Application Guide

63-706245
Aircraft Passenger Jetty Loading (See Fig. 54)
Ultrasonic Detector Motor/Gearbox Inverter
Control Power
Skirt
In/Out
P/Down
Fig. 54. Aircraft passenger jetty loading application.
Application Description
With the existing control system the jetty is started by hand and the operator drives the jetty out towards the aircraft. As the
flexible skirt on the extremity of the jetty approaches the side of the fuselage, the operator stops the jetty and then slowly
inches the jetty into its final docking position, where limit switches disable the control circuit and the motor powers down.
Occasionally, the operator makes a mistake and the jetty skirt is driven into the fuselage at full speed. There is sufficient inertia
in the equipment to damage the fuselage of the aircraft.
Fitting the VFD to the existing jetty motor allows smooth and progressive acceleration/deceleration with precise control even at
low speeds. In addition an ultrasonic sensor is required to detect the proximity of the aircraft. Several control modifications are
designed to prevent these accidents without loss of functionality and speed.
On start-up from a full retracted position, the VFD accelerates the jetty drive motor up to full speed within 4-6 seconds and the
jetty extends as normal. As the jetty approaches the aircraft the ultrasonic sensor detects the proximity of the fuselage and
signals the VFD to reduce speed (within 2-3 seconds) by 75 to 80% for the final docking phase.
The existing limit switches still operate and stop the jetty. This slower docking speed reduces the likelihood of damage to the
fuselage. The reduction in human control also reduces the chance of accidents. The jetty control circuit is not disabled when
retracting from the aircraft, as under some circumstances it is paramount to remove the jetty from the aircraft as quickly as
possible.
Fit the VFD into the electrical circuits before the existing contractors. The VFD is then interfaced with these contactors to
provide the normal start/stop functions, whilst retaining the existing limits and emergency control. Install the ultrasonic detector
at a suitable angle to be able to detect all types of aircraft. It may be necessary to install a second detector to guarantee
reliability. To enhance reliability the sensors should be mounted in a heated weatherproof box to prevent rain and frost affecting
performance.
Other Applications
— Benefits.
— Reduction in potential damage to fuselage.
— Smooth acceleration/deceleration.
— Precise positioning.
— Shock free starting and stopping.
— Semi-automatic docking.