Overview
ISO 268:1980 - Aircraft - Mechanical and electromechanical indicators - General requirements defines general characteristics and design requirements that apply to mechanical and electromechanical aircraft cockpit indicators. It is intended to be read together with individual instrument specifications. The standard treats an indicator as a unit primarily concerned with the visual display of information and requires manufacturers to declare finished indicator case size and type to facilitate installation.
Key topics and technical requirements
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Scope and integration
- General requirements apply to all mechanical and electromechanical flight-deck indicators and complement individual instrument specifications.
- Manufacturers must declare case dimensions and mounting restrictions to aid installation and vibration testing.
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Case, sealing and pressure
- Indicator housings must not degrade instrument performance when mounted as declared.
- Cases intended to be impermeable must meet water-impermeability tests (see ISO 2655) and hermeticity tests (IEC 68‑2‑17).
- Where required by the individual specification, cases must withstand external pressures (examples in the text: up to +100 kPa above internal pressure and down to −20 kPa below internal pressure) without unacceptable leakage or contact between needle and protective glass.
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Electrical connectors and grounding
- Multi-pin connectors must be designed to prevent incorrect mating; multiple connectors must avoid miswiring.
- Instrument cases with electrical connections must provide a grounding terminal/metalized point; internal low-voltage circuits (except internal lighting) should not route through case grounding.
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Readability, dials and pointers
- Dial design rules: graduations and numerals minimized to those needed for required reading accuracy; white markings on black backgrounds recommended; matte finishes.
- Circular scales increase clockwise; linear scales increase left-to-right or bottom-to-top.
- Pointer design: main pointer normally white; tip geometry to support rapid, unambiguous reading; avoid parallax and tunnel effects; limit stops to prevent pointer overtravel.
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Failure and anomaly signals
- Where possible a clear failure indication (flag, light or both) must obscure or replace unreliable indication. Signals must be rapidly detectable and automatically display if the signaling system fails.
- Numeric drum displays should be obscured if a failure is present.
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Protective glass and windows
- Protective glass/windows must resist +100 kPa differential pressure and be anti-reflective; plastics used under UV must not fluoresce.
Applications and who uses this standard
- Aircraft instrument manufacturers and component designers (mechanical and electromechanical indicators)
- Avionics and cockpit integrators specifying mounting, connectors and readability
- Maintenance engineers and installation technicians ensuring compliance with mounting, grounding and sealing requirements
- Certification authorities and test laboratories referencing general indicator requirements during approval and environmental testing
Related standards
- ISO 2655 - Environmental tests for aeronautical equipment (water impermeability)
- IEC 68‑2‑17 (CEI 68‑2‑17) - Environmental and mechanical robustness tests (hermeticity)
Keywords: ISO 268:1980, aircraft indicators, mechanical indicators, electromechanical indicators, avionics instrumentation, instrument case, dial readability, failure indication, hermeticity tests.