Aircraft cargo handling
Wire harnesses for aircraft cargo loading systems
Powered cargo loading systems move containers and pallets through a freighter's main deck or a passenger aircraft's lower hold. Their wiring is aircraft wiring, with everything that implies.
What is wired in a cargo loading system
A powered cargo handling system typically combines:
- Power drive units (PDUs), the motorized rollers set into the floor that move unit load devices (ULDs) along the deck;
- control panels at the cargo door and along the compartment, used by the loaders;
- sensors that report ULD position and whether locks and restraints are engaged;
- the power and data harnesses connecting them, running beneath the floor alongside structure, drains and other systems.
Patent literature on these systems describes PDUs installed in rows along both sides of the deck centerline, coordinated by a main controller unit and operated from a main control panel, with local panels along the compartment. The harness therefore carries both power to many motors and control and sensor signals back to a central controller, along the full length of the hold.
The environment is harsh even by aircraft standards: spilled liquids, debris, vibration, cold soaks, and maintenance access that means connectors are disturbed more often than elsewhere on the airframe.
The rules that apply
| Reference | What it covers |
|---|---|
| 14 CFR Part 25, Subpart H (EASA CS-25 equivalent) | Electrical wiring interconnection systems (EWIS) on transport-category aircraft, including separation, protection, identification and flammability. |
| SAE AS50881 | Wiring for aerospace vehicles: wire selection, routing, clamping, bend radius, identification and protection. |
| SAE AS22759 family | Fluoropolymer-insulated aerospace wire, widely used in airframe harnesses. |
| MIL-DTL-38999 and similar | Circular connectors common in harsh-environment aerospace harnesses. The aircraft or equipment maker's parts list governs. |
| SAE AIR4165 | An SAE Aerospace Information Report giving general requirements for powered drive units in aircraft cargo systems; SAE's catalog lists it as AIR4165A. |
| IPC/WHMA-A-620, Class 3 | Workmanship and acceptance criteria for the harness itself. |
| AS9100 / AS9102 | The aerospace quality system and first article inspection requirements usually flowed down to harness suppliers. |
Approval matters as much as workmanship
A harness that meets every workmanship criterion is still not an airworthy part on its own. Parts for type-certificated aircraft are normally produced under the type-certificate holder's production approval, through its approved supply chain, or under a separate approval such as a Parts Manufacturer Approval (PMA). Installation needs approved data. Before sourcing, establish where your harness sits in that chain and which approvals and flowdowns your supplier must work under. Ground-support equipment and test rigs are usually outside these rules, but often borrow the same workmanship standards.
Build details worth specifying
- Protection under the floor: conduit or sleeving where the harness passes fluid-exposed areas, and drip loops where connectors could collect liquid.
- Connector sealing and backshells suited to frequent disconnection during maintenance.
- Wire identification at the intervals your data requires, legible for the life of the aircraft.
- Separation between power and signal runs, and from other systems as the EWIS rules require.
- Test records per serial number: continuity, insulation resistance and dielectric withstanding voltage as specified, kept with the build traceability.
Main deck and lower deck
Freighter main decks and passenger-aircraft lower holds use the same building blocks, but the harness constraints differ. Lower deck systems work in a shallow compartment beneath the cabin floor, with limited routing space and close proximity to other systems. Main deck freighter systems cover a larger area with more PDUs and longer runs back to the controller. In both, the harness is installed around structure that cannot be modified without approved data, so routing and clamping follow the airframe maker's installation drawings.
Common questions
What is a PDU on an aircraft cargo deck?
A power drive unit is a motorized roller set into the cargo floor that rises to contact a unit load device (ULD) and drives it along the deck. A deck has many of them, controlled together.
Can a commercial wire harness shop build cargo system harnesses?
Only within the aerospace approval chain for the part. The shop must work to the design holder's drawings, the specified aerospace materials and the quality flowdowns, and the part must be produced under an appropriate production approval.
Which wire is used in these harnesses?
Whatever the approved design specifies. Fluoropolymer-insulated wire from the SAE AS22759 family is common in airframe harnesses, but a substitution needs engineering approval.
Do ground-support loaders fall under the same rules?
Ground-support equipment is not part of the aircraft type design, so aircraft EWIS rules do not apply to it directly. Operators often still specify aerospace-style workmanship because the equipment works around aircraft.
What to send a supplier
- The approved drawing and parts list, at the current revision, and the approval under which the part will be produced.
- Quality flowdowns: quality system, first article inspection, counterfeit parts prevention and record retention.
- Wire, connector, sleeving and marking specifications, with any approved alternates.
- Test requirements and acceptance criteria, and the records you need with each serial number.
- Packaging and handling requirements to protect connectors and backshells.
For the environmental side of the specification, see how to specify transport cables. For choosing a supplier who can work under aerospace flowdowns, see Best Cable Mfg's supplier guide.
Last reviewed 2026-09-17