Overview
ISO 6702-1:1991 - Aircraft - Requirements for on-board weight and balance systems - Part 1: General - defines the functional, performance and installation requirements for on-board weight and balance systems (OBWBS) intended for civil transport aircraft. This first-edition document replaces ISO 6702:1984 and establishes classes of systems, minimum performance levels, environmental and maintainability expectations, and optional capabilities such as in-flight weight estimation and remote displays.
Key topics and technical requirements
- System classes and confidence levels
- Class I: very high accuracy and confidence (intended to measure and display aircraft weight and centre of gravity).
- Class II: high confidence, lower accuracy than Class I (weight and balance displayed).
- Class III: high confidence, displays only balance condition.
- Target overall level of confidence: 99.7% for Class I, 95% for Class II/III.
- Accuracy & performance
- Class I accuracy objective: ±1% of actual weight and ±1% of reference chord (MAC) for centre of gravity, aimed to be guaranteed within three standard deviations.
- Response time: display weight and CG within 1 minute of initial self-test.
- Operational weight range: from 10% below tare weight to 15% above maximum gross weight (overflow indication required).
- System architecture
- Core subsystems: display unit, computer unit, calibration unit, sensors (may be duplicated).
- Computer unit weight objective: ≤ 22.7 kg (excluding cabling).
- Power: operate from aircraft electrical power (115 V AC, 400 Hz) and from ground power without interruption.
- Interfaces: provisions for ARINC 429 outputs and compatibility with flight data/monitoring systems.
- Environmental, reliability and maintainability
- Environmental requirements reference ISO 7137 (temperature, altitude, humidity categories).
- Calibration interval objective: not required more frequently than 10 000 flight hours equivalent.
- Designed for easy component replacement without recalibration; self-test and malfunction diagnostics required.
- Optional functions
- In-flight weight & CG estimation (using fuel, fuel transfer, navigation inputs).
- Fuel usage planning, remote displays, tail-tip alarm, degraded-mode operation.
Applications and users
ISO 6702-1:1991 is used by:
- Aircraft manufacturers and design engineers specifying OBWBS architecture and installation.
- Avionics and sensor suppliers developing aircraft weight/balance equipment.
- Airlines and integrators assessing on-board systems for operational safety and dispatch.
- Certification authorities and flight-test teams verifying compliance with weight-and-balance requirements.
- Maintenance and reliability engineers implementing calibration, troubleshooting and replacement procedures.
Related standards
- ISO 6702-2 (Design, Performance and Interface characteristics)
- ISO 7137 (Environmental conditions and test procedures for airborne equipment)
- ARINC 429 and ARINC 737 references; EUROCAE ED-14B / RTCA DO-160B referenced for environmental endorsement
Keywords: ISO 6702-1:1991, on-board weight and balance systems, OBWBS, aircraft weight and balance, centre of gravity, ARINC 429, ISO 7137, aircraft certification.