Unit Load Device

Unit Load Device

A unit load device, or ULD, is a pallet or container used to load luggage, freight, and mail on wide-body aircraft and specific narrow-body aircraft. It allows a large quantity of cargo to be bundled into a large unit. Since this leads to fewer units to load, it saves ground crews time and effort and helps prevent delayed flights. Each ULD has its own packing list (or "manifest") so that its contents can be tracked as a unit.


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 Lexan (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.

"Pallet volumes shown are built 64 in tall for lower deck loading. Height limit for main deck depends on aircraft type."

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 787s, 777s, 747s, late model 767s (with the big door), and Airbus wide-bodies.

Interchangeability of certain ULDs between LD3/6/11 aircraft and LD2/8 aircraft is possible when cargo needs to be quickly transferred to a connecting flight. Both LD2s and LD8s can be loaded in LD3/6/11 aircraft, but at the cost of using internal volume inefficiently (33 ft³ 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 ft³ 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 787, 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 aircraft 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" × 125") it can hold. These pallets use approximately three LD3 positions (it occupies two positions of one row and half of the two the following row) or four LD2 positions. PMCs can only be loaded in cargo compartments with large doors designed to accept them (small door compartments are container only).

"Maximum capacity shown does not reflect weight restrictions.
Actual number of ULDs loaded may be lower if aircraft is at its weight limit."


All ULDs are identified by their ULD number. A [http://www.fredoniainc.com/glossary/air.html three-letter prefix] identifies its type, followed by a 4 or 5 digit serial number (4 if prior to October 1, 1993; either 4 or 5 if post October 1, 1993) 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, often the 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 Air Lines.

Common prefixes

*AKN: LD3 container with forklift holes
*AKE: LD3 container with no holes
*QKE: LD3 container same as AKE except it is made out of KEVLAR. It is meant to be bombproof. Has no forklift 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
*DQP: LD4 (like an LD8 but without contours)
*FQA: LD8 pallet (same floor dimensions as DQF)
*ALP: LD11 container with no forklift holes
*AKH, AKW: LD3-45 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. freighter 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." [http://www.fredoniainc.com/glossary/air.html]

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 aircraft.
*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.

Main Deck ULDs

On the main deck of cargo planes are tall ULDs (79 to 96 inches tall, 2006mm to 2438mm tall) with foot print dimensions similar to pallets frequently 88 or 96 inches wide (2235mm or 2438mm wide) and 62 or 125 inches long (3175mm long). A 62 x 88 tall ULD is half of 125 x 88 inch pallet. The length is approximately 5 foot for 62 inches, 10 feet for 125 inches. The 20 foot pallet is 238 inches long and 96 inches wide.

There several common types of contoured main deck ULDs, that are contoured (curved to fit in the plane) to provide as much cargo volume as possible. Initially ULD contouring was simply a triangle removed from one or two corners of the profile of the ULD, such as the common LD3 and LD6. Main deck ULDs use curves for the contoured shape to truly maximize cargo volume. Upper deck ULDs are just like lower deck ULDs that are either the full width of the plane with two corners of the profile removed (lower deck LD6 lower, and upper deck AYY), or that container is cut in half, down the center line of the plane, (lower deck LD3 and upper deck AAX).

Main Deck ULDs and pallets are not only taller than lower deck ULDs, they are frequently two or four times longer. They are usually organized like an LD6, using the width of the plane and missing two profile corners, or two very long LD3s, stored in parallel to use the planes width and each missing one profile corner, but often twice or four times as long from planes nose to tail.

Many air cargo companies use main deck ULDs that have both features called dual-profile, so that on small planes such as the Boeing 727, they are stored widthwise and have two corner contoured, and on the bigger Boeing 767, they can be rotated 90 degrees and shipped in parallel like LD3s, so that only one corner is contoured when being used like an LD3. This greatly simplifies transportation of cargo containers at slight cost of cargo volume.

What the actual dimensions of contoured upper deck ULDs are is very hard to know, because most manufacturers only profile width, length and height data.

ee also

* 463L master pallet, used for military airdrops
* Norsk Hydro, parent company of Hydro Nordisk, a manufacturer of ULDs
* Rio Tinto Alcan, formerly Alusuisse, a manufacturer of ULDs


External links

* [http://www.ibafreightservices.com/aircontainers.shtml Air Freight Container Specifications]
* [http://www4.hydro.com/nordisk/en/ Hydro Nordisk] , manufacturer of ULDs
* [http://www.satco-inc.com/ Satco, Inc.] , manufacturer of ULDs

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