Pressure Altitude / Density Altitude mechanism

Model scope

The formulas are recognizable aviation approximations and the non-certified-for-flight-planning label is appropriate. The instrument needs explicit input units, an explicit definition that ISA temperature is evaluated at pressure altitude, and a defined ISA lapse-rate/table and valid operating range before release.

• The pressure-altitude formula is an aviation approximation using 1000 ft per inHg; it is not the exact standard-atmosphere pressure-altitude equation, especially for large altimeter-setting deviations.
• Density altitude requires ISA temperature at the pressure altitude, but the specification does not explicitly state that ISA_temp must be evaluated at PA.
• The ISA temperature source, lapse rate, altitude range, and interpolation method are not defined; the stated data need is insufficient as an implementation specification.

Units and conventions

• field_elev and all altitude outputs are in ft.
• altimeter is in inches of mercury (inHg); if supplied in hPa, it must first be converted, approximately hPa / 33.8639.
• OAT and ISA_temp are in degrees Celsius.
• The coefficient 120 has units of ft per degree Celsius.
• For the test vectors, ISA temperature is approximated as ISA_temp = 15 - 1.98*(PA/1000), in degrees Celsius, within the troposphere.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "field_elevation_ft": 0,
    "altimeter_setting_inHg": 29.92,
    "OAT_C": 15
  },
  "expected_outputs": {
    "pressure_altitude_ft": 0,
    "density_altitude_ft": 0
  },
  "working": "PA = 0 + (29.92 - 29.92)*1000 = 0 + 0 = 0 ft.\nISA_temp = 15 - 1.98*(0/1000) = 15.0 C.\nDA = 0 + 120*(15.0 - 15.0) = 0 + 120*0 = 0 ft."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

The extreme-magnitude vector produces Infinity for both outputs in plain JavaScript arithmetic. The instrument should reject or flag such inputs rather than expose non-finite altitudes. The supplied specification has no actual denominator-based undefined-result trap and no explicitly defined multi-regime formula branch.

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche4/tranche4-results.json
• BOUNDARY_HAZARD_CATALOG.json