Loading Limitations, Cargo Aircraft Only (CAO) & ULD Rules

Loading Limitations, Cargo Aircraft Only (CAO) & ULD Rules

Once a dangerous goods consignment passes acceptance verification, load planners and ramp handling agents must ensure the cargo is stowed, secured, and loaded in full compliance with aircraft operational limitations, structural load limits, and airworthiness safety standards. The physical positioning of hazardous materials within an airframe is strictly regulated by IATA DGR Section 9.3, ICAO Technical Instructions Part 7, Chapter 2, and civil aviation airworthiness certification standards (FAR/CS Part 25). Load planning balances weight and balance criteria, thermal protection, compartment fire suppression capabilities, crew accessibility, and mechanical restraint.

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1. Passenger Aircraft (PAX) vs. Cargo Aircraft Only (CAO) Limitations

To safeguard commercial air travelers, international aviation regulations establish strict net quantity limits and prohibition thresholds distinguishing Passenger Aircraft (PAX) operations from Cargo Aircraft Only (CAO) freighter operations.

Net Quantity Thresholds (DGR Table 4.2)

• Passenger Aircraft (PAX): Permitted net quantities per package are small to moderate. High-risk materials—such as Division 1.1–1.3 explosives, Division 2.1 flammable gases in large cylinders, Division 4.2 spontaneously combustible substances in Packing Group I, and toxic liquids in Packing Group I—are completely FORBIDDEN on passenger-carrying aircraft.
• Cargo Aircraft Only (CAO): Freighters are permitted to carry significantly larger quantities per package and high-hazard chemicals forbidden on passenger flights. Packages authorized exclusively for freighters must bear the mandatory Cargo Aircraft Only (CAO) handling label (DGR Figure 7.4.B), depicting a black aircraft silhouette and danger icon on a bright orange background.

Mandatory CAO Labeling & Shipper Declaration Alignment

When a consignment is prepared for CAO transport:

1. The Shipper's Declaration must explicitly have the "Cargo Aircraft Only" box selected.
2. Every package must bear a valid CAO label placed adjacent to the primary hazard label.
3. Load planners must ensure CAO packages are stowed exclusively on dedicated cargo freighter aircraft and never placed into lower deck holds of passenger flights.

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2. Accessible Stowage Options & Special Exemptions

Under IATA DGR 9.3.2, packages bearing the Cargo Aircraft Only (CAO) label must be loaded on a freighter in a position that allows a crew member or authorized person to see, handle, and when size and weight permit, separate such packages from other cargo in flight.

The Three Compliant Stowage Options

A package bearing the Cargo Aircraft Only label must be loaded in one of the following three ways:

• Option 1 — Class C compartment: Loaded in a compartment certificated as Class C, with independent smoke or fire detection giving a flight deck warning, a built-in suppression system controllable from the flight deck, and the ability to shut off ventilating airflow. Accessibility is not required here, because containment and suppression substitute for it.
• Option 2 — Equivalent unit load device: Loaded in a unit load device fitted with a fire detection and suppression system providing a capability equivalent to a Class C compartment.
• Option 3 — Accessible stowage: Loaded so that a crew member can see, handle, and — when size and weight permit — separate the package from other cargo in flight. This is the option normally used on a main-deck Class E freighter compartment, with packages positioned along the crew aisle.

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|                      ACCESSIBLE STOWAGE REQUIREMENT MATRIX                      |
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   CAO PACKAGES ON FREIGHTER AIRCRAFT
   |-- MUST BE ACCESSIBLE IN FLIGHT (See, Handle, Separate)
   |   |-- Main Deck Class E (Positioned along crew aisle)
   |   |-- Main/Lower Deck Class C (Built-in Halon 1301 suppression)
   |   `-- Main Deck Class A / B (Direct crew physical access)
   |
   `-- EXEMPTIONS FROM ACCESSIBLE STOWAGE (Can be non-accessible):
       |-- Class 9: Miscellaneous Dangerous Goods (e.g. Lithium Batteries)
       |-- Division 6.2: Infectious Substances (UN 2814, UN 2900, UN 3373)
       |-- Class 7: Radioactive Materials (Excepted & Low Specific Activity)
       |-- Class 3: Flammable Liquids in Packing Group III (No Sub-risk)
       `-- Division 5.1: Oxidizers in Packing Group III

Reading the Rule Correctly

The three options are alternatives, not a hierarchy — satisfying any one of them discharges the requirement. Two consequences follow that candidates routinely get wrong:

1. A Class C lower-deck hold is compliant for CAO cargo even though nobody can reach it in flight. Accessibility becomes mandatory only where the compartment cannot provide Class C-equivalent detection and suppression.
2. A main-deck Class E compartment relies on accessibility, because it has no built-in suppression — a fire there is fought by shutting off ventilating airflow. That is exactly why CAO packages on a Class E main deck must sit where a crew member can reach them.

The load plan should record which of the three options each CAO consignment is carried under, and the pilot-in-command verifies the stowage against the NOTOC before departure.

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3. Civil Airworthiness Cargo Compartment Classifications (FAR / CS 25.857)

Load planners must align dangerous goods stowage with the airworthiness certification of the aircraft's cargo holds. Under U.S. FAA 14 CFR 25.857 and European EASA CS-25.857, aircraft cargo compartments are classified into distinct categories based on fire detection, fire containment, extinguishing systems, and crew ventilation controls:

Airworthiness Details & Extinguishment Mechanics

• Halon 1301 Total Flooding (Class C): Class C lower deck holds use automated fire suppression bottles charged with Bromotrifluoromethane ($CBrF_3$ / Halon 1301). Upon fire detection, the flight deck triggers primary discharge, maintaining a minimum 5% Halon concentration for 60 to 180 minutes to starve chemical combustion.
• Airflow Starvation (Class E): On main deck freighters (Class E), opening a hold door inflight would introduce fresh oxygen ($O_2$) and feed a fire. Instead, flight crews execute emergency checklists that seal cabin airflow control valves, depressurizing the compartment to starve flames of oxygen while flight crew don 100% positive-pressure oxygen masks.

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4. Unit Load Device (ULD) Identification & Tagging (DGR Fig 9.3.A/B)

A Unit Load Device (ULD) is an aircraft pallet, net assembly, or rigid container used to aggregate cargo into standardized airframe lock positions. When dangerous goods are loaded into a ULD, exterior identification tagging is legally mandatory under DGR Section 9.3.1.

DGR Tagging Specifications (Figures 9.3.A & 9.3.B)

Every ULD containing dangerous goods must display an official IATA Dangerous Goods ULD Tag mounted on the exterior in an approved container tag holder at eye level on two opposite sides:

1. Standard Dangerous Goods ULD Tag (Fig 9.3.A): Features a distinctive candy-striped red border border. Used for ULDs containing dangerous goods authorized on passenger and cargo aircraft.
2. Cargo Aircraft Only ULD Tag (Fig 9.3.B): Features a solid bright orange border. Used whenever the ULD contains one or more packages bearing the Cargo Aircraft Only (CAO) label.

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|                   IATA DANGEROUS GOODS ULD TAG DATA FIELDS                      |
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|  [ RED CANDY-STRIPED BORDER (PAX)  /  SOLID ORANGE BORDER (CAO ONLY) ]          |
|                                                                                 |
|  ULD IDENTIFICATION NUMBER:  AKE 45892 DL                                       |
|  AIRPORT OF DISPATCH:        ATL                                                |
|  AIRPORT OF DESTINATION:     FRA                                                |
|                                                                                 |
|  HAZARD CLASS / DIVISION:    Class 3 (Flammable Liquids), Div 6.1 (Toxic)       |
|  UN NUMBERS ENCLOSED:        UN 1090, UN 2810                                   |
|  TOTAL NET QUANTITY:         150 L / 45 kg                                      |
|  ACCESSIBLE / INACCESSIBLE:  ACCESSIBLE                                         |
|                                                                                 |
|  SIGNATURE OF LOAD PREPARER: [ J. Doe ]             DATE: 2026-08-11            |
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Primary ULD Container Types in Airline Operations

• AKH Container: Half-width lower deck container designed specifically for narrowbody aircraft (e.g., Airbus A320 family).
• LD3 / AKE Container: Standard full-width lower deck container used across widebody aircraft (e.g., Boeing 777, 787, Airbus A350).
• PAG / PMC Pallets: Flat aluminum aircraft pallets secured with heavy-duty structural cargo nets and tie-down straps.
• Fire Containment Covers (FCC): Specialized fire-resistant Kevlar/Nomex fabric covers placed over palletized cargo (frequently used when transporting UN 3480 Lithium Ion Batteries) capable of containing a 1,000°C thermal runaway fire for over 4 hours.

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5. Aircraft Restraint, Floor Loading & Dynamic G-Force Limits (FAR / CS 25.561)

Dangerous goods packages must be physically restrained within the airframe to prevent movement during normal flight turbulence, extreme maneuvers, and emergency landing scenarios. A shifting dangerous goods package can alter the aircraft's Center of Gravity (CG) or rupture, releasing toxic or flammable liquids into structural bilges.

Emergency Landing Dynamic Load Factors (FAR/CS 25.561)

Under civil aviation airworthiness codes (14 CFR 25.561 and CS 25.561), all cargo hold structures, ULD locks, floor tie-down rings, and restraint straps must withstand Ultimate Dynamic G-Force Design Loads without structural failure:

$\text{Design Load (kgf)} = \text{Cargo Mass (kg)} \times \text{G-Factor}$

Floor Load Intensity Limits & Wet Cargo Separation

• Floor Load Intensity Limit (kg/m²): Load planners must verify that package mass divided by floor contact area does not exceed structural deck limits (e.g., 500 kg/m² for lower holds). Heavy chemical drums must be placed on load-spreading dunnage pallets.
• Separation from Wet Cargo: Dangerous goods packages constructed of corrugated fiberboard (4G) must be stowed away from wet cargo (e.g., fresh seafood on wet ice, live animals) to prevent moisture absorption and structural degradation of outer boxes.
• Orientation Maintenance: Liquids must be loaded strictly with "THIS SIDE UP" orientation arrows pointing skyward to ensure pressure relief valves and container closures remain above liquid levels.

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6. Practical Loading Exam Case Study

Scenario Audit

A Boeing 777-200F freighter is being loaded at Chicago O'Hare (ORD) for a flight to Frankfurt (FRA). The load plan includes three specific dangerous goods consignments:

1. Item A: 4 steel drums of UN 1263, Paint, Class 3, PG II, net weight 100 L per drum, labeled CAO.
2. Item B: 2 boxes of UN 3480, Lithium ion batteries, Class 9, declared CAO.
3. Item C: 1 package of UN 2014, Hydrogen peroxide, aqueous solution, Div 5.1 (Sub-risk Class 8), PG II, net weight 20 L, labeled PAX.

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|                      CASE STUDY LOADING AUDIT EVALUATION                        |
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| ITEM A: UN 1263 Paint (Class 3 PG II, CAO)                                      |
|   - ACCESSIBILITY: Use Option 1 (Class C hold) or Option 3 (accessible stowage).|
|   - STOWAGE: Must be positioned along main deck aisle. Cannot be stowed in      |
|     an enclosed non-accessible lower hold unless Class C equipped with Halon.   |
|                                                                                 |
| ITEM B: UN 3480 Lithium Batteries (Class 9, CAO)                                |
|   - ACCESSIBILITY: Satisfied by Option 1 if loaded in a Class C hold.            |
|   - STOWAGE: May be loaded in a non-accessible Class C lower deck hold, or on    |
|     the main deck under Option 3. Fire Containment Cover recommended.           |
|                                                                                 |
| ITEM C: UN 2014 Hydrogen Peroxide (Div 5.1, Sub-risk 8, PG II, PAX)             |
|   - ACCESSIBILITY: Permitted on PAX aircraft; accessible loading not required.  |
|   - SEGREGATION AUDIT vs ITEM A: Must check Table 9.3.A between Div 5.1/Sub 8  |
|     and Class 3. Table 9.3.A requires 'X' segregation! Cannot be loaded in    |
|     same ULD or adjacent to Item A (UN 1263). Must maintain 1.0m separation.   |
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