A ULD (Unit Load Device) is a certified air cargo container, or an air cargo pallet secured with a net, that allows air cargo to be loaded onto the aircraft as a unit. Containers such as the AKE (LD3) fit the lower deck of wide-body aircraft, while pallets such as the PMC fit both the lower deck and the main deck. The chosen ULD determines the size, height and weight limits of the cargo.
Why are ULDs used?
On wide-body aircraft, cargo is not loaded as individual cartons but in pre-built units. These units slide on the roller system in the aircraft floor and are secured with locks. This shortens loading time, allows the weight balance to be planned and keeps the cargo in place during the flight. IATA defines ULDs as removable aircraft parts subject to the design, manufacturing, maintenance and repair rules of civil aviation authorities. Around one million ULDs are in use worldwide, and the technical rules are compiled in the IATA ULD Regulations (ULDR) manual.
How do you read a ULD code?
Every ULD carries a three-letter type code, a serial number and the code of the owning airline; for example AKE 12345 TK. The letters of the type code mean the following:
- First letter, ULD category: A certified container, P certified pallet, R temperature-controlled (thermal) container.
- Second letter, base size: For example K indicates a base of approximately 156×153 cm, M approximately 318×244 cm.
- Third letter, contour and compatibility: Indicates which hold profile and locking system the unit fits.
Common types
| Code | Type | Base (approx.) | Use |
|---|---|---|---|
| AKE (LD3) | Container | 156×153 cm, height approx. 163 cm | Lower deck of wide-body aircraft; maximum gross weight approx. 1,588 kg |
| PMC | Pallet + net | 318×244 cm | Lower deck and main deck; height and weight limits vary by position |
| PAG | Pallet + net | 318×224 cm | Lower deck and main deck |
| RKN / RAP | Thermal container | Depending on type | Pharmaceuticals and temperature-sensitive cargo |
Dimensions and maximum weights vary by airline, aircraft type and hold position; exact values should be confirmed with the airline at booking.
Height and contour restrictions
On passenger aircraft, cargo is carried only in the lower deck and height is limited to about 160 cm. On the main deck of freighters, heights of up to about 300 cm are possible, but this too depends on the aircraft type and position. The edges of cargo built up on a pallet are shaped according to a contour profile that follows the curve of the fuselage. Cargo protruding beyond the profile prevents the pallet from being loaded onto that aircraft. This is why air cargo bookings ask for the dimensions of each piece separately; the dimensions also determine the chargeable weight.
Limits for heavy and oversized cargo
- Floor loading: The aircraft floor has a load limit per square metre; load-spreading planks are used for heavy pieces with a small footprint.
- Door size: The main deck door determines the largest cross-section that can be loaded.
- Long pieces: Cargo longer than a single pallet can be spread over several pallets; this requires airline approval.
- Charter: For pieces exceeding these limits, a chartered freighter is considered; see heavy cargo by air.
Who builds the ULD?
ULDs are usually built up in the warehouse of the airline or the ground handling company. Some airlines also accept pallets built by consolidating agents in their own warehouses; in this case loading, netting and contour checks are the agent's responsibility. The document structure for consolidated cargo is explained in the entry MAWB and HAWB. For temperature-controlled cargo, the choice of thermal ULD is planned together with the GDP rules for the warehouse and road legs.
Common mistakes
- Planning the height of palletised cargo without considering the lower deck limit
- Letting cargo overhang the pallet edge
- Skipping the floor loading calculation for heavy machine parts
- Confusing ULDs with ocean containers; air ULDs do not have the same dimensions and strength as ocean containers
How does Voltim Global support you?
For oversized or heavy pieces, Voltim Global starts air freight planning with a piece-by-piece list of dimensions and weights. Based on this list, the suitable aircraft type and ULD are determined together with partner airlines and air cargo agents.