Air cargo ULD types: containers, pallets and aircraft compatibility

A ULD (Unit Load Device) is the collective name for the standardised containers and pallets on which air cargo is built up before loading. Every ULD is shaped to the cross-section of the aircraft hold, locks into the aircraft's restraint system and is certified by aviation authorities; it is not an ordinary crate or pallet.

Shippers need ULD knowledge for two reasons: it determines which piece can fly on which aircraft and the weight on which freight is charged. The figures below reflect industry standards; manufacturers and airlines vary slightly, so all dimensions are approximate.

Containers or pallets?

ULDs fall into two groups. Containers are closed units with aluminium or composite walls and a door. Pallets are flat aluminium sheets with a locking rail around the edge; cargo is stacked on them and secured with a net. Pallets accept bulky pieces as long as they fit the aircraft contour; containers protect cargo from weather and handling damage.

Each ULD carries a three-letter type code. The first letter gives the category (A: certified container, D: non-certified container, P: certified pallet, F: non-certified pallet), the second the base size (K: 60.4 × 61.5 in; A: 88 × 125 in; M: 96 × 125 in; G: 96 × 238.5 in; Q: 60.4 × 96 in) and the third the contour and compatibility class. A serial number and the owner airline's code follow, for example AKE 12345 TK.

Main container types

Container volumes are usable volumes: the lower corner is chamfered to follow the fuselage contour and the door opening is smaller than the external footprint. The AKE door, for instance, is approx. 140 × 150 cm, and every single piece has to pass through it.

Pallet types

For pallets the decisive figures are the base size and the contour height of the deck they will occupy. The same PMC pallet takes roughly 160 cm of cargo height on a lower deck, 244 cm on a freighter main deck and up to 300 cm on the B747F and B777F.

Which aircraft takes which ULD?

Narrow-body aircraft: the lower deck of the A320 family (A319/A320/A321) takes between 4 and 10 AKH (LD3-45) containers depending on the variant; piece height is limited to approx. 110 cm. The passenger B737 family takes no ULDs at all: cargo is loaded loose (bulk) by hand and single pieces are limited by the cargo door, approx. 120 × 90 cm.

Wide-body passenger aircraft (A330, A350, B777, B787, B747): each lower-deck position takes two AKE side by side or one PMC/PAG pallet. Cargo height is limited by the lower-deck contour, approx. 160 cm. The belly capacity of these aircraft is a major source of cargo supply. The B767 is the exception: its narrower hold uses LD2 (APE/DPE) and LD8 (DQF) containers.

Freighters (B747F, B777F, A330F, B767F): the main deck allows cargo up to 244 cm high, and up to 300 cm on the B747F and B777F; PMC, PAG, AMA and the 20 ft PGA travel here. The nose door of the B747F adds flexibility for long project pieces. The lower deck takes the same ULDs as passenger aircraft.

The contour is the cross-sectional profile a loaded ULD may occupy without touching the fuselage. Lower-deck contours have a chamfered corner that follows the hull curve; main-deck contours are close to rectangular. For bulky cargo, contour approval should therefore be requested at booking stage.

How chargeable weight works

Air freight is charged on the greater of actual gross weight and volumetric weight; the result is the chargeable weight. The IATA standard ratio is 1:6000: length × width × height in centimetres divided by 6,000 gives the volumetric weight in kilograms. The same ratio is often expressed as 1 m³ = 167 kg.

Example: a piece of 120 × 100 × 100 cm weighing 150 kg gross. Volumetric weight is 1,200,000 / 6,000 = 200 kg; as 200 exceeds 150, freight is charged on 200 kg. For cargo with a density below 167 kg/m³ volume drives the price; above it, gross weight does.

Under ULD-based pricing the airline sets a pivot weight for each ULD type: a flat charge applies up to the pivot, and every kilogram above it is charged at a separate over-pivot rate. For dense, regular shipments this model can be cheaper than per-kilogram tariffs.

Practical build-up tips

As a GSSA, Limit Trans verifies the ULD inventory and contour limits of the airlines it represents at booking stage, reducing the risk of cargo being refused at acceptance.

• Place heavy pieces at the bottom and light ones on top; keep the centre of gravity near the middle of the pallet and respect the floor-loading limit (kg/m²).
• Do not let cargo overhang the pallet edge; check the profile with a contour gauge. Anything outside the contour cannot be loaded.
• Secure pallets with nets and straps; fill voids in containers with dunnage so the load cannot shift in flight.
• Keep dangerous goods, live animals and perishables in separate ULDs according to the segregation rules, and keep all labels visible.
• Never use a damaged ULD (cracked panel, bent locking rail); serviceability is checked against the Operational Damage Limits Notice (ODLN).
• Complete the ULD tag with flight number, destination, piece count and weight; this data feeds the load plan and the NOTOC.