I think I can make it" into "I know I can, with this much to spare" — or into "no, pick something closer."

Run the whole loop below — situation, field, three numbers, verdict. The scenarios are built so the nearest field and the right field are rarely the same dot on the chart.

The GPS shortcut and its trap

The GPS "nearest" / "direct-to" function is the fastest tool you have — and the most willing to hurt you. The "nearest airport" page will cheerfully send you direct to a private grass strip with no fuel and no services, straight across a restricted area, or over a mountain ridge you can't outclimb. It optimizes for distance, not suitability or safety.

So use it, but verify three things: is the field public and usable, does it have what you need, and is the straight-line route actually flyable around terrain and airspace? The magenta line is a suggestion, not a plan — the wind-triangle and pilotage skills from VI.A.K1 are what turn it into one.

And cross-check the box against reality: glance at the GPS distance and ETE, then sanity-check them against the chart and your groundspeed. A "direct-to" that reads 60 miles when the field looked 20 away on the chart means you selected the wrong identifier — catch it now, on the ground of your attention, not halfway through the wrong diversion.