A unit load device (ULD) is a container used to load luggage, freight, and mail on wide-body aircraft and specific narrow-body aircraft. It allows preloading of cargo, provided the containerised load fits in the aircraft, enabling efficient planning of aircraft weight and balance and reduced labour and time in loading aircraft holds compared with 'bulk-loading' single items of cargo or luggage by hand. Each ULD has its own packing list or manifest so that its contents can be tracked. A loaded aircraft cargo pallet secured with a cargo net also forms a ULD, but its load must be gauged for size in addition to being weighed to ensure aircraft door and hold clearances.
The IATA publishes ULD regulations and notes there are 900,000 in service worth more than US$1 billion, averaging $ each.[1]
ULDs come in two forms: pallets and containers. ULD pallets are rugged sheets of aluminium with rims designed to lock onto cargo net lugs. ULD containers, also known as cans and pods, are closed containers often made of aluminium or a combination of aluminium (frame) and Lexan (walls) but there are examples of containers made of GRP with an insulating foam core. Depending on the nature of the goods to be transported, ULDs may have built-in refrigeration units. Examples of common ULDs and their specifics are listed below.
| Type | Internal volume | Height | Depth | Width | Contour | IATA | Suitability | ||
|---|---|---|---|---|---|---|---|---|---|
| Base | Overall | Nominal | |||||||
| LD3-45[3] | Full | Double | AKH | Airbus A319/Airbus A320/Airbus A321 | |||||
| LD2 | Half | Single | APE | Boeing widebodies | |||||
| LD3 | AKE | Airbus and Boeing widebodies, DC-10/MD-11, L-1011 | |||||||
| LD1 | AKC | Boeing widebodies, MD-11 | |||||||
| LD4 | Full | None | AQP | Boeing 767/777/787 | |||||
| LD8 (2×LD2) | Double | AQF | Boeing 767/787 | ||||||
| LD11 | None | ALP | Boeing 747, 777, 787, DC-10/MD-11 | ||||||
| PLA pallet | PLA | 747, 777, 787 | |||||||
| LD6 (2×LD3) | Double | ALF | 747/777/787, DC-10/MD-11 | ||||||
| LD26 (P1P base) | AAF | Airbus A330, A340, A350, and Boeing 747/777/787, DC-10/MD-11 | |||||||
| LD7 winged pallet | P1P | 747, 777, 787, DC-10/MD-11 | |||||||
| LD7/P1P pallet | None | P1P | All widebodies | ||||||
| LD9 (P1P base) | AAP | Boeing widebodies, DC-10/MD-11 | |||||||
| LD29 (P1P base) | Double | AAU | 747 | ||||||
| LD39 (P6P base) | AMU | 747 | |||||||
| P6P pallet | None | P6P | 747, 767, 777, 787, DC-10, MD-11 | ||||||
LD3s, LD6s, and LD11s will fit 787s, 777s, 747s, MD-11s, Il-86s, Il-96s, 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 such that one LD3 takes the place of one LD1). LD3s with reduced height (452NaN2 instead of 642NaN2) can also be loaded on the Airbus A320 family. LD7 pallets will fit 787s, 777s, 747s, late model 767s (with larger doors), 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; it will occupy an entire row where two LD2s or one LD8 would otherwise have fit (90 ft3 wasted per LD3). Policies vary from airline to airline as to whether such transfers are allowed.
The 787, intended to replace the 767, was designed to use the LD3/6/11 family of ULDs to solve the wasted volume issue.[4]
| Lower deck ! | Main deck | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| data-sort-type="number" | Containers ! | data-sort-type="number" | 88×125″ ! | data-sort-type="number" | 96×125″ | data-sort-type="number" | 96×125″ ! | data-sort-type="number" | 88×125″ ! | data-sort-type="number" | 88x108″ |
| Airbus A300-600[5] | data-sort-value="4.10" | 4 + 10 LD3 | data-sort-value="4.10" | 4 + 10 LD3 | 20 | 21 | |||||
| Airbus A310[6] | LD3 | data-sort-value="3.07" | 3 + 7 LD3 | data-sort-value="3.07" | 3 + 7 LD3 | 15 | 16[7] | ||||
| Airbus A330-2/800[8] | LD3 | ||||||||||
| Airbus A330-3/900 | LD3 | 26 | 26[9] | ||||||||
| Airbus A340-200[10] | LD3 | ||||||||||
| Airbus A340-300 | LD3 | ||||||||||
| Airbus A340-500[11] | LD3 | ||||||||||
| Airbus A340-600 | LD3 | ||||||||||
| Airbus A350-900[12] | LD3 | ||||||||||
| Airbus A350F[13] | 40 LD3 | 12 | 30 | ||||||||
| Airbus A350-1000 | LD3 | ||||||||||
| Airbus A380-800[14] | LD3 | ||||||||||
| Boeing 747 classic[15] | data-sort-value="33" | 28 | 28 | 36 | |||||||
| Boeing 747SP | data-sort-value="22" | ||||||||||
| Boeing 747-400[16] | data-sort-value="35.2" | data-sort-value="9.044" | 9 + 4 LD1 | data-sort-value="9.022" | 9 + 2 LD1 | 30 | 30 | ||||
| Boeing 747-8/8F[17] | data-sort-value="44" | data-sort-value="12.022" | 12 + 2 LD1 | ||||||||
| Boeing 767-200[18] | data-sort-value="17.2" | data-sort-value="3.078" | 3 + 10 LD2 | data-sort-value="3.078" | 3 + 10 LD2 | ||||||
| Boeing 767-300 | data-sort-value="23.4" | data-sort-value="4.1092" | 4 + 14 LD2 | data-sort-value="4.1092" | 4 + 14 LD2 | 14 | |||||
| Boeing 767-400 | data-sort-value="29.6" | 5 + 16 LD2 | |||||||||
| Boeing 777-200[19] | LD3 | data-sort-value="10.02" | + 2 LD3 | 27 | |||||||
| Boeing 777-300 | LD3 | data-sort-value="14.02" | + 2LD3 | 33[20] | |||||||
| Boeing 777-8F[21] | 40 LD3[22] | 13 | 31 | ||||||||
| Boeing 777-9[23] | LD3 | data-sort-value="14.04" | + 4 LD3 | ||||||||
| Boeing 787-8[24] | LD3 | data-sort-value="8.02" | + 2 LD3 | ||||||||
| Boeing 787-9 | LD3 | ||||||||||
| Boeing 787-10 | LD3 | ||||||||||
| Douglas DC-10[25] | LD3 | data-sort-value="5.08" | 5 + 8 LD3 | 22 | 30 | ||||||
| McDonnell Douglas MD-11[26] | LD3 | data-sort-value="6.14" | 6 + 14 LD3 | 26 | 26 | 34 | |||||
| Lockheed L-1011[27] | LD3 | data-sort-value="4.07" | 4 + 7 LD3 | ||||||||
| Ilyushin Il-86/Il-96-300[28] | 16 LD3 | ||||||||||
| Ilyushin Il-96M/T[29] | 32 LD3 | ||||||||||
| Model | data-sort-type="number" | Containers ! | data-sort-type="number" | 96×125″ ! | data-sort-type="number" | 88×125″ ! | data-sort-type="number" | 88x108″ |
|---|---|---|---|---|---|---|---|---|
| Airbus A319[30] | ||||||||
| Airbus A320[31] | LD3-45 | 11[32] | ||||||
| Airbus A321[33] | LD3-45 | 14 | ||||||
| Boeing 707-320C[34] | no lower ULD | 13 | 13 | |||||
| Boeing 727-100C[35] | no lower ULD | 8 | 8 | |||||
| Boeing 737-200C[36] | no lower ULD | 7 | 7 | |||||
| Boeing 737-300SF[37] | no lower ULD | 9 | ||||||
| Boeing 737-400SF[38] | no lower ULD | data-sort-value="10.5" | 10 ½ | |||||
| Boeing 737-700C | no lower ULD | 8 | 8 | |||||
| Boeing 737-800SF[39] | no lower ULD | data-sort-value="11.5" | 11 ½ | |||||
| Boeing 757-200F[40] | no lower ULD | 15 | ||||||
| Douglas DC-8-55F[41] | no lower ULD | 13 | ||||||
| Douglas DC-8-62/72F | no lower ULD | 14 | ||||||
| Douglas DC-8-61/63/71/73F | no lower ULD | 18 | ||||||
| Douglas DC-9-15F[42] | no lower ULD | 6 | ||||||
| Douglas DC-9-32F | no lower ULD | 8 | ||||||
| McDonnell Douglas MD-80SF[43] | no lower ULD | 8 | 8 | 12 |
Aircraft loads can consist of containers, pallets, or a mix of ULD types, depending on requirements. In some aircraft the two types must be mixed as some compartments take only specific ULDs.
Container capacity of an aircraft is measured in positions. Each half-width container (LD1/LD2/LD3) in the aircraft it was designed for occupies one position. Typically, each row in a cargo compartment consists of two positions. Therefore, a full-width container (LD6/LD8/LD11) will take two positions. An LD6 or an LD11 can occupy the space of two LD3s. An LD8 takes the space of two LD2s.
Aircraft pallet capacity is measured by how many PMC-type LD7s can be stored. These pallets occupy approximately three LD3 positions (two positions of one row and half of the two positions of 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).
| Model | LD3 | 46×66” | 88×54” | 88×62” | 88×108” | 96×125” | |
|---|---|---|---|---|---|---|---|
| Fokker 100[44] | 11 | ||||||
| CRJ200[45] | 8 | ||||||
| BAe 146-200[46] | 9 | 6 | 4 | ||||
| ATR 72[47] | 7 | 9 | 5 | ||||
| 5 | 6 | 3 | |||||
| Dash 8-300[48] | 9 | ||||||
| Xian MA600[49] | 5 | 5 | |||||
| Short 360[50] | 5 | ||||||
| Cessna SkyCourier[51] | 3 |
All ULDs are identified by their ULD number. A three-letter prefix identifies its type and key characteristics,[52] followed by a 4 or 5 digit serial number (4 if prior to October 1, 1993; either 4 or 5 if after 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 that the ULD is a forkliftable LD3 with the unique number 12345 and its owner is Delta Air Lines.[53]
On the main deck of cargo planes are 79to tall ULDs with footprints similar to those of 88inches or 96inches wide pallets and 62inches or 125inches long. A 620NaN0 wide × 880NaN0 tall ULD is half the volume of a 1250NaN0 × 88 inch pallet. The 20 foot pallet is 238inches long and 96inches wide. 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.
There are several common types of contoured main deck ULDs, that are contoured (curved to fit in the plane's body) 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), 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 plane's width and each missing one profile corner, but often twice or four times as long from plane's nose to tail.
Many air cargo companies use main deck ULDs that have both features called dual-profile, so that on smaller planes such as the Boeing 727, they are stored widthwise and have two corners 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.