Building bridges: Andrea Medved of Dewbridge Engineering gives an overview of the basics of airbridge design. (Boarding Bridges).
Over four decades of boarding bridge history, various models have been put to the best use. Apron drive, radial drive, nose loader and over the wing, glass, or plain metal siding, today's PBBs are available in all shapes and sizes, appealing to individual buyers for the different advantages they offer.
An Apron Drive PBB is the traditional two- or three-tunnel bridge with simultaneous movement of outward (telescopic) and horizontal travel. It is the most popular with airport consultants as it is known for its flexibility in movement and can retract/extend from 30ft (9m) to 60ft (18m), depending on the specific model. This is ideal for use with multi-aircraft parking at one gate and at different positions. The Apron Drive PBB is designed for use with most jet aircraft, from regional jets to the wide-body Boeing -747, though its use with propeller aircraft is not recommended. Traditionally, Apron Drive PBBs required at least a 5ft (1.5m) pedestal base, limiting their use at regional airports. Recently Dewbridge Airport Systems in Ottawa, Canada, developed an Apron Drive model which can be installed directly to the concrete and which offers only a 12in (30cm) difference between the rotunda floor and the apron. This enables all grade level airports to use this flexible apron drive bridge for their jet aircraft. It should be noted that, as with all bridge models, the aircraft a bridge can service will directly depend on the terminal building height and on the length of the bridge and the apron slope.
The Radial Drive PBB has been around for a number of years, though only in the last five years has this style of bridge been brought back in vogue by Dewbridge Airport Systems, which has added features to make it the first PBB to cater to commuter and regional aircraft. Prior to this development, the configuration of today's commuter and regional aircraft prevented them from using the existing passenger boarding bridges. The advantage of the Regional Radial Drive PBB is that it is able to service propeller, commuter and regional aircraft as well as narrow-body jets up to the Boeing-757. The disadvantage is that although it has the traverse and lift capability of the apron drive, it has very limited telescopic motion. For applications where a propeller aircraft must be serviced, the radial PPB is the safest and most operator-friendly choice. Dewbridge, along with a few other manufacturers, offers this Radial Drive PBB as a grade level mountable product, in many cases, without the need for an expensive foundation other than existing concrete.
Nose Loader Bridges, or Pedestal Bridges, are PBBs with very limited movement. They are mounted to a fixed pedestal and will usually only telescope out a few feet to meet the aircraft door. Some models may have limited lateral motion in the cab, and vertical movement. These units are best suited to airports where the aircraft lead-in lines allow all aircraft passenger doors to end up in the same position, due to the bridge inflexibility. To offset this inflexibility, the Nose Loader has a minimum number of moving parts and is therefore relatively low in operational and maintenance costs as well as in initial investment. If the airport tail line limit is not a factor and the aircraft sizes not too varied, this is a popular choice. A very recent innovation is the `Over-the-Wing (OTW)' Bridge. As most of those involved in the aviation field know, airlines make money when planes fly, and not when they sit on the ground. The question was--how to get quicker turn-around times? Enter the OTW Bridge, which combines the traditional Apron, Radial or Nose Loader Bridge at the front with a cantilevered Radial Bridge that reaches over the left wing to the rear aircraft, door. This allows simultaneous boarding and deplaning of the aircraft from both doors. This type of bridge has been in use for several years in Europe and is starting to make an appearance in North America. Its limiting factor is expense, and the variety of aircraft serviceable with the rear bridge is limited and best suited to airlines operating only one or two types of aircraft.
The type of bridge has been picked, and now the options have to be faced. Glass bridges are becoming very popular in Europe, but they face fire regulation problems in North America, where the rules state that glass windows are prohibited. But these bridges are really glass-walled, not glass-windowed, and there is also the question of cost and cleaning. `Intelligent' bridges that can dock with the aircraft on their own have an obvious advantage, but many are reluctant to hand over control to a machine when expensive aircraft are involved. With heating, air-conditioning and ground power access, the options are endless.
Passenger Boarding Bridges provide a complete and seamless solution for the airport. In the end, the right bridge truly depends on the application and the ability of the person specifying that bridge to understand its application and all the constraints and limitations involved.