{"openapi":"3.1.0","info":{"title":"Density Altitude API","version":"1.0.0","description":"Aviation atmosphere maths as an API, computed locally and deterministically using the exact International Standard Atmosphere relations — the numbers a pilot, dispatcher or flight-planning tool needs before take-off, not a rough rule of thumb. The density-altitude endpoint turns the field elevation, altimeter setting and outside air temperature into the pressure altitude (elevation + (29.92 − setting) × 1000) and then the density altitude — the altitude the air actually feels like to the wings and engine — computed from the true ISA density ratio rather than the approximate 120-foot-per-degree rule, with the ISA temperature deviation: on a hot, high day the density altitude soars, robbing lift and thrust and lengthening the take-off roll, the classic mountain-airport hazard. The true-airspeed endpoint gives TAS from calibrated airspeed as CAS ÷ √(density ratio), so the navigator gets the real speed through the air that climbs above the indicated reading with altitude and temperature. The isa endpoint returns the standard-atmosphere temperature, pressure, pressure and density ratios and the speed of sound at any altitude in the troposphere — the reference every altimeter, performance chart and engine rating is built on. Everything is computed locally and deterministically, so it is instant and private. Ideal for flight-planning and EFB apps, drone and UAV tools, aviation weather dashboards, and aerospace-engineering utilities. Pure local computation — no key, no third-party service, instant. Troposphere (≤ 36,089 ft); incompressible TAS. 3 compute endpoints. For the speed of sound and Mach use a Mach-number API; for runway wind components a crosswind API.","contact":{"name":"PremiumApi","url":"https://www.oanor.com/by/premiumapi"}},"servers":[{"url":"https://api.oanor.com/densityaltitude-api","description":"oanor gateway"}],"tags":[{"name":"Atmosphere"},{"name":"Meta"}],"components":{"securitySchemes":{"oanorKey":{"type":"apiKey","in":"header","name":"x-oanor-key","description":"Get your key at https://www.oanor.com/developer/keys"}}},"security":[{"oanorKey":[]}],"paths":{"/v1/density-altitude":{"get":{"operationId":"get_v1_density_altitude","tags":["Atmosphere"],"summary":"Pressure & density altitude","description":"","parameters":[{"name":"field_elevation_ft","in":"query","required":true,"description":"Field elevation (ft)","schema":{"type":"string"},"example":"5000"},{"name":"altimeter_inhg","in":"query","required":false,"description":"Altimeter setting (inHg, default 29.92)","schema":{"type":"string"},"example":"29.92"},{"name":"oat_c","in":"query","required":true,"description":"Outside air temperature (°C)","schema":{"type":"string"},"example":"25"}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"Pressure altitude = field elevation + (29.92 − altimeter setting) × 1000. Density altitude is the altitude the air 'feels like' to the wings and engine — computed here exactly from the ISA density ratio, not the rough 120-ft-per-degree rule. On a hot, high day the density altitude soars: less lift, less thrust and a longer take-off roll, the classic mountain-airport hazard. Above the ISA temperature density altitude exceeds pressure altitude.","inputs":{"oat_c":25,"altimeter_inhg":29.92,"field_elevation_ft":5000},"isa_temp_c":5.1,"density_ratio":0.8041,"isa_deviation_c":19.9,"density_altitude_ft":7263,"pressure_altitude_ft":5001},"meta":{"timestamp":"2026-06-06T23:53:54.746Z","request_id":"3dd1f7b8-bf3c-4b0c-a9c3-0be6c2e05f71"},"status":"ok","message":"Density altitude","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/isa":{"get":{"operationId":"get_v1_isa","tags":["Atmosphere"],"summary":"ISA standard atmosphere at an altitude","description":"","parameters":[{"name":"altitude_ft","in":"query","required":true,"description":"Altitude (ft, ≤ 36089)","schema":{"type":"string"},"example":"10000"}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"The International Standard Atmosphere: from 15 °C and 1013.25 hPa at sea level the temperature falls 1.98 °C per 1,000 ft up to the tropopause (36,089 ft), and pressure and density follow from it. It is the reference every altimeter, performance chart and engine rating is built on — the real atmosphere differs, which is exactly why pressure and density altitude exist. This endpoint covers the troposphere.","inputs":{"altitude_ft":10000},"temp_c":-4.81,"pressure_hpa":696.82,"density_ratio":0.7385,"pressure_ratio":0.6877,"speed_of_sound_kt":638.3},"meta":{"timestamp":"2026-06-06T23:53:54.833Z","request_id":"e1ab2ead-150b-43d8-a1ba-0fa2b390b52c"},"status":"ok","message":"ISA atmosphere","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/true-airspeed":{"get":{"operationId":"get_v1_true_airspeed","tags":["Atmosphere"],"summary":"True airspeed from CAS","description":"","parameters":[{"name":"cas_kt","in":"query","required":true,"description":"Calibrated airspeed (knots)","schema":{"type":"string"},"example":"100"},{"name":"pressure_altitude_ft","in":"query","required":true,"description":"Pressure altitude (ft)","schema":{"type":"string"},"example":"5000"},{"name":"oat_c","in":"query","required":true,"description":"Outside air temperature (°C)","schema":{"type":"string"},"example":"25"}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"True airspeed = calibrated airspeed ÷ √(density ratio): thinner air reads low on the airspeed indicator, so TAS climbs above CAS with altitude and temperature (a rough 2 % per 1,000 ft). This is the incompressible form — fine for light aircraft; near and above the transonic range compressibility adds a further correction. Use TAS for navigation and ground-speed work; the wings still only feel CAS.","inputs":{"oat_c":25,"cas_kt":100,"pressure_altitude_ft":5000},"density_ratio":0.8041,"true_airspeed_kt":111.5},"meta":{"timestamp":"2026-06-06T23:53:54.917Z","request_id":"eb3fee5f-9711-4b9a-b2b3-c0f9d296bed2"},"status":"ok","message":"True airspeed","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/meta":{"get":{"operationId":"get_v1_meta","tags":["Meta"],"summary":"Spec","description":"","parameters":[],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"notes":"ft, inHg, °C, knots. PA = elev + (29.92 − altimeter)×1000; density altitude from the exact ISA density ratio; TAS = CAS/√σ. Troposphere (≤ 36,089 ft). For the speed of sound / Mach use a Mach-number API; for runway wind components a crosswind API.","service":"densityaltitude-api","endpoints":{"GET /v1/isa":"ISA standard-atmosphere properties at an altitude.","GET /v1/meta":"This document.","GET /v1/true-airspeed":"True airspeed from calibrated airspeed, pressure altitude and temperature.","GET /v1/density-altitude":"Pressure altitude, ISA deviation and density altitude."},"description":"Aviation atmosphere maths: pressure & density altitude from altimeter and temperature, true airspeed from CAS, and the ISA standard atmosphere."},"meta":{"timestamp":"2026-06-06T23:53:54.996Z","request_id":"114b02a7-c2aa-4b9f-8a6c-29644b6e88ca"},"status":"ok","message":"Meta","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}}},"x-oanor-pricing":[{"slug":"free","name":"Free","price_cents_month":0,"monthly_call_quota":6200,"rps_limit":2,"hard_limit":true},{"slug":"starter","name":"Starter","price_cents_month":1090,"monthly_call_quota":68000,"rps_limit":6,"hard_limit":true},{"slug":"pro","name":"Pro","price_cents_month":3450,"monthly_call_quota":284000,"rps_limit":15,"hard_limit":true},{"slug":"mega","name":"Mega","price_cents_month":10600,"monthly_call_quota":1390000,"rps_limit":40,"hard_limit":true}],"x-oanor-marketplace-url":"https://www.oanor.com/api/densityaltitude-api"}