ISO 5129:2001

Overview

ISO 5129:2001 - "Acoustics - Measurement of sound pressure levels in the interior of aircraft during flight" - specifies instruments, test procedures and reporting requirements for measuring sound pressure levels at crew and passenger locations in aircraft under steady flight. The standard covers a complete electroacoustic measurement chain (microphone to readout), preferred analysis in one‑third‑octave bands, and procedures to ensure reproducible results and quantifiable measurement uncertainty.

Key topics and technical requirements

• Scope & purpose: Measurement and reporting of interior aircraft acoustics to describe the onboard acoustical environment and to provide a basis for uncertainty estimates.
• Measurement system: Complete systems must meet applicable class 2 performance specifications (IEC 61672‑1) from microphone through readout. One‑third‑octave analysis requires spectrum analysers conforming to IEC 61260 class 2.
• Microphone system: Random‑incidence microphone systems verified per IEC 61183; windscreen insertion loss must be known; mounting and orientation specified to minimize shielding.
• Sound calibrator: Conform to IEC 60942 (class 1C); nominal calibration tone between 200 Hz and 1 250 Hz; pre‑ and post‑test calibration checks required.
• Measurement locations & mounting:
  • Passenger head position: microphone on seat centreline, axis vertical, 0.15 m ±0.025 m from headrest and 0.65 m ±0.05 m above seat cushion.
  • Crew stations: microphone within 0.1 m of typical ear position; standing cabin crew at 1.65 m ±0.1 m above floor.
  • Crew sleeping quarters: 0.15 m ±0.025 m above mattress/headrest; at least 0.15 m from nearby walls.
• Recording & averaging:
  • Minimum recording duration: 30 s per measurement.
  • Averaging time for one‑third‑octave levels: minimum 16 s (or include specified beat periods if present).
  • If beats occur, recordings must include multiple beat periods (minimums specified).
• Test conditions: Aircraft fully furnished; environmental control systems operating normally (or at design airflow); minimal cabin transients unless transients are under test.
• Flight and metadata: Record altitude, Mach number/airspeed, engine/rotor speeds or power settings, fuel state, cabin pressure/temperature, centre‑of‑gravity, and environmental control settings.
• Verification: Instrument performance should be verified within one year of testing; background electrical noise and system sensitivity checks required.
• Data quality: Annex A provides guidance on measurement uncertainty.

Applications and who uses it

• Aircraft manufacturers and acoustics engineers: interior noise characterization during design and certification.
• Cabin systems and HVAC designers: verify noise from environmental control and ventilation.
• Airline operators and maintenance teams: diagnose and monitor cabin noise sources.
• Certification authorities and regulatory bodies: harmonized test methods for regulatory compliance and passenger comfort assessments.
• Acoustics consultants and testing laboratories: in‑flight noise surveys, validation of mitigation strategies, and acoustic reporting.

Related standards

Normative references in ISO 5129 include:

• IEC 61672‑1 (sound level meter specifications)
• IEC 61260 (octave and fractional‑octave filters)
• IEC 61183 (random‑incidence/diffuse‑field calibration)
• IEC 60942 (sound calibrators)
• ISO 31‑7 / ISO/IEC 80000‑8 (quantities and units - acoustics)

Keywords: ISO 5129, aircraft interior acoustics, sound pressure levels, one‑third‑octave band, microphone system, sound calibrator, measurement uncertainty, steady flight, IEC 61672.