{
  "address": "3bae963dec6e5bb4d342209425f7e54b",
  "category": "other",
  "question": "Using the ICAO Standard Atmosphere formula, what is the pressure altitude at a station pressure of 1013.25 hPa?",
  "answer": "0.00 ft",
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  "madeAt": "2026-09-30T22:39:30.722Z",
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  "sources": [
    {
      "label": "ICAO Standard Atmosphere barometric formula for pressure altitude",
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    }
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  "source": {
    "kind": "standard",
    "value": "ICAO Doc 7488, Manual of the ICAO Standard Atmosphere.",
    "retrieved_utc": "2026-09-30T19:55:00Z"
  },
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  "deck_id": "method-deck",
  "deck_title": "Method Deck",
  "method": {
    "name": "Pressure altitude from station pressure (ISA)",
    "version": "1",
    "source_url_or_file": "methods/pressure-altitude-standard-atmosphere.cjs",
    "sha256_of_method_file": "5ab25ee93d27df77ed5dddb955d32320f489e4b8e48bee109ff7181ceab10f7e"
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  "method_deck": {
    "inputs": [
      {
        "name": "station_pressure_hpa",
        "type": "number",
        "unit": "hPa (millibars)",
        "required": true,
        "description": "Station (unadjusted) barometric pressure.",
        "min": 300,
        "max": 1100
      }
    ],
    "outputs": [
      {
        "name": "pressure_altitude_ft",
        "unit": "feet",
        "description": "Pressure altitude."
      }
    ],
    "steps": [
      "ISA barometric formula: PA = (1 - (P / 1013.25)^0.190284) * 145366.45, where P is station pressure in hPa and PA is pressure altitude in feet, and 1013.25 hPa is the ICAO standard sea-level pressure.",
      "Round to 2 decimals.",
      "This assumes the ICAO Standard Atmosphere's fixed temperature lapse rate; actual pressure altitude readouts from an altimeter use this same formula."
    ],
    "constants": [
      {
        "name": "standard_sea_level_pressure_hpa",
        "value": 1013.25,
        "unit": "hPa",
        "source": 0
      },
      {
        "name": "isa_exponent",
        "value": 0.190284,
        "unit": "dimensionless",
        "source": 0
      },
      {
        "name": "isa_feet_constant",
        "value": 145366.45,
        "unit": "feet",
        "source": 0
      }
    ],
    "examples": [
      {
        "name": "worked example",
        "inputs": {
          "station_pressure_hpa": 1013.25
        },
        "expected": {
          "answer": "0.00 ft"
        },
        "check": "At exactly the ICAO standard sea-level pressure, the ratio P/1013.25 is 1, 1^0.190284=1, so (1-1)*145366.45=0 by direct arithmetic; pressure altitude at standard sea-level pressure is 0 feet by definition."
      },
      {
        "name": "test vector: lower pressure",
        "inputs": {
          "station_pressure_hpa": 950
        },
        "expected": {
          "answer": "1772.03 ft"
        },
        "check": "By hand: ratio=950/1013.25=0.937561; ln(0.937561)=-0.064476; *0.190284=-0.012268; e^-0.012268=0.98781; 1-0.98781=0.01219; *145366.45=1772.0. Cross-checked against the common aviation rule of thumb of about 27 to 30 feet per hPa below standard, (1013.25-950)*27=1708, which is the right order of magnitude."
      }
    ],
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    "deck_category": "other"
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  "kind": "method",
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          "value": "ICAO Doc 7488, Manual of the ICAO Standard Atmosphere.",
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        "added_utc": "2026-09-30T22:39:30.722Z",
        "added_by": "method:Pressure altitude from station pressure (ISA)",
        "why": "the method that computed this answer",
        "check": null,
        "status_label": "pending",
        "signature": null
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  }
}