Loading of Aircraft with Cargo
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Safe operation of aircraft requires all hold cargo and baggage to be weighed (or an accurate estimate of weight provided by using “standard” values), it must be loaded correctly and secured to prevent movement in flight.
Loading should be in full accordance with the generally applicable regulations and limitations, the operators loading procedures and in accordance with the instructions given by the person with overall responsibility for the loading process for a particular flight. These loading instructions must match the requirements for baggage/cargo distribution stated within the aircraft load and trim sheet.
The Operational Safety Issues
In recent years security considerations have led to rigorous procedures to ensure ‘baggage reconciliation’, which ensures only accompanied baggage is loaded, unless a special additional validation process for each unaccompanied bag has been followed.
Weight distribution between holds has a considerable effect upon the C of G of the aircraft; load distribution will be specified on the Loading Instruction Form (LIF) by hold, or by hold compartment in the case of larger under floor hold areas..
Many narrow body short haul aircraft are bulk loaded with loose individual items of baggage and cargo. In this case, baggage loading will be by item count, with prescribed assumptions about the average weight per bag used to complete the load and trim sheet; precise figures will often vary according to National Aviation Authority (NAA) regulations or be more restrictive to meet the aircraft operator’s own checked baggage rules. Average checked baggage standard weight assumptions usually vary depending on whether the flight is domestic, international, charter (holiday flight) or scheduled. Standard baggage weights must be applied with care. Incidents have occurred where standard weights have seriously under-stated the actual mass of the loaded baggage causing both an error in the total mass of the aircraft and a centre of gravity outside the approved safe envelope.
Netting is used to restrain bulk loaded loose baggage items within holds so that they do not move in flight. Any load that shifts in flight will move the aircraft’s centre of gravity and can cause control difficulties (in extreme cases causing loss of control) and prevent baggage door opening post flight. Cargo netting may also be used to divide larger holds into sections.
Bulk Loading is usually accomplished by delivery of items to the aircraft in a baggage train of towed trailers. To help ensure each hold compartment is loaded correctly, a particular trailer may only contain the baggage destined for only one designated compartment. The trailer is unloaded into the aircraft hold via conveyor belts and finally positioned in the hold by loaders working within it. Usually, bulk loading of baggage items uses a system whereby loading crews are informed that the last bag for loading on a particular flight has arrived by use of an ‘End Bag’ identification tag - the tag is applied to the last checked bag sent to the aircraft. A system of stickers and a reconciliation sheet may also be used, where each printed baggage tag has a bar-coded sticker, which is removed and stuck onto the re-conciliation sheet as the bag is loaded. This helps ensure that all checked baggage for that flight has been loaded and accounted for.
Unit Load Devices
Most wide bodied aircraft, and increasingly some narrow bodies, are able to use the much simpler system of aluminium containers called Unit Load Devices (ULD) (ULDs). These can be used to consolidate baggage or cargo items before being loaded into the aircraft hold by specialised hydraulic lift equipment. The ULDs are then manoeuvred manually to a final position on board by use of a roller floor, before being finally secured in position.
ULDs must either be weighed, or the number of baggage items per container must be within a specified range and standard baggage unit weights applied.
Under either system, special procedures may be prescribed for abnormal loads such as:
- those covered by Dangerous Goods Regulations
- heavy items
- oversize items
- items with have unusual dimensions/proportions.
Heavy objects which exceed the hold floor-loading limit published in the Aircraft Flight Manual (AFM) may be able to be carried if prescribed arrangements for load spreading are available and applied.
Mass and Balance Gross Error Checks
A load instruction/report form will be issued for every aircraft departure to instruct loading teams on the quantity of baggage/cargo to be loaded into each hold. Where a computerised or electronic load and trim sheet is prepared on behalf of the operating crew, usually the handling agent or airline will produce the Load Instruction/Report Form with reference to the load and trim sheet. The Load Instruction/Report form will then be given to the loading supervisor to instruct the load team how the aircraft needs to be loaded and to record formally the actual loading and any deviations.
When the operating crew produces a manual load and trim sheet, the crew, in consultation with the loading supervisor, may also complete the Load Instruction/Report Form.
Once the aircraft is loaded, the Load Instruction/Report Form is generally provided to the crew for cross-checking against the load and trim sheet, though sometimes the crew are provided with a certificate stating that the baggage/cargo has been loaded in accordance with the load and trim sheet instructions.
With numerous mass and balance documentation formats and different industry procedures, it is very difficult to provide definitive details of how to conduct gross error checks. In line with the best industry practices, UK CAA guidance material - CAP 1009: Gross Error Checks provides information on how any significant discrepancies in the loading process can be identified and corrected before departure.
As with the load and trim sheet, there are a number of key entries on the Load Instruction/Report Form that must be checked for accuracy:
- Flight details (Routing, Flight number and Date)
- Aircraft type, variant and registration
- Distribution of hold loads (including baggage, cargo, ballast, spares, COMAT, and mail etc.)
- Void/nil fit positions
- Bags per ULD/hold
- Weight allocation to each compartment does not exceed limits
- Document edition number (if applicable)
Principal Hold Loading Risks
The principal risks associated with loading of aircraft holds are as follows:
- Holds are not loaded by the loading crew in accordance with the Loading Instructions provided - and the Load Instruction/Report Form is not amended to reflect these changes.
- Where the loading has been different to the original Loading/Report Form and the Loading/Report form is updated, the last minute change (LMC) has not been correctly applied to the original loadsheet calculations and checked for mass and balance limits.
- The load is not secured or restrained appropriately
- Unauthorised items are loaded (e.g. dangerous goods).
- Aircraft structure (or propeller blades if applicable) is damaged by unintended impact from mechanised loading equipment. Such impacts may go unnoticed by the loading team or in some cases is noticed but not reported. This may happen when the load team can see no apparent damage so consider reporting the impact unnecessary. Where the aircraft structure is formed using composite materials, all impacts must be reported. While evidence of significant damage to a metal structure is usually clearly visible, this is not necessarily true for composite materials. Although the skin may appear to be undamaged, the core of a composite structure may have deformed or have been significantly weakened.
Consequences of Mis-loading
- Loss of Control in flight
- Runway Excursion during take off or landing
- Aircraft Hold Damage during flight
Accidents and Incidents
The following events listed on SKYbrary are related to Cargo Loading:
- UK CAA CAP 1008 Last minute changes (LMC) - Guidance document, February 2014
- UK CAP 1009 Gross error checks - Guidance document, February 2014
- UK CAA CAP 1010 Ramp/ Aircraft Loading Operations Checklist, February 2014
- FAA AC 120-85A 'Air Cargo Operations', June 2015
- ISAGO Standards Manual 5th Edition, March 2016
- FAA SAFO on 'Cargo Restraint Strap Assemblies', July 2016
- FAA SAFO 17004: Cargo Retention Methods Using Pallets Straps, March 2017