ISO 9662:1994

Overview

ISO 9662:1994 specifies environmental and operating humidity, temperature and pressure tests for airborne equipment. Intended primarily for civil and transport aircraft, the standard defines test requirements and procedures to evaluate susceptibility of aerospace equipment to moisture ingress, frosting and condensation that occur during flight transitions through high-humidity atmospheres combined with changing temperature and pressure.

Key topics and requirements

• Scope: Applies to airborne equipment that may experience external/internal condensation, icing or moisture penetration during descent from high-altitude cold to warmer humid air. Not intended for prolonged ground humidity exposure (see ISO 7137 for tropical conditions).
• Three prescribed tests:
  • Test 1: Rapid temperature/pressure cycling with induced moisture - includes phases to cool to low temperature, introduce humidity, reduce pressure to simulate altitude, then rewarm to +30 °C ±2 °C and maintain relative humidity 95–100%. Functional operation and visual inspection for water ingress are required.
  • Test 2: Repeated multi-cycle test (four cycles total) for equipment where cumulative condensation over several descents is critical. Follows similar phase structure to Test 1; options exist for cycle timing (e.g., 24 h cycles or continuous sequencing).
  • Test 3: For open-construction elements where pressure change is not influential. Two methods-Method A (two chambers) and Method B (single chamber)-simulate freezing, melting/condensation and moisture penetration. Method B ramps temperature from low to +30 °C over 1–2 h with relative humidity near saturation.
• Common parameters:
  • Low-temperature condition example: −20 °C ±2 °C (or as specified by equipment requirements).
  • Temperature gradients limited to ≤ 3 °C/min during transitions.
  • Pressure change to simulate descent must be achieved in about 15 minutes.
  • Functional tests are required during/after sequences and visual inspections for water penetration.

Applications and users

ISO 9662 is used for:

• Qualification and verification of avionics, sensors, actuators and other airborne equipment vulnerable to condensation.
• Design validation for enclosure sealing, thermal pathways and moisture mitigation.
• Test houses and aerospace environmental test labs, manufacturers, integrators and certification authorities evaluating equipment performance under moisture and thermal/pressure transients.

Benefits include improved reliability in service, clearer acceptance criteria for moisture-related failures, and guidance for test planning and facilities.

Related standards

• ISO 7137:1992 - environmental and test procedures for airborne equipment (covers prolonged humidity/tropical conditions).
• ISO 9662 is aligned with aerospace environmental test practices and complements standards such as EUROCAE/ED-14C and RTCA/DO-160 (see ISO 7137 references).