Overview
ISO 1151-5:1987, "Flight dynamics - Concepts, quantities and symbols - Part 5: Quantities used in measurements," standardizes the physical quantities, symbols and measurement-related definitions used in airborne flight testing and instrumentation. It focuses on quantities needed to describe the atmosphere, geometric and geopotential altitudes, equivalent altitudes referenced to a Standard Atmosphere, motion-related physical quantities (pressures, temperatures, densities), speeds and indicated Mach number, on‑board accelerometer indications, and terms for pressure differences used in some countries.
Key topics
- Fundamental atmospheric quantities: definitions for air pressure, temperature, density and relative density as used in flight measurements.
- Altitudes: geometric vs. geopotential altitude and equivalent altitudes-pressure altitude, temperature altitude, density altitude-defined with respect to a Standard Atmosphere (see ISO 2533).
- Motion-related quantities: static and total (pitot) pressure, total temperature, kinetic pressure and on‑board probe input values.
- Speeds and Mach: clear definitions and computation relationships for calibrated airspeed, indicated airspeed, equivalent airspeed and indicated Mach number (including the formulas and conventions used to calculate them from pitot/static inputs).
- On‑board accelerometer indications: how accelerometer outputs relate to gravitational and inertial accelerations, sensor axes and mounting effects.
- Measurement errors and probe corrections: classification of aerodynamic and instrumentation errors; definition of probe input quantities and correction coefficients used to account for installation and flow effects.
- Terminology table: country-specific terms for pressure differences (useful for international test programs).
Applications and users
ISO 1151-5 is practical for professionals involved in:
- Flight-test engineering and data analysis (airspeed/Mach calibration, altitude conversions)
- Avionics and sensor manufacturers (pitot/static systems, temperature probes, accelerometers)
- Aircraft performance and aerodynamicists (density altitude, kinetic pressure, probe correction)
- Certification authorities and standards bodies (harmonizing measurement definitions across programs)
- Aerospace researchers and instrumentation engineers who need consistent symbols and definitions for publication and data exchange
Practical benefits include consistent terminology across international projects, standardized computation methods for airspeed and Mach, and clearer guidance for correcting sensor installation errors.
Related standards
- ISO 2533 - Standard atmosphere (referenced for equivalent altitudes and standard atmosphere parameters)
- Other parts of ISO 1151 - provide complementary definitions for aircraft motion, stability, geometry and flight envelopes
Keywords: ISO 1151-5, flight dynamics, quantities used in measurements, calibrated airspeed, indicated Mach number, pitot-static, density altitude, accelerometer indications, ISO 2533.
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