A PROJECT ABOUT AEROBRIDGES

HISTORY OF THE AEROBRIDGE

Boarding aircraft dated back to 1900 when Wilbur Wright built his first glider where he climbed into his seat in the glider. As technology advanced allowing aircraft to carry small number of passengers due to its size, boarding was done via stairs which were part of the aircraft door. This was possible as aircraft were generally lower in height, thus allowing the stairs to be fitted on the door. This method of boarding is still used today on small regional aircraft such as the Canadair CL-600-2C10 Regional Jet CRJ-700. As seen on the photo to the right, this aircraft uses stairs on the front left door to embark and disembark passengers and crews. As this method is very much restricted to being used on small aircraft with a low height, larger aircraft required a different method of loading.

This was overcome by using external stairs to connect from the aircraft door to the ground. This method can be used on virtually all commercial passenger/ cargo aircraft.

Originally, these stairs were made of mild construction steel or aluminum and are manually moved by ground staff. These fixed units maybe easily moved by ground staff when serving small aircraft such as the Boeing 737s as shown above on the left and centre photos. However, problems arise when serving larger aircraft and at larger airports. For serving larger aircraft, the stair unit would be larger thus creating problems for ground staff to move the unit as they could reach over 5 meters in height. Also, at large busy airports, it would be virtually impossible to move these stair units around the airport manually. This problem was solved by simply building the stairs above a truck which would simply ‘drive’ the stairs to the aircraft. This allowed transportation of large stairs and also moving it at a quicker speed.

REASON FOR INTRODUCING THE AEROBRIDGE

The main reason for introducing the aerobridge is mainly for passenger comfort. However, it was only possible with the advancement in technology in the 1970s where manufacturers were able meet the mechanical requirements for the operation of the aerobridge. Also, the box girder bridge construction contributed to the development of the aerobridge as the aerobridge is of a box girder construction. There was not much influence on the material side as aluminum and mild construction steel were available before the time aerobridge was introduced.

Considering the social side for introducing the aerobridge, one of the main reasons was to serve disabled passengers without great difficulties. Their immobility may prevent them from using stairs, thus creating a problem as they may need crews to carry them onto the aircraft and will also likely to slow the boarding process. If the boarding process took longer than expected, the flight may miss their time slot for take-off and clearance thus causing delays. Another problem the aerobridge solved was sheltering passenger from the weather. At stormy, rainy weathers, passengers are likely to get wet while walking to the stairs. Even once on the stairs which provides an overhead covering, they may get wet due to the uncovered sides. The aerobridge provided a ‘shelter’ for passengers as the aerobridge is in the form of a ‘tunnel’ where it shields the weather from the passengers inside. Also the aerobridge is connected to the terminal building which means that passengers need not to walk outdoor to board the aircraft, as the aerobridge is of a box girder construction, passengers walk inside the ‘tunnel’ of the aerobridge. This method of boarding and disembarking will save a considerable amount of time which is to the advantage of the airline as the turnaround time for the aircraft is shorter thus allowing the airline to maximize the usage of each aircraft.

Since the introduction of the first aerobridge, there were several improvements made to aerobridges. As mentioned in the previous section, one of the earliest types is made of aluminum which is not corrugated (Pedestal Bridge). Although it is light in weight but aluminum would limit its strength considerably. Problem arises when using aluminum since it burns easily and quickly thus may not be manufactured nowadays as it would not meet the safety requirements.

The improved type of aerobridge manufactured and used nowadays is made out of mild construction steel which is corrugated (Apron Dive Bridge). This provides extra strength and with its coating of fire resistant paint, it can withstand fire for up to 45 minutes which meets the fire safety standard (NFPA-417). The newest type of material used on aerobridge is glass as its side panels. This uses the construction of trusses to support the bridge and is also preferred as glass will not corrode.

The earlier types of aerobridges have fixed supports at both ends which limited its movements thus restricting the number of different types of aircraft the bridge may serve. As mechanics improved, aerobridges were constructed to having a pivot support at the end closest to the terminal and a roller support at the end closest to the aircraft which allowed the aerobridge to serve a wider range of aircraft. The roller support is created by installing wheels on the end closest to the aircraft which maybe driven changing the position of the aerobridge.

COMPOSITION OF THE APRON DRIVE PASSENGER BOARDING BRIDGE

SUPPORTS USED ON THE AEROBRIDGES

There are two major types of aerobridges. One uses fixed supports* at both end of the bridge (Pedestal Bridge) while the other type have a pivot support* at the end closest to the terminal and a roller support* at the end closest to the aircraft. (Apron Drive Bridge)

The Pedestal bridge have fixed supports at both the terminal end and at the aircraft end and may only serve a limited range of aircraft as different types of aircraft have different door height in relations to the ground and any aerobridges may not create a slope greater than 8.33% for passenger comfort. The fixed support also requires the aircraft to be stopped at a near exact position to the cab. The Pedestal Bridge is suitable and useful at terminals which serve a large number of same types of aircraft such as T2 and T3 of the Sydney Airport as these domestic terminals handle a large number of Boeing 737s, therefore several gates maybe designated to serve the particular type of aircraft. Using the pedestal bridges are also advantageous when only a limited types of aircraft use the gate as there are less number of serviceable parts in the pedestal bridge comparing to the apron drive bridge. This would minimize the chance of failure. This is attractive to airport operators as reliability is very important because failures causing the gate to be out of use will lead to delays and inconvenience of passengers.

However, when a range of aircraft are to use the same gate, the Apron Drive Passenger Boarding Bridge (PBB) is more suitable as it may serve a large variety of aircraft since it is capable to move to a range of position. The PBB has a pivot support at the terminal end and a roller support at the aircraft end. This allows the PBB to swing a total of 175 degrees (87½ degrees both clockwise and counterclockwise) and also have the ability to extend out a greater length allowing serving a wide range of aircraft. As noted above, any aerobridge may not generate a slope greater than 8.33% as it may create problems for passengers boarding the aircraft Therefore, for the PBB to serve in the same gate both large aircraft such as the Boeing 747-400 and small aircraft such as the Boeing 737s, which has a door height difference of over 2 meters, the rotunda at the terminal end is positioned at the average height of the minimum and maximum door height of the aircraft which it’s designated to handle. Then since the tunnels maybe extended or contracted as the tunnel section comprises of two or three different size tunnels which is fitted inside each other, this may compensate for the slope the PBB will create to meet the height requirement. i.e. as the slope is the gradient of the PBB and has the formula of rise over run, therefore for the same value of rise, increasing the value of run will make the slope gentler while with the same value of rise in a short run distance, the slope will be a lot more sharp thus causing passenger discomfort. Thus the PBB can serve a wider variety of aircraft as the roller support allows the PBB to be extended and contracted. In practice, using the PBB for a larger aircraft will result in less of the tunnel being extended out as larger aircraft have a taller door height while smaller aircraft uses a greater length of the tunnel as they have a lower door height and the extended tunnel compensate the change in height.

The pivot support is suitable in the PBB as it allows the PBB to swing to its desired position to meet the door position of the aircraft since the aircraft may not stop at exactly where the tunnel of the PBB has been pre-positioned. In fact, the rotunda at the aircraft end provides another pivot support for the cab which rotates about the rotunda. This pivot point will allow further adjustments to position the cab to meet the aircraft door.

METHOD OF CONSTRUCTION OF THE AEROBRIDGE (BOX GIRDER)

The method of construction of the aerobridge is the box girder construction as the aerobridge is essentially a tunnel in the shape of a rectangle prism. The aerobridge uses the box girder construction as this construction provides a rigid structure which is strong in strength including torsional strength as the box type construction can withstand twisting force (torque) to a large extent. Ability to withstand torque is imperative as airports are often located in open areas or adjacent to waterfronts which are susceptible to strong wind, thus the bridge need to withstand such twisting force. Another reason for using the box girder construction is that passengers can walk through the ‘box’ which shields the weather from them.

The aerobridge ‘sits’ on two supports which are the footing of the bridge. These footings can either be both fixed supports or pivot support along with a roller support. Fixed supports are bolted into the high strength concrete ground of the airport apron. This is done by using large size nuts and bolts to fix the position of the metal support (footing) to the ground. Another method for settling the supports into the concrete ground is to embed the support into the ground by pouring concrete around the support.

Pivot supports are joined to the ground by using nuts and bolts identical to the fix supports. This is possible as the pivot point is well above the ground up at where the rotunda is.

The roller support is not fixed to the ground but the wheels of the support are in contact, thus the aerobridge maybe moved.

The construction method to make the aerobridge is by joining the corrugated mild construction steel sheets together to provide the box type tunnel. This joining is done by the method of welding. The welding must comply with the American Welding Society (AWS) standard. The type of welding is fusion welding which provides great strength. This allows the metal sheets to join together to create the tunnels of the bridge.

In the aerobridges with fix supports, the tunnel is fixed onto the supports by means of nuts and bolts to hold the two members together.

The rotunda is fixed on either the pivot support by using nuts and bolts to hold the two components together. It also uses ball bearings for the rotational function. The tunnel also uses ball bearings internally to connect to the rotundas on both ends for its rotational purpose.

The roller support is fixed to the tunnel by means of nuts and bolts. The vertical movements of the roller support are possible as the columns connected to the tunnel are joined into another column of support which is in contact to the wheels. The vertical movement uses a system of two re-circulating ball bearing screw assemblies moving the column up and down one part of the column system is screwed to the tunnel. The vertical movement speed can reach up to 1097mm per minute. The wheel unit of the roller support is also fixed to the other member by means of nuts and bolts. The horizontal movement uses an electro-mechanical drive system to move outwards with the aid of ball bearings inside the tunnels.

All the metal components of the aerobridge are Commercial Blast cleaned then painted with Sherwin Williams High Build Epoxy Primer paint as the base coat and the finishing coat is Sherwin Williams Polane Polyurethane topcoat. The blast cleaning will ensure excess material and intruding materials be cleaned away to minimize chance of corrosion and the painting will prevent corrosion by the weather. The painting also will make the metal fire resistance for 45 minutes to meet the fire safety standards.

MATERIALS USED IN THE AEROBRIDGE AND ROLES OF MATERIALS

LOADING OF THE AEROBRIDGE

Since the main purpose of the aerobridge is to provide a passage way for passengers to board and disembark from the aircraft with their hand carry baggage, the maximum loading will not be too great. The maximum loading is very much depended on the length of the aerobridge as the cross sectional length is all standard. Maximum loading shall only be estimated for the Apron Drive Passenger Boarding Bridge as this is the main type of aerobridge used nowadays. There are two types of Apron Drive PBB used in Sydney Airport at the moment, the two tunnel model and the three tunnel model. The difference between the two types is the number of tunnels which the tunnel section is comprised of. Three tunnels will result in conserving space when the PBB is fully retracted but fully extended length are not depending on the number of tunnels.

According to the “Airport Equipment Ltd/ Jetway Systems” General Specification, the maximum live load for the PBB is 195kg/m². Calculating this figure with the different models of PBB available, the shortest PBB (Max. operating length of 12.497m) can withstand a load of 3460.4193kg equivalent to 46 average adults of 75kg each or 42 average adults with carry on baggage of 7kg each. The longest PBB (Max. operating length of 42.673m) can carry a maximum load of 11816.1537kg equivalent to 157 average adults or 144 average adults with carry on baggage of 7kg each.

The PPB need to also withstand a wind load of 122kg/m² (145hm/hr) when unused and an operational wind load of 61kg/m² (97hm/hr).

A roof load of 122kg/m² is also required when technicians and engineers are required to work on the roof.

The base of the tunnels comprise of corrugated ASTM-A36 medium carbon construction steel to withstand this load along with a centre beam running perpendicular to the corrugated patterns.*

ENGINEER’S ROLES

To design and manufacture an aerobridge, several types of engineers need to cooperate together so that the final product maybe manufactured. Different types of engineers include Electrical Engineers, Material Engineers and Mechanical Engineers.

Electrical engineers have the role to connect electrical power from the ground source to the aerobridge so that electrical power can provide lighting inside the aerobridge through fluorescent light tubes and also controlling the aerobridge maybe possible as the aerobridge is driven by a joystick which connects to the computer that requires electricity to run on. Electrical power is also required for outside flood lights on the aerobridge while operating at night or at adverse weather so that the aerobridge maybe seen at a distance. The electrical engineer also needed to design an electrical system which is well protected from the weather and from people passing through the aerobridge for safety requirements. To solve this problem, all the electrical cables and other operation related cables are located underneath the tunnel which has limited shelter from the weather and cannot be reached by passengers. Since the horizontal drive of the aerobridge uses an electro-mechanical drive system, electrical power is also required for this purpose.

Material engineers have the role to choose the correct materials to be used in the construction of the aerobridge. Choosing the correct material is imperative as the material is needed to withstand the expect load and work under a range of different weather conditions. The material engineer also needs to select materials that will be reliable and be used for a long period of time without the need of constant maintenance and repairs.

Mechanical engineers are required to design an efficient way to operate (move) the aerobridge for its usage. This includes making the aerobridge move outwards/inwards, upwards/downwards and also swing to meet the aircraft door. The mechanical engineers need to find the way to operate without the excessive use of power and resources.

Thus designing and manufacturing an aerobridge is a big project requiring various types of engineers from different fields to work as a team to design and manufacture an aerobridge that is widely used nowadays.

FUTURE DESIGNS

Although the Apron Drive PBB is sufficient for today’s aviation industry, improvements are being continuously thought of to minimize aircraft turn around time thus maximizing the usage of each single aircraft. This resulted in busy airports having 2 separate apron drive PBBs at each gate so that passengers may board and deplane the aircraft at a much quicker rate. The best example is at Hong Kong Chek Lap Kok International airport where there are 2 independent apron drive PBBs serving each gate so that First and Business class passengers may board the aircraft using one PBB while Economy class passengers board via the other PBB. Although this will not save too much time during the boarding process as passengers are restricted to which PBB they may used, but having 2 PBBs can save a considerable amount of time for when passengers deplane on arrival. Once the First and Business class passengers have deplaned via their designated PBB, the remaining Economy class passengers may also use the First and Business class passenger’s PBB to deplane thus saving time. This concept is imperative for larger planes as there could well be over 350 passengers on the plane at one time thus will take some time to board and deplane all passengers. Especially when the Airbus A380-800 comes into service in 2006, dual PBB must be used as this aircraft is capable of carrying 550 passengers.

Another improvement on existing apron drive PBB is the Glass Boarding Bridge where the side panels of the tunnels are made of glass. The main reason for this improvement is for consumer’s requirement as it provides passenger with a clear view of the apron prior boarding their aircraft.

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