Overview
Air freight unit load device (ULD) contouring is the planning and building of cargo on an aircraft pallet, or the selection and loading of an aircraft container, so that the completed unit fits the permitted aircraft loading envelope. The contour reflects constraints such as the cargo door, compartment shape, loading position, and clearance around the aircraft structure.
A ULD groups cargo into a unit that can be handled and loaded as part of an aircraft cargo system. Contouring aims to use available space efficiently without exceeding dimensional, weight, restraint, or handling limits. It is related to general palletization, but aircraft ULDs require aircraft-specific checks that a conventional warehouse pallet build does not establish. Facilities may coordinate cargo staging and piece dimensions with specialized palletization software before transferring freight into aviation-specific ULD build areas; that software does not itself establish an aircraft contour or flight acceptance.
Etymology and Origins
Contour refers to an outline or shape; in this context, it describes the permitted outer profile of a loaded unit. Derived from the Italian contornare ("to draw an outline") and the French contour, the ordinary meaning of contour helps distinguish the aircraft loading envelope from the rectangular footprint of a pallet base.
Unit load device is the aviation term for a cargo-handling unit such as an aircraft pallet or container. The terminology developed around the need to identify and handle standardized units within aircraft cargo systems; IATA’s ULD guidance describes their role in air transport. Identification and technical requirements are set out in the IATA ULD Regulations, which classify containers and pallets by type, base dimensions, and contour or compatibility codes. Those regulations should not be confused with the IATA Standard Schedules Information Manual, which concerns airline schedules rather than ULD build profiles.
Historical Development
Cargo was initially loaded and restrained as individual pieces ("breakbulk"). The growth of larger aircraft and mechanized ground handling made preassembled cargo units increasingly useful, shifting some work from the aircraft hold to the cargo terminal. The Boeing 747 entered commercial service in 1970, a prominent milestone in wide-body aviation. Its large lower-deck and main-deck cargo spaces made aircraft-specific loading profiles, including contoured lower-deck units such as the LD-3 (commonly coded AKE) and curved main-deck builds, operationally important. The 747 did not create every later ULD type, but it is a well-documented point at which standardized wide-body containerization became central to scheduled cargo handling.
Over subsequent decades, airline and industry procedures increasingly formalized ULD identification, serviceability, build-up, and handling. FAA Advisory Circular AC 120-85A, Air Cargo Operations, provides guidance on air-carrier cargo operations, including weight-and-balance and restraint considerations; it is guidance, not itself an operating specification. The IATA ULD Regulations consolidate industry technical and handling requirements, including widely used base sizes such as 88-by-125-inch and 96-by-125-inch pallets and associated contour codes. Planning has also evolved from manual measurements and physical contour gauges toward computerized load planning and volumetric modeling. A digital plan does not replace physical verification or the carrier’s acceptance process.
Core Concepts
The loading envelope
A contour is a three-dimensional limit, not just a maximum height. A pallet may have a rectangular base but require a sloping or stepped upper profile to clear the curved fuselage. Permitted dimensions can differ by aircraft type, deck, position, ULD type, and carrier procedure. A load that fits one position is not automatically acceptable in another.
The planner should obtain the current carrier-approved contour and account for cargo, packaging, nets, straps, and any projections. The IATA ULD Regulations are a starting point for ULD handling requirements; the operating carrier’s loading instructions determine the actual acceptance criteria for a flight.
Geometry, mass, and restraint
A compliant build must satisfy several independent checks:
- Fit: The completed unit stays within the applicable profile and required clearances.
- Gross mass: Cargo, packaging, dunnage, restraint equipment, and the ULD itself remain within all applicable limits.
- Weight distribution: Concentrated loads and the unit’s center of gravity comply with the carrier’s and aircraft limits, including any published area-load restrictions.
- Restraint: Cargo is secured against movement using the approved system and methods.
- Serviceability: The ULD and its restraint components are acceptable for use and compatible with the intended aircraft system.
Aircraft design rules address restraint of cargo and baggage in stowage compartments. Related certification standards for emergency landing conditions specify load factors that restraint systems must be shown to meet. Industry specifications such as SAE AS18286 cover design criteria for aircraft cargo restraint straps; they do not, by themselves, approve a particular net, corner fitting, or completed build. A load can be dimensionally correct yet unacceptable if its weight distribution or restraint is inadequate.
Illustrative build
A forwarder building mixed cartons on an aircraft pallet may place dense, adequately supported freight low in the build and use smaller cartons to step the upper layers back beneath a sloping side profile. After applying the approved net and other required restraints, staff check the finished unit against the carrier’s template or measuring method and weigh it. This is an illustration, not a substitute for the applicable contour chart or restraint instructions.
Types and Classifications
Palletized ULDs consist of an aircraft pallet with cargo built up and restrained on it. Their flexible load shape can accommodate mixed freight, but staff must construct and verify the outer profile, often with contour frames, gauges, or measurement systems. Aircraft containers have defined structural shells, often shaped for a particular aircraft compartment; their exterior shape does not remove the need to respect internal loading, door, restraint, and weight limits. Both are covered by IATA’s ULD framework.
Operationally, handlers distinguish lower-deck units (such as the half-width AKE/LD-3 and the AKH/LD-1 family used on some wide-body aircraft) from main-deck builds on pallets such as the PAG (88 by 125 inches), PMC (96 by 125 inches), and longer 16-foot and 20-foot pallets. Exact codes, contours, and aircraft compatibility are carrier- and position-specific. Conventional palletization practices can help organize cartons, but aviation rules require alignment with the carrier’s published weight, balance, and contour limits.
Operational Workflow and Best Practices
- Confirm the booking and equipment. Obtain the aircraft, deck, intended ULD, destination, and applicable carrier contour and build instructions. Reconfirm if the flight or aircraft changes.
- Inspect and prepare. Check ULD serviceability, including the base, edge rails, and restraint attachment points, together with restraint equipment and cargo packaging. Identify handling restrictions, incompatible goods, and any special approvals before build-up.
- Plan the load. Measure pieces and establish gross weights, stacking limits, and orientation. Place heavy or concentrated pieces in accordance with the carrier’s distribution and floor- or area-load limits. Upstream teams may group orders with shipping and fulfillment software before pallet assembly; that grouping is not an aircraft load plan.
- Build and secure. Keep the planned profile within limits while protecting cargo from crushing or shifting. Use only the approved nets, straps, and tie-down arrangements, with protective materials where the carrier’s instructions allow them.
- Verify and document. Check the physical build against the required contour method, confirm gross mass on a suitable scale, verify ULD identification, and complete the carrier’s build or control documentation. Resolve discrepancies before presenting the unit for acceptance.
The IATA ULD Regulations provide a reference for ULD handling and operational controls. Warehouse systems can support upstream packing and fulfillment workflows, but general warehouse software should not be assumed to validate a carrier’s aircraft contour or approve a ULD for flight.
Safety, Special Cargo, and Limitations
The usable space inside a contour is not necessarily fully available for cargo. Restraint geometry, package strength, ventilation, access, segregation, and handling clearances can leave unavoidable voids. Overbuilding to reduce empty space can cause a unit to fail acceptance or require a costly rebuild.
Dangerous goods require checks beyond physical fit, including classification, packaging, documentation, handling, and any applicable segregation or loading restrictions. Consult the current IATA Dangerous Goods Regulations and the operator’s requirements. For all cargo, applicable aircraft cargo-restraint requirements, the relevant emergency-landing load criteria, and the carrier’s approved procedures take precedence over a generic optimization plan.
Changes in aircraft assignment, inaccurate dimensions, damaged ULDs, and undocumented weight estimates are common sources of rework. A practical control is to record the reason for each rejected or rebuilt unit and use those records to improve measurement, packaging, and build planning.