The ZT45TKT is designed for enplaning/deplaning passengers to/from an aircraft parked in the airport apron area. The stair assembly is mounted on a towable chassis and consists of a pivoted lower flight and a telescopic upper flight. The stair can be tilted and extended to achieve the best elevation in its working range. The unit has four hydraulically-operated vertical stabilizers to provide stability. Mechanical restraint devices are provided to prevent the stairs from lowering and retracting.