- Mockups covered by this specification are required for an early determination of the suitability of actual aircraft for service use. The mockup will provide a full size representation of the physical arrangement sufficient to permit checking compatibility with the handling, maintaining, loading and operating requirements for the aircraft and its equipment, particularly in regard to crew and passenger stations, cargo and weapons provision, equipment arrangments, propulsion system installations, vision, clearance, lighting, personnel safety, etc. Approval of a mockup enables the contractor to proceed with the design of the actual aircraft with reasonable assurance that the general arrangement and installations of equipment will be service accepted and will not be radically modified.