Top of Descent
When to start down. Distance to TOD, time at your descent rate, actual descent angle, and a 3° field-rule sanity check. Same math the avionics uses — wrapped in something you can pull up on your phone before the STAR.
Inputs
Where you are right now.
Usually pattern altitude (TPA) for VFR, or initial-approach-fix altitude for IFR.
Use indicated GS from the GPS / EFB, not TAS or IAS.
500 fpm is a comfortable piston default. Jets typically use 1500-2500.
Verdict
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Enter current altitude, target, GS, and descent rate
Field rule: altitude to lose ÷ 300 = NM out for a ~3° path.
How to read this
Steeper than 3° means you'll need to pull power early (or extend flaps / gear on profile) to get down without overspeeding. Shallower than 3° means you have margin — but if winds pick up or GS shifts, you'll arrive high at the field.
About this calculator
Pure geometry — no atmospheric model needed. Time = altitude ÷ rate. Distance = (time / 60) × ground speed. Angle = atan(altitude ÷ (distance × 6076)). The 3° rule (altitude ÷ 300 = NM) is a field-tested shortcut that comes within ~0.2° of the true 3° glideslope and matches the ILS standard.
Cross-check against ATC crossing restrictions and any VNAV path your avionics is flying. Not a replacement for a proper descent plan on RNAV / STAR procedures.
Trim
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Flight training management for independent CFIs.