Disclaimer — This article is provided as general logistics industry knowledge and practical reference only. It does not constitute aviation safety, dangerous goods carriage, legal, tax or other professional advice. Actual transport, declaration, packaging, loading and customs requirements are subject to the carrier, competent authorities, official regulations and professional advice.
Heavy cargo in air transport isn’t simply a matter of “as long as the total weight isn’t exceeded, it can fly.”A 5-metric-ton piece of equipment, if its weight is concentrated on four small support legs, can be more dangerous than a shipment of 10 metric tons of evenly distributed box cargo. What really matters for heavy air cargo is how the weight is distributed across the aircraft floor and the ULD. The value of a load-spreading pad lies in distributing point loads across a larger surface area.
Schematic of a pad for heavy air cargo
Why Floor Load Capacity Matters for Heavy Cargo
An aircraft cargo hold floor is not an infinitely sturdy platform. Each area has load limits, including not only total weight but also concepts such as load per unit area, line load, and point load. If the contact area of heavy cargo is too small, it may exceed the load-bearing capacity of the local structure.
Concepts
Simple Explanation
Total Weight
How much does this shipment weigh in total?
Point Load
Weight concentrated at a small contact point
Area load
Weight distributed over a larger area
Line load
Weight distributed along a line
Support plate
Using wooden or metal plates to increase the load-bearing area
Customers often say, “This shipment is only 3 metric tons—it’s not heavy.” However, if 3 metric tons are concentrated on four very small metal feet, the localized pressure can be extremely high.
What problem do shims solve?
The purpose of shims is to distribute the weight of the cargo over a larger contact area, thereby reducing the pressure per unit area.
Without Spacers
With shims
Weight concentrated on the support legs
Weight distributed across the pads
Prone to exceeding point load limits
More likely to meet floor load limits
May damage the ULD or floor
Protects pallets and aircraft structure
Fewer attachment points
Facilitates lashing and stabilization
A dunnage block is not just any random piece of wood. Factors to consider include material strength, dimensions, thickness, the structure of the cargo’s base, center of gravity, direction of force, and slip resistance.
Simplified Calculation Approach
Actual engineering calculations must be verified by professionals and the airline, but freight forwarders can understand the basic logic:
``text 单位面积压力 = 货物重量 / 实际接触面积 ``
If the contact area is too small, use dunnage to increase it.
Scenarios
Assessment
Very small feet
High risk; shims required
Base covers the entire surface
Lower risk, but still depends on the weight
Center of gravity is off-center
Consider using a support board to account for uneven load distribution
Cargo may vibrate
Anti-slip measures and securing are required
The bottom of the packaging is fragile
Padding may protect the packaging
If the customer can provide base drawings, leg dimensions, and the center of gravity, the airline’s assessment process will be much faster.
Heavy Cargo Information Checklist
Information
Purpose
Weight per Piece
Load Assessment
Base Contact Area
Calculated Pressure
Number and Dimensions of Support Feet
Determining point load
Center of gravity
Determining force distribution
Packaging base structure
Determining Whether a Spacer Is Needed
Lifting/Forklift Handling Methods
Determining whether ground handling is required
Can it be tilted?
Determine the loading path
Do not rely on verbal estimates for this type of data. For machinery, molds, engines, transformers, and pump and valve equipment, it is best to provide drawings.
How to Design Shims
Design Considerations
Notes
Area
Sufficient to distribute the weight
Thickness
Sufficient to resist bending and compression
Material
Meets strength and quarantine requirements
Non-slip
Prevents shifting during transport
Position
Aligned with load-bearing points and floor structure
Securing
Follow the same securing logic as for the cargo and ULD
For wooden pallets, also consider the destination country’s requirements for wooden packaging. Do not use non-compliant wood as temporary padding under cargo, as this may cause customs clearance and quarantine issues.
Loading Procedure for Heavy Cargo
Stage
Action
Key Points
1. Cargo Profile
Weight, Base, Center of Gravity
Don’t just look at the total weight
2. Load Assessment
Airlines/GHA determine floor and ULD
Data Required
3. Pad Solutions
Design dimensions, materials, and placement
To be confirmed
4. Ground Equipment
Forklifts, cranes, high-lift trucks
Can they be moved safely?
5. Securing with Plywood
Lashing, anti-slip measures, center of gravity
Preventing Displacement
6. Loading and Leveling
Compartment placement, weight distribution
Airline control
For heavy cargo shipments, it’s best to avoid rushing to meet the cut-off time. If any step—such as dunnage, slinging, or securing—is done on the fly, problems are likely to arise.
How OneCargoKit Can Help
Billing for heavy cargo and loading are two separate processes. Initially, use the Chargeable Weight Calculator to determine the billable weight, then use the ULD Calculator to perform a preliminary screening for dimensional compatibility.
However, floor load capacity and dunnage plans must be verified by the airline or professional engineers; online tools cannot replace load engineering.
Common Misconceptions
Misconception 1: If the total weight is within limits, individual pieces must be fine.
The point load of a single piece may exceed the limit.
Misconception 2: The larger the dunnage, the better.
It also depends on the material, thickness, location, and available space.
Misconception 3: A wooden crate base is the same as a support pad.
A wooden crate’s base may not necessarily distribute the load effectively.
Misconception 4: Temporary shims can be used at the airport.
Temporary pallets may not meet strength and quarantine requirements.
Misconception 5: Heavy cargo only affects loading onto the aircraft.
The load-bearing capacity of the unloading area at the destination port, the truck transfer route, and the warehouse floor must also be considered.
Heavy Cargo Checklist
[ ] Individual piece weight and base contact area have been confirmed
[ ] Drawings of support legs, bases, and center of gravity have been provided
[ ] The airline/GHA has performed a load assessment
[ ] Material, dimensions, and placement of dunnage have been confirmed
[ ] Wooden materials comply with destination country requirements
[ ] Loading and unloading equipment at the ports of origin and destination have been confirmed
[ ] Lashing, anti-slip, and securing plans have been defined
[ ] Floor load capacity of trucks and warehouses at the destination port has been confirmed
A Case Study on Heavy Cargo: Four Support Legs Turn 3 Metric Tons into a High-Risk Load
A piece of equipment weighed a total of 3 metric tons, which the customer considered “not particularly heavy.” However, the equipment had only four metal support feet, each with a very small contact area. At a glance, each foot bore approximately 750 kg, with the pressure concentrated on a very small area. If placed directly on an air waybill pallet or the aircraft floor, the localized pressure could exceed the limit.
The solution in this case is not simply to refuse the shipment, but to design shims to distribute the weight over a larger area.
Original Condition
Risks
4 Small Feet
High point load
Direct metal contact
May damage the panel surface
Center of gravity is too high
Unstable during movement
No slip resistance
Risk of shifting during flight and loading/unloading
Improvements
Value
Increase the pad area
Reduce pressure per unit area
Add anti-slip material
Reduce displacement
Emphasize the center of gravity
Facilitate lifting and securing
Confirm location with the airline
Compliance with floor load capacity
This case illustrates that with heavy air cargo, it’s not about whether the “tonnage is intimidating,” but rather where the weight is distributed.
Thicker Pallets Aren’t Necessarily Safer
Many people assume that thicker pallets are safer. In reality, pallet design must take into account strength, weight, height, stability, and operational space. If a pallet is too thick, it may cause the overall height of the cargo to exceed limits; if it is too heavy, it increases billing and loading burdens; and if the pallet material does not comply with regulations, it may also lead to quarantine issues in the destination country.
Pallet Issues
Consequences
Too Thin
Insufficient load distribution
Too Thick
Increases height, may exceed the profile
Too narrow
Point loads remain concentrated
Material non-compliant
Customs clearance/quarantine risks
Not secured
Pallets and cargo may shift relative to each other
For heavy cargo shipments, the palletization plan should be an integral part of the loading plan, rather than relying on pallets sourced ad hoc at the airport.
How Customers Can Reduce Heavy Cargo Air Freight Costs in Advance
Increase the base contact area when designing packaging;
Provide support legs and a center of gravity diagram in advance;
Ensure equipment is as forklift-accessible and crane-liftable as possible;
Avoid adding irregular supports at the last minute;
Ensure wooden materials are treated to meet compliance requirements in advance;
Confirm load-bearing capacity with both the destination port’s trucking companies and warehouses in advance.
While these steps may seem like packaging details, they actually affect the equipment type, pallet configuration, loading/unloading equipment, and costs.
Why Do Quotes for Heavy Cargo Often Require Confirmation Before Being Provided?
Customers sometimes feel that freight forwarders are slow to provide quotes. In reality, quoting for heavy cargo requires first assessing its transportability. Without information on the base, center of gravity, contact area, and dunnage plan, any quoted price is merely an estimate.
Missing Information
Quotation Risks
No bottom view diagram
Unknown whether point loads are exceeded
No center of gravity
Unknown lifting and securing risks
No contact area
Cannot determine the shim solution
No information on the destination port
Unloading and transshipment costs are unknown
No information on packaging materials
Unclear quarantine and structural integrity risks
Professional heavy cargo quotes typically follow a two-step process: first, a budget range is provided; then, a formal quote is issued after the carrier and GHA confirm the loading plan. This approach is more responsible than quoting a low price initially and then continuously adding fees later.
Heavy Cargo and Insurance
Heavy cargo typically involves high-value goods and complex equipment; should damage occur during loading or unloading, claims disputes can be difficult to resolve. We recommend that customers confirm insurance coverage in advance, particularly whether coverage extends to crane operations, loading onto and unloading from aircraft, and ground transportation.
Risk Factors
Should These Be Included in Insurance Coverage?
Loading at the Factory
Yes
Unloading at the airport
Yes
Palletizing and Dampening
Yes
Loading/unloading the aircraft
Yes
Transshipment at the destination port
Yes
Storage pending
Depends on the project
Insurance cannot replace professional handling, but it can reduce the financial risk associated with high-value shipments.
Internal Approval Process for Heavy Cargo Air Freight
It is recommended that freight forwarders establish internal approval thresholds for heavy cargo. For example, when a single piece exceeds a certain weight, the base contact area is unclear, the center of gravity is unknown, or the shipment requires crane handling or special pallets, sales representatives cannot directly confirm space allocation; instead, operations, warehousing, and the airline/GHA must be involved in the assessment.
Approval Criteria
Purpose
Single-Piece Weight
Determine whether it exceeds standard operational capabilities
Base Area
Determine point load risk
Center of Gravity and Lifting Points
Determine loading and unloading stability
Packaging Base
Assessing Palletization and Securing
Port of Destination Equipment
Determining Whether Unloading Is Possible
Insurance Requirements
Assess project financial risks
Heavy-cargo approval is not intended to reduce efficiency, but rather to prevent sales teams from applying standard cargo logic to high-risk projects.
Template for Client Documentation
You may require clients to provide the following information using a standardized template: cargo name, intended use, number of pieces, dimensions per piece, gross weight per piece, photos of the base, leg dimensions, center of gravity, lifting points, forklift pockets, whether the cargo can be tilted, whether it can be disassembled, packaging material, and unloading method at the port of destination.
If a client is unable to provide this information, it at least indicates that their internal project management is not yet mature. Freight forwarders can assist, but cannot make assumptions about the equipment’s structure on the client’s behalf.
On-Site Discipline for Heavy Cargo Operations
The biggest no-no at a heavy-lift site is having multiple people giving orders at the same time. For every step—whether it’s lifting, forklift handling, loading onto high-lift equipment, or loading into the cargo hold—there must be a clearly designated person in charge. The client’s engineer may offer advice on the equipment, but airport and airline safety requirements must take precedence.
On-Site Discipline
Reason
Unified Command
To prevent collisions between forklifts, cranes, and personnel
Move Slowly
Prevent tilting caused by shifts in the center of gravity
Verify at Every Step
Prevent misalignment of bases, pads, and tie-downs
Do not forcefully push the load
Prevent damage to cargo and aircraft structures
Heavy cargo is not loaded onto an aircraft by brute force, but through force calculations, properly matched equipment, and on-site discipline. The more urgent the customer is, the more we must slow down on-site to verify everything.
The Final Criteria
If no one can clearly explain “where the weight is concentrated” for this heavy cargo shipment, do not rush to confirm cargo space. Only when the load path can be clearly explained are you qualified to discuss loading; if it cannot be explained, you are simply passing the risk on to the airport operations team. The more urgent the heavy cargo shipment, the more important it is to clarify the load distribution first.
The professionalism of a heavy-lift project is often demonstrated at this very step: calculate everything clearly first, then discuss speed.
If the client only pressures for speed and is unwilling to provide additional documentation, the freight forwarder must stand firm on their bottom line. Because once a problem arises on-site with heavy cargo, the losses far exceed the cost of a single shipment.
The more complete the documentation, the faster the process actually becomes.
This is the fundamental principle of project logistics.
The heavier the cargo, the more patience is required.
Patience itself is a professional skill.
It is also a measure of safety.
Professional Summary
The core of air freight for heavy cargo is pressure control. Padding is not merely decorative; it is a critical tool that ensures the aircraft floor, ULD, and cargo base share the load safely.
For freight forwarders, when handling heavy cargo, it is essential to shift from a “gross weight mindset” to a “load distribution mindset.” Asking about the weight of individual items, contact area, center of gravity, and base is far more important than simply asking the price per kilogram.
This article is intended as an industry knowledge and practical reference and does not constitute advice on aviation load engineering or loading safety. For specific floor load capacities, pad calculations, and securing solutions, please refer to the recommendations of airlines, ground handlers, and professional engineers.
