Passenger Boarding Stairs Product

Overview

Passenger boarding stairs (PBX) are the simplest form of aircraft boarding equipment: a mobile stairway that rolls up to the aircraft, lifts its top platform to align with the cabin door, and provides direct passenger access. Unlike jet bridges, which are fixed to the building and telescope to the aircraft, boarding stairs are fully mobile and completely independent — they require no gate equipment and can serve any aircraft at any remote stand.

The design is mechanically straightforward: a vertical lift system raises and lowers the flight and platform, hydraulic brakes hold the stairs stationary, and proportional control allows the operator to approach the aircraft gently and position the top of the stairs to within ±50 mm of the sill. The tradeoff is weather exposure — passengers walk outside briefly between the stairs and the terminal, and loading and unloading happens in sequence rather than simultaneously.

Mechanics

The Stair Flight is a rigid frame carrying 10–15 aluminum Stair Tread steps mounted on Stringer Beam beams. The treads have perforations or grating to shed water, and each edge is guarded by a Nose Guard to prevent trips.

At the top of the flight is the Top Platform, a raised landing ~2.5 m wide that aligns with the aircraft cabin door sill. The platform frame is anchored to the top of the stringers, and its Platform Floor is grated aluminum. Two Door Roller wheels ride against the aircraft fuselage during final approach, centering the stairs at the door.

The entire assembly is suspended on four Lift Cylinder hydraulic rams mounted between the Mobile Chassis frame and the flight. A pair of Parallel Linkage pantograph arms maintain level tread angle as the cylinders extend, so passengers always walk on a horizontal surface regardless of height. A Height Sensor potentiometer feeds back the platform height to the control system.

Mobility and positioning

The Mobile Chassis is a welded steel box frame rolling on four pneumatic Guide Wheel casters. The Drive Bogie provides self-propulsion: a Drive Motor (electric AC induction ~15 kW) drives the Transmission gearbox down to ~0.5 km/h wheel speed, giving precise control during the approach to the aircraft. The Steering Arm allows the operator to steer manually or via power-assist.

As the nose of the stairs approaches the aircraft fuselage, a Aircraft Bumper elastomer pad contacts the skin and gently stops the advance. The Wheel Lock spring-applied hydraulic brakes then engage, holding the stairs in place. If hydraulic pressure is lost, the springs mechanically apply the brakes — a critical safety feature preventing drift toward the aircraft.

Height and alignment

The operator commands the Vertical Lift System through a Operator Console proportional joystick. The Lift Valve proportional directional control meter flows to all four cylinders simultaneously, raising the platform smoothly at ~0.2 m/s. The Parallel Linkage mechanism ensures the Stair Flight stays level during height changes.

Once the platform approaches the aircraft door sill (e.g., 3.81 m for a B737 main deck), the operator fine-tunes the final height — targeting within ±50 mm — using the proportional control. A Limit Switch at maximum and minimum height prevents overtravel, and a LCD Panel display in the operator cabin shows the current height in real time.

The Safety Relay hardwired interlock prevents any lift or drive motion if the Parallel Linkage becomes unbalanced or if a Pressure Sensor detects load imbalance on any cylinder — a sign of uneven contact or structural misalignment.

Handrails and safety

The Handrail Assembly are paired stainless-steel tubes running both sides of the flight, mounted via Rail Bracket to the Stringer Beam beams. Each rail is ~40 mm diameter, allowing comfortable one-hand grip. The top Side Rail curves around to the Top Platform corners, where it terminates in a Rail End Cap hemisphere preventing clothing snags.

Safety features include non-slip Stair Tread surfaces (perforated aluminum or coated with elastomer), adequate handrail height and grab length, and the fact that stairs are narrow and compact — a passenger who falls rolls down the flight rather than off the side.

Hydraulics and power

The Hydraulic System system is modest compared to a jet bridge: a Hydraulic Pump (typically 50–100 L/min, 100–160 bar) fed from the Drive Motor. The Hydraulic Tank includes a cooler to reject heat during continuous operation. The Lift Valve proportional directional-control directs flow to raise or lower the cylinders, and a Brake Valve pilot-operated check valve holds the cylinders locked when the operator releases the joystick, preventing creep.

Typical operation: approach the aircraft at walking pace, dock the bumper, engage brakes, raise the stairs to height over 2–3 minutes, allow boarding/deplaning, lower the stairs, release brakes, reverse away. Cycle time is ~10–15 minutes per aircraft.

Deployment and integration

Boarding stairs are deployed at remote stands (no gate infrastructure) and at medium-sized airports where boarding bridges are too capital-intensive. They are standard equipment at most regional airports and are used globally under EN 1760 equipment certification. Modern designs feature proportional hydraulic control for smooth motion and electric drive for quiet operation in congested gate areas.