ULD Types

What Is a ULD?

A Unit Load Device (ULD) is a standardised container or pallet used to load cargo, baggage, and mail onto aircraft. ULDs are built to strict IATA and airline specifications so they lock securely into aircraft cargo holds. Each ULD type has a unique IATA code (such as AKE for the LD3 container) that identifies its dimensions, weight limits, and compatible aircraft.

Using ULDs dramatically speeds up aircraft loading and unloading. Instead of handling individual packages, ground crews move pre-built ULD units with dollies and loaders. A wide-body freighter like a Boeing 747F can carry over 30 ULD positions across its main and lower decks.

Lower Deck vs Main Deck

Aircraft cargo space is divided into two areas. The lower deck (also called the belly) sits beneath the passenger cabin on passenger aircraft or beneath the main deck on freighters. Lower deck ULDs like the LD3 (AKE) and LD9 (AAP) are contoured to fit the curved fuselage cross-section, which is why they have angled sides. The main deck is the primary cargo floor on freighter aircraft, accessed through a large side-loading door. Main deck pallets and containers (PMC, AMJ, PAG) are larger and rectangular because the full fuselage width is available.

Passenger airlines only use lower deck ULDs for cargo (the main deck carries passengers). Freighter aircraft use both decks, giving them significantly more cargo capacity. Some ULD types like the PLA (P1P) pallet are designed to work on both decks.

How ULDs Are Used in Air Cargo

The process of loading cargo into a ULD is called buildup, and unloading is called breakdown. During buildup, individual shipments are stacked inside the ULD, weighed, and secured with nets or straps. The completed ULD is then transported on dollies to the aircraft and loaded using high-loaders or roller systems built into the cargo hold floor.

Airlines own and manage most ULD fleets, tracking each unit with unique serial numbers. Freight forwarders and shippers typically do not own ULDs — they deliver loose cargo to the airline or ground handling agent, who performs the buildup. Some large freight forwarders have agreements to build up their own ULDs at warehouse facilities, returning the completed units to the airline for loading. Accurate ULD weight declarations are critical for aircraft weight and balance calculations.