Source: https://guthlabs.ai/docs/instruments/airspeed-converter-ias-cas-tas-eas/mechanism/

instrument mechanism / verified-clean

# Airspeed Converter (IAS/CAS/TAS/EAS) mechanism

The inspectable method record for Airspeed Converter (IAS/CAS/TAS/EAS), kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The instrument should expose the exact atmosphere model, altitude units/reference, temperature-deviation convention, IAS/CAS error assumptions, and the precise compressible EAS definition before implementation. As written, the concept is plausible but mathematically underspecified, so the verdict is NEEDS_REVIEW.

- The specification does not define the IAS-to-CAS correction, so CAS cannot generally be computed from IAS without an instrument/position-error model; the vectors below explicitly assume IAS=CAS.

- TAS=CAS/sqrt(sigma) is only an incompressible or low-Mach approximation. For compressible flow, CAS must first be converted to impact pressure using the standard-sea-level isentropic relation, then local Mach number and TAS must be computed.

- The compressible correction is not stated mathematically. A standard model is qc/p=(1+(gamma-1)M^2/2)^(gamma/(gamma-1))-1, with CAS defined from qc at standard sea-level pressure.

- EAS is not explicitly defined. The vectors use EAS=TAS*sqrt(rho/rho0), equivalently EAS=sqrt(2q/rho0), which is the standard dynamic-pressure definition; this differs from CAS at appreciable Mach number.

- The ISA table, atmosphere-layer equations, altitude reference, and treatment of temperature deviation are unspecified.

## Units and conventions

- Altitude is geometric altitude in metres unless otherwise stated; one vector explicitly supplies 10000 ft converted to 3048 m.

- Airspeeds are knots indicated by the input and output labels; 1 kt=0.514444 m/s.

- Standard constants: gamma=1.4, R=287.05 J/(kg K), T0=288.15 K, p0=101325 Pa, rho0=1.225 kg/m^3.

- For the simplified vectors, pressure is the ISA pressure at altitude and actual temperature is T_ISA plus the stated temperature deviation; sigma=rho/rho0=(p/p0)/(T/T0).

- For the compressible vector, CAS is converted to impact pressure at standard sea level, then the same impact pressure is used at the local ISA static pressure. No position error, humidity, wind, or compressibility correction to the pitot instrument is included.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "input_type": "CAS",
    "CAS_kt": 100,
    "altitude_m": 0,
    "temperature_deviation_K": 0,
    "model": "incompressible approximation",
    "assumptions": "IAS=CAS; sigma=1"
  },
  "expected_outputs": {
    "CAS_kt": 100,
    "EAS_kt": 100,
    "TAS_kt": 100,
    "density_ratio_sigma": 1
  },
  "working": "At sea level, sigma=rho/rho0=1. EAS=TAS*sqrt(sigma)=100*sqrt(1)=100 kt. TAS=CAS/sqrt(sigma)=100/sqrt(1)=100 kt. Therefore CAS=100 kt, EAS=100 kt, TAS=100 kt."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

A temperature deviation of -288.15 K at sea level makes the absolute temperature exactly zero, causing the density denominator R*T to vanish. The converter should reject the input; any numeric output would be erroneous.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/airspeed-converter-ias-cas-tas-eas/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/airspeed-converter-ias-cas-tas-eas/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/airspeed-converter-ias-cas-tas-eas/qualification/>)

## Sources and evidence

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

- `VERIFIED_LEDGER.json`

- `evidence-tranche6/tranche6-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`