Overview
ISO 7717:1985 specifies the performance requirement factors for design of four-wheel-drive aircraft tow tractors. It does not prescribe a full set of design criteria but identifies and summarizes the parameters design and specifying engineers must evaluate when establishing performance requirements. The standard covers aircraft and airport characteristics, tow‑vehicle general features, weight and traction, powertrain and braking considerations, and tabulated design data with explanatory examples.
Key topics and technical requirements
- Scope: Factors to be considered in setting tow‑tractor performance requirements (aircraft, airport, and tow‑vehicle characteristics).
- Aircraft characteristics: dimensions, landing‑gear/wheel count, tow‑attach point, gross/empty weight and weight distribution, breakaway resistance, rolling resistance, turn radius and towbar angular limits.
- Airport environment: maximum grades, taxiway/runway crossing speeds, parking layouts, pavement strength, bridge/overpass clearances, approach/breakover angles, expected towing routes and distances.
- Tow‑vehicle characteristics: dimensional limits, operator visibility/position, steering options (coordinated/crab), wheels and tyres, braking capability, powertrain, maintenance access, electrical power for aircraft systems, communications and lighting.
- Weight & traction: required tractor weight to develop drawbar pull; methods to increase traction (ballasting, limited‑slip differentials, chains/studded tyres, sanding).
- Performance factors & definitions: clear definitions and typical values for breakaway resistance (BR), rolling resistance (RR ≈ 1–2% straight pull, commonly 2%), grade resistance (≈1% per 1% grade), acceleration resistance (AR), engine thrust (ET, e.g., engine idle thrust during push‑out), rim pull, tractive effort (TE = μ × tractor weight), and drawbar pull.
- Power & braking: guidance on engine/rim‑pull requirements, mechanical vs electric drive efficiencies, brake sizing and deceleration limits to avoid towbar/airframe shock.
Practical applications and users
ISO 7717:1985 is intended for:
- Design and specifying engineers developing tow tractors or specifying performance targets for ground support equipment (GSE).
- GSE manufacturers sizing powertrains, braking systems, and traction solutions for four‑wheel‑drive aircraft tractors.
- Airlines, ground handlers and airport planners evaluating compatibility with aircraft types, apron layouts, pavement strength and towing procedures.
- Regulatory bodies and maintenance teams for establishing safe operating envelopes and serviceability requirements.
Practical uses include calculating required drawbar pull and tractor weight for specific aircraft and airport conditions, selecting tyres/ballast or traction aids for icy ramps, and sizing engine power and braking capacity to minimize impact loads during push/pull operations.
Related guidance
- Prepared by ISO/TC 20 (Aircraft and space vehicles). For full design integration, consult this standard alongside other ISO and industry documents covering aircraft towing attachments and ground support equipment safety.
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