Top of descent API

Computes top-of-descent distance, required descent rate (fpm) and time for a target altitude loss at a given gradient/angle and ground speed. Answers 'How many miles out do I start a 3-degree descent from FL350?', 'What fpm do I need at 450 kt?'.

Price$0.04per request

MethodPOST

Route/v1/nav/top-of-descent

StatusLive

MIME typeapplication/json

Rate limit120/minute

Cache0s public

aviationtop-of-descenttoddescentglidepathfpmgradientarrival

API URLhttps://x402.hexl.dev/v1/nav/top-of-descent

Integration docs

Example request

{
  "altitudeToLoseFt": 30000,
  "groundSpeedKt": 450
}

Example response

{
  "distanceToTodNm": 94.21,
  "descentRateFpm": 2388,
  "descentTimeMin": 12.6,
  "descentGradientPercent": 5.24,
  "descentAngleDeg": 3,
  "interpretation": "Start descent 94.2 nm out; 2388 fpm at 450 kt GS for a 5.2% (3 deg) path."
}

Input schema

{
  "type": "object",
  "required": [
    "altitudeToLoseFt",
    "groundSpeedKt"
  ],
  "properties": {
    "altitudeToLoseFt": {
      "type": "number",
      "examples": [
        30000
      ]
    },
    "descentGradientPercent": {
      "type": "number"
    },
    "descentAngleDeg": {
      "type": "number"
    },
    "groundSpeedKt": {
      "type": "number",
      "examples": [
        450
      ]
    }
  }
}

Output schema

{
  "type": "object",
  "additionalProperties": true
}