Unit Load Device (ULD)

A unit load device (ULD) is a pallet or container used to load air cargo, baggage and mail onto an aircraft. Instead of loading thousands of loose cartons, the airline or its ground handler assembles the cargo into a few large units that roll across the cargo floor and lock into the aircraft's restraint system. IATA's ULD Regulations set the standards, and each ULD carries an identification code such as AKE 12345 DL: a three-letter type code, a serial number and the two-character code of its owner, usually the operating airline.

Pallets and containers

• Pallets: a flat aluminum base onto which cargo is stacked and held down with a net and straps. Pallets take irregular and oversized pieces and are the usual ULD on a freighter's main deck
• Containers: enclosed units with a base, walls and a roof, often with a sloped side that follows the curve of the lower hold. They protect the contents, load quickly, and are how baggage travels on most wide-body aircraft

Common types and published dimensions

Airlines publish figures for their own ULDs, which differ slightly; these are the commonly published values.

• LD3 (IATA type code AKE): the most common lower-deck container on wide-body aircraft. Base 156 × 153 cm (61.5 × 60.4 in), height 163 cm (64 in) and width 201 cm (79 in) across the sloped overhang, with about 4.3 m³ of internal volume and a maximum gross weight of 1,588 kg (3,500 lb)
• PMC: a 318 × 244 cm (125 × 96 in) pallet with a net, used on the lower deck of wide-body aircraft and on freighter main decks. Its maximum gross weight is commonly published as up to about 5,100 kg (11,250 lb) in the lower deck, depending on the aircraft, and 6,804 kg (15,000 lb) on the main deck
• PAG: a 318 × 224 cm (125 × 88 in) pallet, a little narrower than the PMC, used on both decks

Belly vs main deck

Passenger aircraft carry cargo in the lower deck, or belly, below the cabin. The hold height there limits a ULD to about 163 cm (64 in), so tall pieces do not fit. Freighters also load the main deck, where pallets can be built much higher: commonly to about 244 cm (96 in), and to about 300 cm (118 in) on large freighters. Narrow-body aircraft carry smaller containers or loose, bulk-loaded pieces, which limits the size of what they take.

Why it matters to a shipper

• Build-up and breakdown: at origin, cargo is built up onto ULDs in the airline's or handler's warehouse; at destination it is broken down again before release. Both steps take time, which is why airlines set acceptance cut-offs hours before departure and why cargo is not available the moment the aircraft lands
• Contour limits: a ULD is built to a contour, the profile that fits the aircraft's fuselage and doors. A piece too tall or too wide for the contour on the flight booked may have to wait for a freighter or take a different routing, so give exact dimensions at booking
• Weight limits: each ULD has a maximum gross weight, and very heavy, compact pieces can need boards underneath to spread the load across the pallet
• Billing: general cargo is billed on chargeable weight, the greater of the actual weight and the volumetric weight, so shapes that leave dead space on a pallet cost more to fly

On air freight booked through Airlift, the airline or its ground handler builds the ULDs. Accurate piece dimensions and weights at booking are what make sure the cargo fits the aircraft it is booked on; the chargeable weight calculator accepts dimensions in inches or centimeters.