Building Air Cargo Pallets: What to Consider Before You Ship

Cargo that arrives at an airport as a stack of individual boxes rarely goes straight onto the aircraft that way. Before loading, much of it is consolidated onto a unit load device — the standardized pallet or container system aircraft holds are built around — so ground crews can move, secure, and load it as one unit rather than many. Getting a pallet build-up right is a detail that's easy to overlook when planning an air freight shipment, but it directly affects whether cargo loads smoothly, whether it fits the aircraft that's been scheduled, and how efficiently it clears each handling step along the way.

This article walks through what a ULD actually is, how a build-up is typically planned and constructed, and the main factors that determine whether a given build-up will work for a specific flight.

What a Unit Load Device Is

A unit load device, commonly abbreviated ULD, is a standardized platform — either a flat pallet with edge rails and netting, or an enclosed container — designed to fit precisely into an aircraft's cargo hold. ULDs come in a range of standardized types, each identified by industry-standard codes, with published base dimensions and maximum gross weight ratings set for each type. Because aircraft holds are physically shaped around specific ULD dimensions, using the correct ULD type for a given aircraft isn't optional — an incompatible ULD simply won't fit into the hold position it's intended for.

ULDs are typically owned or leased by airlines as part of their operating equipment, rather than owned by shippers or forwarders. A shipper's or forwarder's role is to build cargo onto the ULD correctly and hand it over ready for loading — the pallet or container itself is supplied through the airline or the ground handling agent working on the airline's behalf.

Each ULD also has its own tare weight — the weight of the empty pallet or container itself — which matters because it isn't cargo but still counts against the aircraft's total weight capacity for that hold position. A build-up plan that only accounts for the weight of the goods, without adding the ULD's own tare weight, can understate the true weight the aircraft is carrying in that position, which is why the tare weight is a standard figure printed or tagged on the ULD itself and referenced during weight and balance planning.

Why Aircraft Compatibility Matters

Different aircraft models have different hold configurations, and even within a single aircraft type, different hold positions can accept different ULD types. A pallet built up for one aircraft type isn't automatically usable on another — the base dimensions, height contour, and weight limits that apply are specific to the aircraft and hold position the shipment is actually booked to fly on. This is one reason airlines and their handling agents confirm ULD type requirements as part of the booking process rather than leaving it to a shipper's assumption.

Getting this wrong late in the process — building a pallet before confirming which ULD type the confirmed flight requires — can mean a build-up has to be redone, which costs time that's often in short supply for time-sensitive air freight. Confirming ULD type early, ideally at the time of booking, avoids that risk.

Shippers working across multiple airlines or routes sometimes assume ULD requirements are broadly interchangeable because several common ULD types look similar in general shape. In reality, the same-looking pallet type can carry different maximum weight ratings or require different netting configurations depending on which airline's fleet and hold positions it's being loaded into, so confirming requirements with the specific carrier operating a booking — rather than relying on experience from a different airline's equipment — remains the more reliable approach even for shippers who palletize cargo regularly.

Weight Distribution and Structural Limits

An aircraft's cargo hold floor has structural loading limits, and a pallet build-up needs to distribute weight across its base in a way that respects those limits — not just the total weight of the load, but how that weight is spread out. Concentrating heavy pieces in a small area of the pallet base, even if the total weight is within the ULD's overall rating, can exceed the floor-loading limit at that specific point.

Build-up practice generally places heavier, more stable pieces toward the bottom and center of the pallet, with lighter items arranged around and above them, both for structural reasons and to keep the load stable during handling and flight. This is one of the reasons palletization benefits from being planned with knowledge of piece weights and dimensions in advance, rather than stacked ad hoc as pieces happen to arrive at the warehouse.

The ULD's maximum gross weight rating and the floor-loading limits at specific points are two separate checks, and a build-up that passes one doesn't automatically pass the other. A pallet can be well within the ULD's overall weight rating and still fail a floor-loading check if the heavier items are grouped too close together, which is why both figures are checked separately rather than treating total weight as the only number that matters.

Height Contour and Securing the Load

Because aircraft cargo holds are curved to match the fuselage shape, ULDs have an approved height contour that a build-up must stay within — cargo that's stacked too high, or stacked with an uneven profile that pushes past the contour at one edge, won't clear the hold ceiling even if the pallet's base footprint is correct. Contour templates or measuring tools are typically used during build-up to check this before the pallet is finalized.

Once cargo is arranged within the correct footprint and contour, it's secured using a cargo net stretched over the load and locked into the pallet's edge rails, sometimes with corner protectors or additional strapping for particularly heavy or awkwardly shaped pieces. Proper netting is what keeps the load intact through the vibration of ground handling, the acceleration and deceleration of takeoff and landing, and any turbulence encountered in flight — an improperly secured pallet risks cargo shifting, which can damage goods or, in more serious cases, affect aircraft weight and balance.

Before a build-up even begins, the condition of the ULD itself is worth checking, since a damaged pallet base, bent edge rail, or torn net compromises the very structure the load depends on to stay secured. Ground handling agents typically inspect ULDs for damage as part of routine equipment checks, but a shipper or forwarder building cargo onto a pallet at an off-airport warehouse should also look it over before starting, since a damaged unit identified early can be swapped out, while one identified only after build-up means redoing the work.

When Palletization Makes Sense vs. Loose Cargo

Not every shipment needs to be palletized. Smaller shipments, or those that don't fill a meaningful portion of a pallet's base, may be more efficiently handled as loose (bulk) cargo, loaded piece by piece directly into an aircraft's bulk hold — typically found on narrow-body aircraft or in specific hold sections of wider aircraft. Palletization tends to make more sense as shipment volume grows, since consolidating many pieces into fewer handled units reduces the number of individual touches ground crews need to make, which can support faster and more consistent handling.

The choice isn't always the shipper's alone to make — airlines and forwarders assess a shipment's characteristics against the routing and aircraft type booked, and may recommend palletization or bulk handling based on what's most practical for that specific flight and cargo combination.

Documentation follows the same logic as the physical build-up: whichever handling method is used, the shipment's dimensions and weight recorded on the airway bill and other transport documents need to match what's actually tendered to the airline, whether that's a single palletized unit or a set of individual pieces. A mismatch between what's declared and what arrives at the terminal can hold up acceptance regardless of whether the cargo is built onto a pallet or handled loose, so getting piece-level or unit-level figures right matters just as much as the physical handling decision itself.

Some pieces don't lend themselves well to either straightforward palletization or straightforward bulk handling — an odd-shaped machine part or an item that's heavy for its footprint, for instance — and these are usually flagged early so the forwarder and airline can agree on how to handle them rather than discovering the mismatch once the shipment is already at the terminal. Raising unusual piece characteristics at the booking stage, alongside standard dimensions and weights, gives everyone involved time to plan around them properly.