Why Air Cargo Gets Offloaded, and How to Avoid It

Air cargo gets offloaded when the airline cannot or will not carry a booked shipment on its planned flight: the aircraft has run out of payload or space, the pieces do not fit the planned unit, or the shipment is not ready to fly because of late delivery, screening, dangerous goods or paperwork problems. Many offloads trace back to one thing: the cargo that arrived is not the cargo that was booked.

This article explains what an offload is, the main reasons, and what shippers and forwarders can do to keep their freight on the flight. Airline rules and priorities vary, so treat the figures here as typical and check your carrier's conditions.

What an offload is

An offload means a shipment booked and accepted for a flight did not travel on it. It can happen at different points:

• At acceptance: the cargo terminal refuses the shipment, or accepts it but marks it not ready for carriage.
• At build-up: the pieces do not fit the planned ULD, or the build goes over its weight or contour.
• At final load planning: the load controller removes units or bulk cargo to meet payload or balance limits.
• On the ramp: a ULD is pulled at the aircraft because it will not fit the position or the flight is closing.

An offloaded shipment is normally rebooked on the next available flight. For general cargo that can mean a day or more; for perishables, pharma or production parts, the delay can cost far more than the freight.

The main reasons at a glance

Payload and weight-and-balance limits

The cargo an aircraft can take is what is left after fuel, passengers, bags and crew. That figure changes from flight to flight. Strong headwinds need more fuel, hot days and short or high runways reduce take-off weight, and a full passenger load leaves less for cargo in the belly.

The load controller also has to keep the aircraft's centre of gravity within limits and stay within the limits for each hold and position. A heavy ULD that would only fit at the end of the hold may be swapped for a lighter one, even if the total weight is fine. Offloads for these reasons often happen late, when final passenger and fuel figures come in.

Shippers cannot change the aircraft's limits, but they can make sure the weight they declared is the weight that arrives. A pallet 20% heavier than booked is the obvious one to pull.

Volume and the ULD contour

In practice, space usually runs out before weight on many flights, especially for light, bulky cargo. Space is not only cubic metres. Each aircraft position has a contour: the outline a built ULD must stay within to pass the door and fit the fuselage. On a typical wide-body lower deck, the build height is about 160 cm. Main-deck positions on freighters allow much more, with height and shape varying by position.

So a shipment can be offloaded even when the booked volume is free:

• A piece of 170 cm height cannot go in a lower-deck position, so it needs a main-deck position, which a passenger flight does not have.
• A long piece cannot turn through the cargo door even though the hold is long enough.
• A pallet built to its full footprint at the base cannot be stepped in at the top corners to meet a sloped contour.
• Pieces that cannot be stacked waste the height above them, so the unit is full by volume before the booked cubic metres are used.

Piece size limits by aircraft type are covered in maximum cargo size for air freight, and how handlers build to the contour in ULD build-up.

Late tender

Each flight has a latest acceptance time (LAT): the latest the cargo can be handed over at the terminal and still be screened, built up and loaded. Typical LATs are several hours before departure, longer for dangerous goods, special cargo and freighter flights. Cargo that arrives after the LAT is often accepted but not loaded, which shows in tracking as an offload.

A truck stuck in traffic, a queue at the terminal or a delivery slot missed by 30 minutes is enough. Build the LAT into the trucking plan with a margin, not as the target arrival time.

Security screening

Air cargo must either come from a secure supply chain or be screened before loading. In the EU this is set out in Regulation (EU) 2015/1998, with known consignors and regulated agents; in the United States, the TSA requires all cargo on passenger aircraft to be screened. Cargo that is not secured has to be screened at the terminal, by X-ray, explosive trace detection, sniffer dogs or physical search. Large, dense or mixed pieces can be hard to screen, and screening capacity is limited at peak times.

Advance data rules add another check. Under the EU's ICS2, the shipment data must be filed before loading, and a 'do not load' message from customs stops the cargo until it is resolved. The US has a similar pre-loading programme (ACAS). Missing or poor data, such as a vague goods description, is a common cause.

Dangerous goods and documents

Dangerous goods are checked at acceptance against the IATA Dangerous Goods Regulations. Common problems:

• The Shipper's Declaration for Dangerous Goods does not match the packages, or is missing details.
• Wrong or missing labels and marks, or a damaged or leaking package.
• Cargo Aircraft Only packages booked on a passenger flight.
• Lithium batteries shipped without the right marks or not declared at all.

Other documents cause offloads too: an air waybill with a piece count or weight that does not match the cargo, missing export declarations, or missing permits for controlled goods. If the cargo terminal finds 12 pieces on an air waybill for 10, the shipment waits until the discrepancy is cleared.

Priority cargo and aircraft changes

When space is short, airlines decide what flies. Many carry mail under contract, and express, perishables, pharma, live animals and higher-yield bookings often have priority over general cargo on deferred rates. The exact order is each airline's commercial choice, and it is often written into the rate or product conditions.

Airlines also swap aircraft for operational reasons. A wide-body replaced by a narrow-body can lose most of its ULD capacity, and a freighter replaced by a passenger aircraft loses the main deck. Shipments planned for the original aircraft are then rebooked.

Booked versus actual: a worked example

A forwarder books 6 pallets of machine parts on a passenger flight with a wide-body lower deck.

1. 1Booked: 6 pallets of 120 × 80 × 150 cm, 300 kg each. Volume: 6 × 1.44 = 8.64 m³. Volume weight at 6,000 cm³ per kg: 8,640,000 ÷ 6,000 = 1,440 kg. Actual weight 1,800 kg. Chargeable weight 1,800 kg.
2. 2Arrives: 6 pallets of 120 × 100 × 170 cm, 330 kg each. Volume: 6 × 2.04 = 12.24 m³, 42% more than booked. Volume weight: 2,040 kg. Actual weight 1,980 kg. Chargeable weight 2,040 kg.
3. 3Height: 170 cm is above the typical 160 cm lower-deck build height. These pallets cannot go in a lower-deck position at all.
4. 4Result: the shipment is offloaded and rebooked on a freighter, days later, and invoiced at the higher chargeable weight.

Had the pallets been built to 150 cm as booked, with the extra goods on a seventh pallet, the shipment would most likely have flown. Use the chargeable weight calculator to check the figures before booking, and see air cargo chargeable weight for the rules.

What shippers and forwarders can do

1. 1Measure and weigh every piece before booking. Book the real dimensions and weights, including the pallet and packaging, not estimates from the order.
2. 2Check piece sizes against the aircraft. Know whether the flight is lower deck only or has a main deck, and check the door and contour for tall or long pieces.
3. 3Build to the booked height. If the booking says 150 cm, the warehouse must build to 150 cm. Give them the limit in writing.
4. 4Pre-plan the ULD build for full-unit bookings, so you know the cargo fits the unit and contour before it reaches the terminal.
5. 5Know the chargeable weight. Light, bulky cargo is charged by volume and also takes the space airlines run out of first. Denser packing helps on both counts.
6. 6Deliver well before the LAT, and use a secure supply chain (known consignor or regulated agent) so the cargo does not wait for screening.
7. 7Get dangerous goods right first time. Trained staff, correct declaration, labels and packaging, and the right aircraft type.
8. 8Send complete data early: air waybill, goods description, and advance customs data.
9. 9Ask about priority. For urgent cargo, a priority product or guaranteed capacity can cost less than a missed connection.

For packaging that handles well and fits units cleanly, see packing for air freight.

Plan ULD builds in EveryLoading

Before the cargo leaves the warehouse, check it against the unit it is booked on. The air cargo planner shows how it fits, and ULD types explained gives the unit sizes.