Disposiciones Comunes

In the majority of commercial aircraft, cargo is carried below the cabin floor, in dedicated fire resistant compartments that can be air conditioned if animals are being carried. There are a number of different variations to the above, dependent on the size of the aircraft, the type of passenger, the routes flown, etc. In the Fokker 100, for example, most of the underfloor space is for baggage, excluding the extreme front, which is for avionic equipment.

Under Floor Baggage Holds Figure 7

Smaller aircraft such as the Dornier 227 and the Fokker 50 have their cargo carried within the cabin space, the underfloor space being limited. Aircraft at the other end of the size spectrum, known as 'wide body' aircraft, can be produced as dedicated freighters such as certain Boeing 747 models.

A more popular layout these days is the 'Combi freighter' which can carry both extra freight and passengers in the cabin, whilst still carrying cargo in the underfloor space. This type of aircraft is much more flexible on routes where the cargo/passenger ratios can vary through the week, the month or year. At times, there might be only 50 - 100 passengers on board whilst the remainder of the aircraft is carrying cargo.

Containers are typically boxes shaped to the contour of the aircraft fuselage to maximise the capacity of the freight bay. They can be made from, alloy honeycomb of fibreglass.

LD2

LD8

LD3

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Most containers are sized by a code established by an international agreement enabling aircraft manufacturers to build the freight bays to a common size. The width of the cargo bay determines the size of the containers that can be loaded, but by setting the position of the various guides on the cargo bay floor, more than one size of container can be carried.

Typical container sizes commonly used are shown above in various configurations. The identifying code letters indicate where the container has been designed to be loaded. Thus LD2 is a container of a standard size, designed for the lower deck (LD). Other sizes range from LD3 to LD8.

Automatic Cargo Loading Systems

Automatic cargo loading systems represent a major advance in the speed and efficiency that airfreight can turned round. Aircraft are designed to carry fare- paying passengers above the cabin floor and a vast amount of cargo underneath. With the use of an automatic loading system, one man can load many tons of equipment, usually stored in purpose built containers, in the time it takes to refuel the aircraft and board the passengers.

The Electro-mechanical loading system mechanism is normally built into the aircraft during manufacture. It consists of driver and sorter devices to load, store and manoeuvre the containers into the freight bay. The method of moving the containers is with the use of rubber-tyred rollers. These are in contact with the base of the containers and are motor-powered from the aircraft electrical system. Various guide rollers are used to steer the containers to the required location in the bay.

Loading and unloading

The containers are normally raised to the cargo bay floor level by a hydraulically operated deck, whose load area is covered with free running rollers or balls. The containers are then manually pushed into the door area, where they enter the freight bay of the aircraft and are supported by a ball mat or ball transfer panel. The ball mats/panels are low friction devices, which permit easy container movement. Each individual ball unit consists of a self-lubricated spring-loaded steel ball which itself rides on a series of smaller ball bearings in a cup-shaped housing. A wiper ring surrounding the ball prevents the ingress of dirt into the mechanism.

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Roller Ball Guide Figure 9

Once the load begins to enter the bay, the lateral rubber-covered drive rollers can be rotated to drive the containers fully into the bay. Lateral guides keep the container square and prevent the container from running off the edge of the transfer panel, as it is driven into the bay. Guide rollers around the doorframe ensure centralisation of the container and prevent doorframe damage.

Sill rollers are mounted to the lower doorframe (sill) to provide a rolling surface into and out of the door area. With the container fully into the bay, longitudinal rollers can be rotated to propel the container down the length of the bay, once the relevant lateral retaining guides have been lowered. Roller trays are mounted down the entire length of the cargo bay, to continue on the similar low friction surface as the ball mats, for moving the containers. Centre or auxiliary guides ensure the container travels longitudinally and squarely, down to the extremities of the bay.

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During unloading, the roll-out-stops are locked down to permit free passage of the container out of the bay. This is done electrically or by pressing a foot pedal on each roll out stop if electrical power is not available. The Power Drive Units (PDU) consist of an electric motor driving a rubber-tyred roller. When commanded to rotate from the control panel, the roller is raised approximately 12mm from the floor level by a cam. Only when the roller is raised, will it begin to rotate and apply a moving friction force to the base of the container to propel it over the balls and rollers.

Control Panel

Each cargo bay will have a control panel with switches for; system power on/off, cargo bay lights, raising and lowering of the various lateral and longitudinal guides. A joystick control with eight positions and centre-off is provided for power drive unit operation.

A Typical Control Panel Figure 11

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The sequence for loading LD2 containers into the cargo compartment is as follows:

1. Door fully open. 2. Power switch ON. 3. Select LD2 on panel.

4. Set roll out stops to load position. 5. Set lateral guides to NORMAL. 6. PDU switch to A-B ON.

7. PDU switch on the on the other panel to FWD ON. 8. Switch the lights on if required.

9. Place the container level with the doorframe of the compartment.

The joystick is then used to control the PDU’s and move the container into the desired bay. As the container clears each roller they spring up to prevent it rolling back out of the bay. At the end of the containers’ travel it contacts the fixed loading stops and with all the containers loaded the roll out stops are positioned into the locked up position, holding the load firmly.

Unloading.

Essentially unloading is the reverse of the loading procedure, with the exception of locking the roll out stops to their retracted position and positioning all of the centre/auxiliary guides to the down position.

If any guide has been manually locked down, ensure they are unlocked before electric power is applied to prevent damage to the motors. At the first sign of any container stopping or failing to move release the joy stick to the centre/off position and investigate the cause of the jam.

Only approved personnel, who have received proper training in the particular installation or layout, should carry out the operation of automatic loading systems.

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Dangerous goods are those which possess potentially hazardous characteristics. However, as long as suitable precautions are taken these goods are not necessarily prohibited from air travel. They include obvious items such as; acids, explosives and radio-active materials and also some unlikely items such as magnets, breathing apparatus and other gas cylinders and instruments that contain mercury.