Why magnets are regulated air cargo
The concern is navigation. Aircraft carry magnetic compasses and magnetometer-based sensors, and a sufficiently strong field in the hold can deflect them. The regulation is not about the magnets being dangerous in themselves — it is about the field reaching the flight deck.
The United States domestic nuance
Under the U.S. Hazardous Materials Regulations, magnetized material is treated in a binary way: under 49 CFR 173.21(d) it is either not of sufficient strength to be regulated, or it is forbidden in transportation. The graduated middle band described below comes from the ICAO Technical Instructions and IATA DGR, which is what governs international air movements and what carriers apply in practice.
The three bands
PI 953 defines the outcome by measured field or, equivalently, by compass deflection at a stated distance from the assembled package.
| Band | Condition | What is required |
|---|---|---|
| Unrestricted | Compass deflection less than 0.5° at 2.1 m (7 ft) | Nothing beyond ordinary packaging. Ships as general cargo. |
| Regulated | Above that floor, but not more than 2° deflection at 4.6 m (15 ft) — equivalent to 0.418 A/m (0.00525 gauss) at 4.6 m | Prior arrangement with the operator; magnetized material handling label; the words “magnetized material” and the package count in the Nature and Quantity of Goods box on the air waybill. A Shipper’s Declaration for Dangerous Goods is not required. PI 953 packing conditions apply. |
| Above the ceiling | More than 2° deflection at 4.6 m | Transport only with prior approval of the appropriate authority of the State of origin and the State of the operator. In commercial practice, carriers refuse it — the field has to be brought down by shielding, keepers or repacking. |
The point most shippers miss
The threshold applies to the assembled package or consignment, measured from any point on its surface. This means the same magnets can pass or fail depending entirely on how they are packed — orientation, spacing, shielding and the arrangement of cartons on a pallet. A shipment refused at the airport is very rarely a product problem. It is a packing problem, and it is fixable.
How the measurement is made
Two accepted methods. Both measure the assembled, closed package as it will be tendered — not the contents.
Instrument method
- Equipment sensitivity: the instrument must be capable of measuring fields greater than 0.0398 A/m (0.0005 gauss) within a tolerance of ±5%. Ordinary industrial gaussmeters are typically several orders of magnitude too coarse for this.
- Zero against the local field first, then introduce the package at the measurement distance.
- Rotate the package through 360° in the horizontal plane and record the maximum reading. Magnet orientation inside the carton makes the field markedly directional.
- If the maximum exceeds 0.418 A/m, apply shielding and re-measure until the reading is at or below the limit.
Compass method
- Two points 4.6 m (15 ft) apart, aligned east–west, in an area free of magnetic interference other than the earth’s field.
- Compass on one point, package on the other, rotated 360° in the horizontal plane.
- Record the maximum deflection. The compass must be sensitive enough to read a two-degree variation, preferably in one-degree increments or finer.
Where the test goes wrong
- Testing indoors near structural steel. Rebar, racking and steel decking distort the reading in both directions. The test area must be genuinely clear.
- Testing one carton and shipping ten. Fields add. A consignment must be assessed as it will be tendered.
- Not rotating the package. A single-axis reading routinely misses a maximum two to three times higher.
- Re-packing after testing. Any change to orientation, spacing or shielding invalidates the measurement.
Packing and shielding to pass
Ranked roughly by effectiveness per unit of cost and effort. Most shipments that fail need only the first three.
| Technique | How it works | Effectiveness | Cost |
|---|---|---|---|
| Opposing orientation | Arrange magnets so adjacent poles oppose, cancelling much of the external field | High — often the single biggest reduction | None, if planned into the packing method |
| Keeper bars and plates | Soft iron closes the magnetic circuit, containing flux inside the assembly. Explicitly named in PI 953 | High | Low |
| Steel shielding | Steel-lined cartons or soft iron sheeting redirect and contain the field | High | Moderate; adds weight, which matters on air freight |
| Increased standoff | Placing product centrally with void fill increases the distance from magnets to package surface | Moderate — field falls steeply with distance | Low; costs dimensional weight |
| Splitting the consignment | Fewer magnets per package reduces the field per package | Moderate | More cartons, more handling |
| Ship unmagnetized | No field, no classification, no restriction | Complete | Requires a magnetizing station at destination |
The option worth designing around
Sintered magnets can be manufactured, machined, plated and shipped unmagnetized, then magnetized in a fixture at final assembly. It removes the air cargo classification entirely, and it also removes handling injury risk, snap-together chipping in transit and the need for spacer packaging — while allowing denser packing. The trade is that the magnetizing fixture and the process step become yours. Where a product line ships magnets internationally at volume, this is frequently the right structural answer rather than a workaround, and it has to be agreed at RFQ stage. See how to prepare a magnet RFQ.
Packing that protects the product as well as the compass
- Prevent movement absolutely. Magnets that shift in transit snap together and chip — sintered material is brittle, and the damage is often invisible until the parts are used.
- Interleave with non-magnetic spacers — foam, card or plastic — sized so parts cannot reach each other.
- Retain desiccant and sealed barriers where the coating specification depends on humidity control.
- Mark the outer packaging with lot identity so receiving can tie parts to certificates without opening sealed inner packs.
- Keep pallets away from steel dunnage in the warehouse — attraction across a gap damages both.
Labelling and documentation
For shipments in the regulated band, the paperwork is lighter than most shippers expect — but the parts that are required are strictly required.
Two practical cautions
Express carriers apply their own rules. Integrator networks frequently impose stricter internal limits than the IATA minimum, and acceptance can vary by origin station. A package compliant with PI 953 may still be refused by a particular carrier’s policy. Check before booking, not at the counter.
Returns are shipments too. Rejected material going back to a supplier by air is subject to exactly the same rules, and the returning party usually has neither the packing materials nor the prior arrangement. Agree the return method before parts leave your dock — see handling nonconformance.
Mode selection
| Mode | Field restrictions | Practical notes |
|---|---|---|
| Ocean | None | The default for production volume. Packaging still needs to prevent movement and corrosion over a longer transit |
| Road and rail | None | Secure against movement; keep away from vehicle structures and electronics |
| Air freight | Full PI 953 regime | Prior arrangement essential; allow time for shielding and testing in the schedule |
| Air express | PI 953 plus carrier-specific policy | Most restrictive. Small quantities and samples; confirm acceptance before booking |
| Passenger baggage | Effectively prohibited at any meaningful size | Not a route for production parts, whatever the urgency |
Where shielding is being designed rather than improvised — and the same principles apply to containing stray field in a product as in a carton — the materials and their saturation limits are covered in magnetic shielding and flux containment.