Air freight containers are essential components of modern air cargo logistics. Each year, millions of tons of goods move across global air networks packed into standardized air freight containers. Also known as Unit Load Devices (ULDs), these containers enable efficient, secure, and cost-effective transport of cargo in aircraft holds.
For importers, understanding the types, sizes, and specifications of air freight shipping containers offers practical benefits. While container selection is typically handled by the carrier or freight forwarder, being informed about these details can improve communication, support more accurate load planning, and help prevent shipment delays.
In this article, we will discuss air freight containers and the essential details you need to know as an importer or business owner to navigate the air cargo process with confidence and clarity. We’ll also look at how digital freight forwarders like Ship4wd can help you streamline shipping with both air and ocean freight options, along with value-added services that support smoother operations and greater supply chain efficiency.
Air Freight Containers: What Is a Unit Load Device (ULD)?
Let’s start from the basics: Unit Load Devices are standardized containers or pallets used to load freight, baggage, and mail onto aircraft. These air freight containers are designed to fit the contours of an aircraft’s hold, enabling efficient use of space while protecting cargo during transport.
Unlike ocean shipping containers, which are large, rigid metal boxes, ULDs are lightweight and built specifically for air transport. They are secured within the aircraft and must meet strict safety and handling requirements set by the International Air Transport Association (IATA).
ULDs come in two main forms, each serving a different purpose in air cargo transport:
- Pallets: Flat bases where cargo is securely strapped and netted — ideal for large, heavy, or irregularly shaped shipments.
- Containers: Enclosed units that offer added protection, especially for delicate or high-value goods.
In the next section, we’ll take a closer look at these different air freight container types and how they’re used.
By understanding the role ULDs play in air freight logistics, you’ll gain valuable insight into how your cargo is loaded, moved, and safeguarded throughout its journey. With this knowledge, you can better plan your shipments and avoid costly surprises.
ULD Benefits for Importers
Using air freight containers offers several key advantages that directly impact your shipping efficiency and cargo safety:
- Faster Ground Handling: ULDs enable quicker loading and unloading of aircraft, reducing ground time and helping to keep your shipments moving on schedule.
- Damage Protection: Cargo packed in air freight containers is better protected from handling damage, weather, and other external risks compared to loose or unprotected shipments.
- Airline Compatibility and Space Maximization: Standardized ULDs are designed to fit the specific dimensions of aircraft holds. This ensures optimal use of available space and improves cargo capacity planning for airlines and freight partners.
- Enhanced Cargo Security: Sealed air freight containers help reduce the risk of theft and tampering during transit, providing an added layer of security for high-value or sensitive goods.
Common ULD Types and What They Fit
ULD codes look cryptic, but each one tells you exactly what shape, size, and aircraft position you’re working with.
The LD3, coded AKE, is the workhorse of the industry: a contoured lower-deck container holding around 4.5 cubic meters, and it fits the belly hold of nearly every wide-body passenger and freighter aircraft in service, from the 767 and 777 to the A330 and A350. The PMC pallet is a flat main-deck unit used on larger freighters like the 747 and A380, built for oversized or irregularly shaped cargo that a rigid container can’t accommodate. The LD7 is a similar main-deck container option where enclosed protection matters more than netting flexibility. Specialty variants exist too, including RKN containers with active cooling for pharmaceuticals and temperature-sensitive goods, and fire-resistant units built specifically for lithium battery shipments.
Your freight forwarder or airline selects the exact ULD based on your cargo’s dimensions and the aircraft flying your route, but knowing the names helps you understand why a quote changes when your shipment’s size or weight crosses a threshold.
ULD Dimensions and Weight Limits at a Glance
| ULD Type | IATA Code | Typical Volume | Best For |
|---|---|---|---|
| LD3 (lower-deck container) | AKE | Approx. 4.5 cbm | General cargo on most wide-body aircraft |
| LD7 (main-deck container) | – | Approx. 10 cbm or more | Larger shipments transported on the main deck of aircraft such as the Boeing 747 or Airbus A380 |
| PMC pallet | – | Varies by build | Oversized or irregularly shaped cargo |
| RKN (active cooling container) | – | Approx. 5–6 cbm | Pharmaceuticals and other temperature-sensitive goods |
These figures vary somewhat by manufacturer and airline, so always confirm exact dimensions and weight limits with your freight forwarder or the operating airline before finalizing packaging for a shipment that’s tight against a size or weight threshold.
Types of Air Freight Containers
Before diving into specific ULD types, it’s important to understand the two main categories used in air freight.
The first is pallet-based ULDs, which are flat aluminum bases equipped with foldable side wings and cargo netting. These are typically used for heavy, oversized, or irregularly shaped goods that require flexible handling and secure strapping during transport.
The second category is container-based ULDs. These are fully enclosed units, often contoured to match the shape of an aircraft’s hold. Their design helps protect cargo from environmental exposure and handling damage while maximizing the available space inside the aircraft. Container-based ULDs are commonly used for general cargo, high-value goods, and temperature-sensitive shipments.
All ULDs are built according to strict IATA standards, ensuring consistent compatibility across different airlines and aircraft types. Each ULD is classified using specific IATA/ATA codes, such as AKE, AME, or RKN, which indicate the unit’s size, shape, and any special features like insulation or refrigeration.
Container‑Based ULDs
These sealed, rigid air freight containers are precisely shaped for aircraft lower holds, ensuring secure loading and protection:
- LD‑1 (AKE/AKC): Half-width lower-hold container for Boeing 747/767/777/787 and MD‑11. Max gross: 1,588 kg; Tare: 70–170 kg; Volume: 5 m³; Door opening: 147 × 155 cm.
- LD‑2 (DPE): Smaller half-width lower-hold container suitable for the same aircraft. Max gross: 1,225 kg; Tare: 92 kg; Volume: 3.5 m³; Door opening: 112 × 152 cm.
- LD‑3 (AKE): Most common half-width container for wide-bodies. Max gross: 1,588 kg; Tare: 82 kg; Volume: 4.5 m³; Door opening: 147 × 155 cm.
- LD‑6 (ALF): Full-width, contoured lower-hold container. Max gross: 3,175 kg; Tare: 230 kg; Volume: 9.1 m³.
- LD‑11 (ALP): Full-width rectangular container. Max gross: 3,176 kg; Tare: 185kg; Volume: 7.4 m³.
- LD‑26 (AAF): Full-width contoured container on a P1P base. Max gross: 6,033 kg; Tare: 250 kg; Volume: 13.3 m³.
- LD‑29 (AAU): Slightly larger version of the LD‑26, also on a P1P base. Max gross: 6,033 kg; Tare: 265 kg; Volume: 14.4 m³.
Insulated / refrigerated variants:
Certain ULDs include built-in insulation or active cooling systems to maintain temperature-sensitive cargo during transport. These are certified to precise IATA and Boeing standards:
- RKN (insulated LD‑3): Based on the half-width LD‑3 (AKE), the RKN is a temperature-controlled container that adds thermal insulation. It meets Type 8 classification and typically offers an internal volume of 4.5 m³ (159 ft³) with a maximum gross weight of 1,588 kg. Depending on the model, tare weight ranges from around 210 kg to 635 kg, and many units can maintain 0–25 °C for up to 30 hours.
- RAP (Envirotainer RAP e2): The RAP, based on an enclosed LD-9 unit mounted on a P1P pallet, provides active refrigeration suitable for long-duration temperature-controlled shipments. External dimensions are 3,175 × 2,235 × 1,626 mm, with internal space of 2,465 × 2,055 × 1,260 mm. Tare weight is around 400–462 kg; max gross weight is 6,000 kg (lower deck). Internal volume is approximately 9.6 m³ (339 ft³), and the unit autonomously maintains temperature for at least 30 hours.
Pallet‑Based ULDs
Pallet-based ULDs consist of flat aluminum sheets with fold-down wings and cargo nets, making them ideal for loading irregular or heavy freight. They comply with IATA specifications and fit securely into both main and lower deck aircraft compartments.
- 88‑in pallet (P1P): Base size: 88 × 125 in (223 × 317 cm); tare ~114 kg; max gross 4,626 kg (lower deck), up to 6,033 kg (main deck); volume ~14 m³. IATA/AS1825 code P1P/PAG; used on A300/A310/A340, 747, 767, 777 in both lower and main decks.
- 96‑in pallet (PMC/P6P): Base: 96 × 125 in (244 × 317 cm); tare ~120 kg; max gross 6,804 kg (main deck), 5,035 kg (lower deck); volume ~11.5 m³. Coded P6P/PMC; standard pallet for 747, 767, 777, 787, MD‑11 freighters and passenger aircraft.
- Half‑pallet (PNA/PLA): Base: 64 × 125 in (162 × 317 cm); tare ~100 kg; max gross 3,175 kg; volume ~7.1 m³. Used for lower-deck shipments on wide-body jets.
- 16‑ft pallet (PRA): Base: 96 × 196 in (244 × 498 cm); tare ~410–470 kg; max gross 11,300 kg; volume ~27.6 m³. Designed for oversized loads (e.g., vehicles) on main decks of 747F, combi, and 777F.
- 20‑ft pallet (PGA): Base: 96 × 238 in (244 × 606 cm); tare ~500–565 kg; max gross 11,340 kg (≈25,000 lb); volume ~33.7 m³. Fits main decks of 747F, 747 Combi, and 777F – ideal for long/heavy cargo.
Special‑Purpose & Smart ULDs
Special-purpose and smart ULDs are designed for sensitive, high-value, or temperature-controlled cargo. They provide enhanced protection, precise temperature management, and real-time tracking throughout the air freight process:
Temperature-Controlled (Insulated/Reefer) ULDs
- RKN (Insulated LD‑3): IATA code RKN, based on the half-width LD‑3. External dimensions are ≈ 200 × 154 × 162 cm; internal ≈ 134 × 131 × 131 cm. Tare is ~210 kg, max gross 1,588 kg, volume ~3.1 m³. It passively maintains 0–25 °C for ~30 hours, suitable for pharmaceuticals and perishables.
- RAP (Insulated LD‑9 Reefer): Code RAP corresponds to an insulated container on a P1P pallet base. Door opening is 216 × 147 cm; tare ~400 kg, max gross 4,626 kg (lower deck). Internal volume is ~9.6 m³, with passive temperature control, making it ideal for large volume temperature-sensitive cargo
High-Capacity/Main Deck Boxes
- 20-ft Container (AGA code): Main-deck ULD with solid door. External dims ≈ 606 × 244 cm; tare ~1,000 kg, max gross 11,340 kg; volume ~33.7 m³. Commonly used on freighters like the 747F/777F for heavy, large shipments.
IoT‑Enabled (Smart) ULDs
- IATA’s ULDR highlights “smart ULD radar,” capable of tracking temperature, location, door status, and tilt through IoT sensors. These ULDs connect with airline and ground systems to provide full visibility and automated alerts.
Why This Technical Depth Matters for Importers
- Accurate Load Planning: Knowing ULD volumes and weight limits helps you calculate exactly how much cargo to pack.
- Cargo Fit and Compatibility: Prevents delays or rework due to mismatched container or aircraft restrictions.
- Specialized Shipping Options: Perishable, and high-value shipments often require temperature control and advanced tracking.
Preparing Cargo for Air Freight: How Cargo Gets to the Plane
Many importers wonder who actually decides which air freight container or ULD will be used for their shipment. In reality, this choice is made by the airline and the freight forwarder, who select the appropriate container based on factors like the size and nature of the cargo, total shipment volume, the type of aircraft, and which ULDs are available at the time. While you won’t select the container yourself, understanding how this process works can help you prepare your cargo correctly and avoid potential issues during loading.
Cargo Flow: From Supplier to Aircraft
- Pickup and Delivery: Your goods are first picked up from your supplier and transported either to a temporary facility or directly to the airport cargo terminal.
- Inspection and Consolidation: At the terminal or facility, cargo is inspected, documented, and, if necessary, consolidated with other shipments to optimize ULD loading.
- ULD Loading: Cargo is carefully loaded into pre-selected air freight containers or prepared on pallet-based ULDs, following precise weight and balance requirements.
- Ground Handling and Aircraft Loading: ULDs are moved using specialized ground equipment and secured within the aircraft hold, ensuring compliance with the aircraft’s configuration and safety protocols.
Air Freight Packaging and Compliance
Proper packaging is essential for a smooth air freight process:
- Shipments must comply with airline rules for size, weight, labeling, and materials.
- Airlines strictly enforce these regulations and will reject any non-compliant cargo, causing delays and potential extra costs for the shipper.
- Certain goods, such as hazardous materials, require additional certifications and packaging controls.
You can find more information about packaging for air freight shipments in our dedicated guide.
How Pre-Shipment Inspections Reduce Risk
To help your air shipments go smoothly, Ship4wd offers pre-shipment inspections as an added-value service within our freight forwarding solution. These inspections help ensure your cargo is fully prepared for air transport before it reaches the terminal:
- Our inspectors examine packaging and labeling to confirm they meet physical shipping and regulatory standards.
- They measure cargo dimensions and weight to verify compatibility with air freight requirements.
- They assess product quality, materials, appearance, and functionality to ensure your order meets expectations.
- They flag any issues early to help you avoid airport rejections, customs delays, or last-minute rework.
By identifying potential problems before departure, you can streamline your shipping process and reduce the risk of costly disruptions.
Ship4wd: Streamline Your Air Freight Shipping with End-to-End Support
Understanding how air freight containers work is just the beginning. When you’re ready to ship, Ship4wd provides the tools and support to manage every stage of your international shipping logistics, whether you’re moving goods by air or sea.
From pickup to delivery, we help you coordinate across suppliers and carriers in different countries. With a reliable partner by your side, you can navigate air freight with greater clarity, compliance, and confidence.
Using our platform, you can instantly quote and book international air freight and ocean freight services, including both FCL (Full Container Load) and LCL (Less than Container Load) shipments.
We also offer cargo insurance, pre-shipment inspections, and advanced tracking tools to give you visibility across your supply chain.
Furthermore, we manage the customs clearance process and submit the required documentation on your behalf to facilitate a smooth transition through customs.
Our 24/7 customer support team is here to answer your questions, assist with tracking, and help you navigate our user-friendly platform.
Sign up with Ship4wd today to simplify your imports with the help of a trusted shipping partner.