TAS Reality Check (Time-Speed-Distance)
Clock a known distance, get your real ground speed and — with the wind backed out — your real TAS: the pre-GPS technique that still audits every instrument.
The nm-per-minute habit scales everything: 90 kt is 1.5 nm/min, 120 is 2, 150 is 2.5. Clock two checkpoints early in every cruise and the rest of the leg's ETAs become arithmetic instead of hope.
Formula
⚠️ For flight planning and education only — verify with your POH/AFM, certified instruments and official sources. Not for primary navigation or airworthiness decisions.
Clock a known distance, get your real ground speed and — with the wind backed out — your real TAS: the pre-GPS technique that still audits every instrument.
About TAS Reality Check (Time-Speed-Distance)
Before GPS, every cross-country leg began with a ground-speed check: clock the time between two charted points, divide, and the whole flight's fuel and ETA picture snapped into focus. The habit still audits everything — a GPS fed the wrong waypoint, an ASI with a wasp in the pitot, a forecast wind that didn't show up. This calculator does the division and, with your known wind, backs out the TAS your instruments claim you have.
How to use TAS Reality Check (Time-Speed-Distance)
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula GS = distance/time × 60; TAS = GS − wind component substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use TAS Reality Check (Time-Speed-Distance)?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula GS = distance/time × 60; TAS = GS − wind component with sources cited on the page
- ✓The nm-per-minute habit scales everything: 90 kt is 1.5 nm/min, 120 is 2, 150 is 2.5. Clock two checkpoints early in every cruise and the rest of the leg's ETAs become arithmetic instead of hope.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
How far apart should checkpoints be for a good check?+
Far enough that timing error vanishes, close enough to act on the answer: 15–30 nm works well. A ±15-second timing slop over 24 nm is under 2 kt of GS error. Use crisp features — riverbank crossings, runway thresholds abeam, highway intersections — not the soft middles of towns.
My measured GS disagrees with the GPS — which is wrong?+
Neither, usually: they measure differently. Your check yields average GS between points; the GPS shows instantaneous. In gusty air or during small heading changes they legitimately differ by a few knots. Persistent disagreement beyond that means a charting/identification error on your side — or you timed to the wrong landmark.
How does this audit my airspeed indicator?+
Compute TAS here (GS minus known wind), then compare with CAS/√σ from your indicated speed (our TAS calculator). A gap beyond ~5 kt with a trustworthy wind means the pitot-static system or the wind estimate is lying. Flying reciprocal headings cancels the wind entirely — that's our GPS four-leg tool, this technique's modern descendant.
What's the nm-per-minute trick instructors keep mentioning?+
Divide knots by 60 and navigate in miles per minute: 120 kt = 2 nm/min means a 14-nm leg is 7 minutes, no calculator. It converts every enroute mental problem — descent points, holding timing, diversion ETAs — into single-digit arithmetic. This tool reports your pace in nm/min for exactly that workflow.
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