Unit Load Devices, or ULDs, are pallets and containers used to load luggage, freight, and mail on wide-body aircraft. They allow large quantities of cargo to be bundled into large units. Since this leads to fewer units to load, it saves ground crews time and effort, and helps prevent delayed flights. Each ULD is manifested separately so that its contents can be tracked.

Types

ULDs come in two forms: pallets and containers. ULD pallets are rugged sheets of aluminum with rims designed to lock onto cargo net lugs. ULD containers, also known as cans and pods, are fully enclosed containers made of aluminum or combination of aluminum (frame) and plastic (walls) and, depending on the nature of the goods inside, may or may not have refrigeration units built-in. Below are examples of common ULDs and their specifics.

Aircraft Compatibility

LD3s, LD6s, and LD11s will fit 787s, 777s, 747s, MD-11s, L-1011s, and all Airbus wide-bodies. The 767 uses the smaller LD2s and LD8s because of its narrower fuselage. The less common LD1 is designed specifically for the 747, but LD3s are more commonly used in its place because of ubiquity (they have the same floor dimensions so one LD3 takes the place of one LD1). LD7 pallets will fit 7E7s, 777s, 747s, late model 767s (with the big door), and Airbus wide-bodies.

Interchangability of certain ULDs between LD3/6/11 aircrafts and LD2/8 aircrafts is possible when cargo needs to be quickly transferred to a connecting flight. Both LD2s and LD8s can be loaded in LD3/6/11 aircrafts, but at the cost of using internal volume effectively (33 CF wasted per LD2). Only the LD3 of the LD3/6/11 family of ULDs can be loaded in a 767 and will occupy an entire row where two LD2s or one LD8 would have been (90 CF wasted per LD3!). Policies vary from airline to airline whether such transfers are allowed.

One of the design requirements of the 767's replacement, the 7E7, was for it to use the LD3/6/11 family of ULDs to solve the wasted volume issue.

ULD Capacity

Aircraft loadings can be made up of all containers, all pallets, or a mix of ULD types, depending on convenience. Below is a table indicating the maximum capacity of an aircraft for all-container and all-pallet configurations. In some aircrafts the two types must be mixed as some compartments take only certain ULDs.

Container capacity of an aircraft is measured in positions. Each half-width container (LD1s, LD2s, and LD3s) in the aircraft they are native to occupies one position. Typically, each row in a cargo compartment is made of two positions. Therefore, a full-width container (LD6s, LD8s, and LD11s) will take two positions. An LD6 or an LD11 can replace two LD3s. An LD8 replaces two LD2s.

Pallet capacity of an aircraft is measured by how many PMC-type LD7s (96" x 125") it can hold. These pallets use approximately 3 LD3 positions (it occupies 2 positions of one row and half of the 2 the following row) or 4 LD2 positions. PMCs can only be loaded in cargo compartments with large doors designed to accept them (small door compartments are container only).

Identification

All ULDs are identified by their ULD number. A three-letter prefix identifies its type, followed by a 4 or 5 digit serial number to uniquely identify it from others of the same type, and ending with a two character (alpha-numerical) suffix identifying the ULD's owner (if an airline, same as IATA designator codes). For example, AKN 12345 DL means the ULD is a forkliftable LD3 with unique numbers 12345 and its owner is Delta Airlines.

Common Prefixes

• AKN - LD3 container with forklift holes
• AKE - LD3 container with no holes
• RKN - LD3 container with refrigeration unit, same shape as AKE
• DPN - LD2 container with forklift holes
• DPE - LD2 container with no holes
• AKC - LD1 container with no forklift holes
• ALF - LD6 container with no forklift holes
• DQF - LD8 container with forklift holes
• FQA - LD8 pallet (same floor dimensions as DQF)
• ALP - LD11 container with no forklift holes
• AKH, AKW - mainly for A320/321, same base as AKE, extensions on both sides, 45 inches high
• AMU - contour similar to ALF, but deeper and bigger extensions. biggest lower-deck container
• FLA - LD11 pallet
• PLA - LD11 pallet
• PAG, P1P - LD7, large pallet (88" x 125")
• PMC - LD7, large pallet (96" x 125")
• PGE - large pallet, 96 by 238.5 inches. 747 main deck only

First prefix character identifies ULD category (certification, ULD type, thermal units);
second character identifies standard base dimensions;
third identifies contour, forklift holes, and other miscellaneous info. [1]

Miscellaneous Info

• LD3s and LD2s occupy half the width of the cargo bin of the aircraft they are designed for, therefore are loaded two at a time, side-by-side. LD6s and LD8s are, respectively, their full width counterparts and can only be loaded one at a time.
• LD2s and LD8s are ULDs designed specifically for one type of aircraft, the 767. This is because the 767 has a narrower fuselage than other wide-body aircrafts.
• LD1s are ULDs designed specifically for the 747. But LD3s are more commonly used in its place because of ubiquity.
• LD7s inexplicably come in two different floor dimensions.
• Maximum height for all ULDs is 64" for lower deck of aircraft.
• The most common form of ULD damage are holes in container walls from improper forklifting.