Glide distance planning guide

Every cross-country in a light single is, at some level, a planning exercise around glide. If the engine stops, how far can you reach? Does that distance cover a runway, a known landing area, or just a field you'd rather not pick blind from the air? Planning the answer to that question on the ground means you can fly the leg with options instead of guessing in the moment.

What "glide ratio" really means

The glide ratio is the horizontal distance you cover in still air per unit of altitude lost, at best-glide speed. A 10:1 glide ratio means 10 nautical miles forward for every 6,000 feet of altitude — roughly the published number for a typical light single. Heavier and dirtier aircraft glide less; clean retractables glide more.

Glide ratio is published in the POH/AFM for best-glide speed and at the published configuration. Two things move the published number around in real life:

• Weight. The best-glide speed changes with weight (some POHs publish a speed table). The glide ratio is roughly constant if you fly the right speed for the weight.
• Configuration. Flaps, gear, propeller pitch, and a windmilling propeller all hurt the ratio. Stay clean if you're trying to glide somewhere.

Still-air glide distance

The arithmetic is straightforward:

Still-air glide distance (NM) = altitude above field (feet)
                                ÷ 6076 (feet per NM)
                                × glide ratio

At 6,000 feet AGL with a 10:1 ratio, that's 6000 / 6076 × 10 ≈ 9.9 NM. Most pilots round to 1.5 NM per 1,000 feet AGL at 10:1, which is conservative enough to use in your head while planning.

Add wind

Wind has a big effect. A 15-knot headwind toward your candidate landing field cuts a 10:1 ratio toward roughly 8:1 in the headwind direction; a 15-knot tailwind extends it to 12:1 or more. A cross-country that looks "in glide" in still air can look very different on a 25-knot wind day.

The full correction is the descent time at best-glide speed multiplied by the headwind/tailwind component along the bearing to the field. Pilots usually use a rule of thumb:

• For every 10 knots of headwind toward the field, knock roughly 10% off the still-air glide distance toward it.
• For every 10 knots of tailwind toward the field, add roughly 10%.

The Aero Companion glide-aware VFR flight planner does this projection automatically. For every sample point along the route it projects the local wind onto the bearing toward each candidate landing field and scales that field's glide ring. The scaling is clamped to a ±35% band so a single freak forecast can't dominate the picture, and the assumptions panel tells you which wind source was used (NOAA FB/FD winds aloft, or METAR fallback if the upper-air product wasn't available).

Safety margin

Never plan to land on the last foot of the published glide ring. Real-world glide performance is worse than the POH/AFM number because of:

• Pilot reaction time — engine failure recognition, identify-best-glide, pick a field.
• Configuration changes — flaps, gear, propeller — that you may not get fully back to clean.
• Bank angle for turns toward the field.
• Density altitude and aircraft weight.

A common convention is to subtract a safety margin (often 10–20%) off the theoretical maximum, then plan to be inside that ring. The flight planner uses a similar safety margin by default and surfaces it in the assumptions panel so you can sanity-check it before you act on a number.

Worked example: a 100 NM cross-country

You're planning a 100 NM cross-country in a Cessna 172 at 8,500 feet MSL. Terrain along the route is flat at about 500 feet MSL, so AGL is roughly 8,000 feet. Glide ratio: 9:1. Wind aloft at altitude: 270° at 20 kt.

1. Still-air glide: 8000 / 6076 × 9 ≈ 11.8 NM. Apply a 15% safety margin and you're planning around a 10 NM ring.
2. Direction: the route bears 090°. Wind is 270° at 20 kt — a near-direct tailwind. Glide downwind looks excellent; upwind, toward any field behind you, the wind eats a chunk of the ring.
3. Field coverage: drop your finger every 10 NM along the route and check that at least one usable runway is within the wind-adjusted ring. Where the answer is "no," consider a slightly different route, a higher cruise altitude, or accept a known gap (and brief the off-airport plan for that leg).

Things that aren't in the glide ring

• Terrain. A 10 NM ring across a ridge is not 10 NM of glide. The flight planner does not model terrain between the aircraft and the candidate field — assume it could shorten the usable distance.
• Airspace. A "reachable" airport that sits inside restricted airspace is not actually reachable. Cross-check against the sectional.
• Time of day. A daytime forced landing on a familiar runway is different from a night forced landing onto an unlit field.
• Surface and length. Set a minimum runway length and surface that you'd actually be comfortable landing on power-off. The flight planner filters on both.

When the gaps are unavoidable

Some routes will have legs that are not glide-safe. Open water, long mountain passes, and desert crossings are examples. The plan for those legs is not "ignore it" — it is:

• Pick the cruise altitude and route that minimises the gap.
• Brief the off-airport plan: best-glide speed, where you'd put it down by terrain, and what you'd do with the radios and squawk.
• Consider PFDs/raft, survival kit, and other equipment appropriate to the terrain.
• Reset personal minimums if the day-of conditions push the gap past what you're willing to fly.

Related guides and tools

• VFR flight planning checklist — where glide-safety fits into the full preflight flow.
• Flight diversion planning — how to think about diversions when the glide picture changes in flight.
• Glide-aware VFR flight planner — wind-aware route planning that keeps a runway in glide range.
• Runway crosswind calculator — pick a runway by crosswind component when you do divert.