{
  "id": "pitot-static-climb",
  "version": 1,
  "title": "The airspeed that would not settle",
  "aircraft": { "id": "cherokee-180", "name": "Piper Cherokee 180", "atlas": "/atlas" },
  "synthetic": "Synthetic case. The symptoms were authored for this exercise from the published behaviour of the Cherokee 180's pitot-static system (the Aircraft Atlas pack and its sources). They are not a report from any flight, and the airplane is the Atlas's Cherokee 180, not a specific aircraft.",
  "briefing": [
    "Configuration assumed for this case, stated because the airplane in the Atlas is a type, not an individual: the pitot mast under the left wing carries both the ram opening and the static hole (the pack's static-port entry), and an alternate static source valve is fitted below the panel. The family service manual describes that valve as standard; the 1973 handbook does not mention it, so the case names the assumption instead of hiding it.",
    "Setting: a cool spring morning after a night of rain. The airplane was tied down outside without its pitot cover. Surface temperature 4 °C; the briefing for this scenario puts the freezing level near 3,000 ft.",
    "Timeline: a normal run-up and take-off. The airspeed indicator read normally on the roll and in the initial climb. Passing about 3,500 ft in a cruise climb, the indication stops making sense."
  ],
  "symptoms": [
    "The airspeed indication no longer matches the attitude and power you are holding.",
    "The airplane flies normally: the controls feel as they should for a climb at this power setting.",
    "Engine instruments are normal and the ammeter shows a normal charge."
  ],
  "truth": "pitot-and-drain-blocked",
  "causes": [
    {
      "id": "pitot-ram-blocked",
      "name": "Pitot ram opening blocked, drain clear",
      "summary": "Debris in the mast's front opening while the drain hole underneath stays open, so the pitot line vents to ambient pressure.",
      "system": "pitot-static",
      "components": ["pitot-mast", "airspeed-indicator"]
    },
    {
      "id": "pitot-and-drain-blocked",
      "name": "Pitot opening and drain both blocked",
      "summary": "Water from the overnight rain froze inside the mast as the climb passed the freezing level, sealing the ram opening and the drain, so the pitot line holds whatever pressure it had at that moment.",
      "system": "pitot-static",
      "components": ["pitot-mast", "pitot-static-lines", "airspeed-indicator"]
    },
    {
      "id": "static-blocked",
      "name": "Static hole blocked",
      "summary": "The small static hole on the underside of the mast is sealed, so the altimeter, the vertical speed indicator and the airspeed indicator all see a trapped static pressure.",
      "system": "pitot-static",
      "components": ["static-port", "altimeter", "vertical-speed-indicator", "airspeed-indicator", "alternate-static"]
    },
    {
      "id": "water-in-pitot-line",
      "name": "Water in the pitot line",
      "summary": "Liquid water moving in the pitot line between the mast and the panel, the classic cause of an erratic airspeed indication in the service manual's troubleshooting table.",
      "system": "pitot-static",
      "components": ["pitot-static-lines", "airspeed-indicator"]
    }
  ],
  "observations": [
    {
      "id": "asi-level",
      "label": "Level off at cruise power and read the airspeed indicator",
      "phase": "flight",
      "values": { "pitot-ram-blocked": "zero", "pitot-and-drain-blocked": "steady-odd", "static-blocked": "steady-odd", "water-in-pitot-line": "erratic" },
      "options": {
        "zero": "The needle sits on zero and stays there.",
        "steady-odd": "A steady needle, but not the number this power setting and attitude should give.",
        "erratic": "The needle wanders several knots either way and never settles."
      },
      "components": ["airspeed-indicator"]
    },
    {
      "id": "asi-trend",
      "label": "Hold a steady climb attitude and power for 500 ft and watch the airspeed",
      "phase": "flight",
      "values": { "pitot-ram-blocked": "stays-zero", "pitot-and-drain-blocked": "rises", "static-blocked": "falls", "water-in-pitot-line": "wanders" },
      "options": {
        "stays-zero": "Zero all the way up.",
        "rises": "It rises steadily through the climb, although attitude and power have not changed.",
        "falls": "It falls steadily as you climb.",
        "wanders": "It keeps jumping around with no trend either way."
      },
      "components": ["airspeed-indicator", "pitot-mast"]
    },
    {
      "id": "alt-vsi",
      "label": "Cross-check the altimeter and the vertical speed indicator",
      "phase": "flight",
      "values": { "pitot-ram-blocked": "normal", "pitot-and-drain-blocked": "normal", "static-blocked": "frozen", "water-in-pitot-line": "normal" },
      "options": {
        "normal": "Both behave: the altimeter winds up through the climb and the VSI shows about 500 ft per minute.",
        "frozen": "The altimeter has stopped near 3,400 ft and the VSI reads zero, although the nose is up and the power is set for a climb."
      },
      "components": ["altimeter", "vertical-speed-indicator", "static-port"]
    },
    {
      "id": "alt-static",
      "label": "Open the alternate static source and watch all three instruments",
      "phase": "flight",
      "values": { "pitot-ram-blocked": "blip", "pitot-and-drain-blocked": "blip", "static-blocked": "recover", "water-in-pitot-line": "blip" },
      "options": {
        "blip": "The altimeter and the airspeed step up a little and the VSI shows a brief climb; then the airspeed behaves exactly as it did before.",
        "recover": "The altimeter jumps and starts winding up again, the VSI shows a brief climb and then a normal rate, and the airspeed comes back to a sensible number, reading a little high."
      },
      "components": ["alternate-static", "static-port"]
    },
    {
      "id": "ground-mast",
      "label": "After landing: look at the mast on the ramp",
      "phase": "ground",
      "values": { "pitot-ram-blocked": "debris", "pitot-and-drain-blocked": "water-drips", "static-blocked": "water-static", "water-in-pitot-line": "water-drips" },
      "options": {
        "debris": "Something is packed into the ram opening; the drain hole and the static hole underneath are clear.",
        "water-drips": "Water drips from the drain hole when you tap the mast. The ram opening and the static hole look clear now; any ice there has long since melted.",
        "water-static": "A bead of water sits over the static hole on the underside; the ram opening and the drain are clear."
      },
      "components": ["pitot-mast", "static-port"]
    }
  ],
  "components": [
    {
      "id": "pitot-mast", "system": "pitot-static", "name": "Pitot mast",
      "note": "A blade-style mast under the left wing. Ram air enters the front opening and is piped through the wing to the airspeed indicator. The mast has a drain hole for moisture and takes a cover when parked. Blocked with the drain clear, the airspeed reads zero; blocked with the drain also blocked, the airspeed freezes and then behaves like an altimeter.",
      "sources": ["Piper Service Manual 753-586, Section X, Pitot-Static System", "Cherokee 180 Owner's Handbook (1973), Preflight", "PHAK 25C, Chapter 8, Blocked Pitot System"]
    },
    {
      "id": "static-port", "system": "pitot-static", "name": "Static port",
      "note": "On the -180 the static source is a small hole on the underside of the pitot mast itself, not a separate port on the fuselage, so an obstruction there can disturb both pressures. A blocked static source freezes the altimeter, zeroes the VSI and makes the airspeed read low above the blockage altitude and high below it.",
      "sources": ["Piper Service Manual 753-586, Section X, Pitot-Static System", "PHAK 25C, Chapter 8, Blocked Static System"]
    },
    {
      "id": "pitot-static-lines", "system": "pitot-static", "name": "Pitot and static lines",
      "note": "Two small lines run from the mast through the wing and cabin sidewall to the instruments: pitot pressure to the airspeed indicator only, static pressure to all three. Water in the lines is a classic cause of erratic airspeed indications, which is why the mast has a drain and why maintenance leak-checks the system.",
      "sources": ["Piper Service Manual 753-586, Section X, Troubleshooting", "PHAK 25C, Chapter 8"]
    },
    {
      "id": "alternate-static", "system": "pitot-static", "name": "Alternate static source",
      "note": "A valve below the panel that lets the instruments sense cabin pressure if the outside static source is blocked. Cabin pressure is slightly lower than outside, so with the alternate source open the altimeter and airspeed read a little high and the VSI shows a brief climb. Described as standard in the family service manual; the 1973 handbook does not mention it, which is why this case states it as an assumption.",
      "sources": ["Piper Service Manual 753-586, Section X, Alternate Static Source", "PHAK 25C, Chapter 8, Alternate Static Source"]
    },
    {
      "id": "pitot-heat", "system": "pitot-static", "name": "Pitot heat",
      "note": "An optional electric heating element inside the mast, with a cockpit switch and its own circuit breaker, which keeps ice from closing the pitot opening in visible moisture. Optional equipment, so this case does not assume it is fitted; and the sources read for the Atlas say nothing about how quickly it clears ice already formed, so the case offers no observation built on it.",
      "sources": ["Piper Service Manual 753-586, Section X", "Cherokee 180 Owner's Handbook (1973), Electrical System"]
    },
    {
      "id": "airspeed-indicator", "system": "pitot-static", "name": "Airspeed indicator",
      "note": "The only instrument that uses pitot pressure: a diaphragm measures the difference between pitot pressure and static pressure. Because it compares two pressures, both a pitot blockage and a static blockage affect it, in different ways.",
      "sources": ["PHAK 25C, Chapter 8, Airspeed Indicator"]
    },
    {
      "id": "altimeter", "system": "pitot-static", "name": "Altimeter",
      "note": "A stack of sealed aneroid wafers that expand as static pressure falls. Static-only: it freezes at the altitude where a static blockage began.",
      "sources": ["PHAK 25C, Chapter 8, Altimeter"]
    },
    {
      "id": "vertical-speed-indicator", "system": "pitot-static", "name": "Vertical speed indicator",
      "note": "A diaphragm inside a case that leaks through a calibrated orifice, which is why it lags by several seconds. Static-only: with a blocked static source it reads zero no matter what the airplane does.",
      "sources": ["PHAK 25C, Chapter 8, Vertical Speed Indicator"]
    }
  ],
  "debrief": {
    "pitot-and-drain-blocked": "With the ram opening and the drain both sealed, the pressure in the pitot line is trapped at whatever it was when the ice formed. The airspeed indicator compares that trapped pressure with static pressure, which keeps falling as the airplane climbs, so the needle rises in a climb and would fall in a descent: the airspeed indicator has turned into a second altimeter. The altimeter and the VSI, which use only the static hole, are untouched, and the alternate static source changes nothing that matters. The teaching point from the handbook: a plausible, steady airspeed can still be wrong, and the cross-check is what exposes it.",
    "pitot-ram-blocked": "A blocked ram opening with a clear drain lets the pitot line vent to ambient pressure, so the airspeed indicator, which reads pitot minus static, falls to zero and stays there whatever the airplane does. That is a different signature from a trapped pressure: zero, not a plausible number that tracks altitude.",
    "static-blocked": "A sealed static hole traps static pressure for all three instruments: the altimeter freezes, the VSI reads zero, and the airspeed reads low above the blockage altitude because the trapped static pressure is higher than the real one. The alternate static source is the equipment the airplane carries for exactly this: with cabin pressure on the static side, the altimeter and the VSI come back, reading slightly high.",
    "water-in-pitot-line": "Water moving in the pitot line gives an airspeed that will not settle, jumping either way with no trend, while the altimeter and the VSI are untouched. The service manual's troubleshooting table lists it among the causes of erratic airspeed indications, and the mast's drain exists to keep it out."
  },
  "sources": [
    { "id": "piper-sm", "title": "Piper Cherokee Service Manual 753-586, Section X (Instruments): Pitot-Static System, Alternate Static Source, Troubleshooting", "locator": "Reissued January 15, 1981, with revisions through January 31, 2008. Used for system description only; no maintenance procedure is reproduced.", "url": "https://www.touringmachine.com/Cherokee/PDFs/Piper%20753-586%20MX%20PA-28-140,150,160,180,235,R180,R200.v2008.pdf" },
    { "id": "phak-25c", "title": "Pilot's Handbook of Aeronautical Knowledge, FAA-H-8083-25C, Chapter 8 (Flight Instruments): Blocked Pitot System, Blocked Static System, Alternate Static Source, Airspeed Indicator, Altimeter, Vertical Speed Indicator", "locator": "2023 edition (incorporating Addendum C, March 2023)", "url": "https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/faa-h-8083-25c.pdf" },
    { "id": "poh-1973", "title": "Cherokee 180 PA-28-180 Owner's Handbook, Part No. 761 513: Preflight; Electrical System", "locator": "Issued June 1972, revised January 1973. An Owner's Handbook is not the FAA-approved Airplane Flight Manual; facts are summarised, not reproduced.", "url": "https://takeflightsandiego.com/assets/documents/1973%20PA-28-180.pdf" },
    { "id": "atlas-pack", "title": "Aircraft Atlas, Piper Cherokee 180 pack: pitot-static system, its eight components, the pitot-static tour and its challenges", "locator": "The published configuration this case is built on; every component note above is that pack's entry, paraphrased.", "url": "/atlas?system=pitot-static" }
  ]
}