Drone 4kg Weight Threshold in the UK

4kg: The A2 Ceiling

The 4kg threshold marks the upper boundary of the C2/UK2 class. This class is the gateway to the Open A2 subcategory, which allows pilots holding an A2 Certificate of Competency to fly within 30 metres of uninvolved people at normal speed, or within 5 metres in low-speed mode (maximum 3 m/s). No heavier drone can access A2.

For operators choosing a drone for professional or semi-professional work in populated areas, 4kg represents the practical ceiling of what you can fly near people under the Open Category. Drones at or near this weight include advanced cinematography platforms, survey-grade mapping drones, and larger multi-rotor systems with high-specification cameras and sensors.

The distinction is absolute: a 3.9kg class-marked C2 drone with an A2 CofC pilot can fly within 30 metres of people in a town centre. A 4.1kg drone, regardless of class mark or pilot qualifications, cannot. It is relegated to A3 and the 150-metre distance rule.

Above 4kg: C3/UK3 and C4/UK4 Classes

Drones weighing more than 4kg but no more than 25kg fall into the C3/UK3 or C4/UK4 classes. The distinction between C3 and C4 lies in the drone's construction and intended use:

• C3/UK3: Factory-built drones with a maximum characteristic dimension (largest span including propellers) of no more than 3 metres. Must have direct remote identification, geo-awareness, and defined maximum operational altitude. Maximum MTOM is 25kg.
• C4/UK4: Designed primarily for privately built or modified drones. Must not have any automatic flight mode except for emergency stabilisation and return-to-home assistance. Maximum MTOM is 25kg. No requirement for remote identification or geo-awareness, reflecting the hobbyist and experimental nature of aircraft in this class.

Both C3 and C4 drones are restricted to the Open A3 subcategory. The 150-metre distance from built-up areas applies to all operations. There is no path from C3 or C4 into A1 or A2, regardless of pilot qualifications or operational experience.

Legacy Drones Above 4kg

Legacy drones (those without any class mark) weighing above 4kg operate under the same A3 restrictions. The transitional provisions treat all legacy drones between 250g and 25kg identically: A3 only, 150 metres from built-up areas. Whether a legacy drone weighs 500g or 15kg, the geographical restriction is the same.

However, heavier legacy drones face additional practical scrutiny. A 10kg drone falling from 120 metres carries substantially more kinetic energy than a 2kg drone at the same altitude. Operators of heavier aircraft should apply proportionally greater caution in their pre-flight risk assessments, site selection, and emergency planning.

The 25kg Open Category Maximum

The Open Category has an absolute weight ceiling of 25kg MTOM. Any drone above this weight cannot operate under Open Category rules, regardless of class mark, pilot qualifications, or operating environment. Operations with drones exceeding 25kg require either:

• Specific Category: An Operational Authorisation (OA) from the CAA based on a risk assessment, typically using the SORA methodology. The OA defines the specific conditions under which the drone may operate.
• Certified Category: For the highest-risk operations, including operations over dense assemblies of people, transport of people, or transport of hazardous cargo. The drone must hold a type certificate, the operator must hold an operating licence, and the pilot must hold a remote pilot licence.

Most consumer and prosumer drones fall well under the 25kg limit. The threshold primarily affects industrial drones used for heavy-lift operations, agricultural spraying, construction surveys with specialised equipment, and emergency service applications.

Weight Classes at a Glance

The following table summarises the UK drone weight classes and their corresponding subcategory access within the Open Category:

• C0/UK0 (under 250g): Open A1. Can fly over uninvolved people if class-marked. Legacy under 250g: A1 but no overflight of uninvolved people.
• C1/UK1 (under 900g, below 80J kinetic energy): Open A1. Can fly near uninvolved people. Requires Flyer ID.
• C2/UK2 (under 4kg): Open A2. 30m from people (5m in low-speed mode). Requires A2 CofC.
• C3/UK3 (under 25kg, max 3m dimension): Open A3 only. 150m from built-up areas.
• C4/UK4 (under 25kg, no auto modes): Open A3 only. 150m from built-up areas.
• Legacy (250g to 25kg, no class mark): Open A3 only. 150m from built-up areas.
• Above 25kg: Not permitted in Open Category. Requires Specific or Certified Category authorisation.

Why 4kg Matters for Purchasing Decisions

If you are purchasing a drone for work that involves flying in or near populated areas, the 4kg boundary should heavily influence your choice. A drone under 4kg with a C2/UK2 class mark, combined with an A2 CofC qualification, gives you the broadest practical operating envelope within the Open Category for operations near people.

Once you exceed 4kg, your drone is permanently restricted to A3 operations in the Open Category. The only way to fly a heavier drone near people or in built-up areas is to obtain an Operational Authorisation under the Specific Category, which involves a detailed risk assessment, potentially longer processing times, and ongoing reporting requirements.

The practical difference is significant. An A2-qualified pilot with a C2 drone under 4kg can arrive at a site in a suburban area and begin operations after a standard pre-flight check. The same pilot with a 5kg drone in the same location would need an OA, which typically takes weeks or months to obtain from the CAA.

Insurance and Liability Considerations

Heavier drones carry greater liability exposure. The potential for property damage and personal injury increases with mass, and insurers price their policies accordingly. Third-party liability insurance is mandatory for commercial operations regardless of drone weight, but the premium for a 4kg or heavier drone will typically exceed that for a sub-250g aircraft.

For recreational operators, insurance remains optional but increasingly advisable as drone weight increases. A 4kg drone striking a vehicle windscreen, a building facade, or a person presents a materially different risk profile from a 250g drone in the same scenario. The financial exposure from a single uninsured incident could far exceed the cost of years of insurance premiums.

Specific Category Operations for Heavier Drones

For operators who need to fly drones above 4kg in populated areas, the Specific Category provides a structured path. The process involves:

1. Risk assessment: Conducting a SORA (Specific Operations Risk Assessment) that evaluates ground risk, air risk, and the mitigation measures in place.
2. Application: Submitting the risk assessment and an operations manual to the CAA as part of an Operational Authorisation application.
3. Review: The CAA reviews the application and may request additional information, modifications to procedures, or additional mitigations.
4. Authorisation: If approved, the OA specifies the conditions under which operations may be conducted, including geographical limitations, altitude restrictions, crew requirements, and reporting obligations.

The timeline varies depending on the complexity of the operation and the CAA's workload. Operators should allow several weeks for routine applications and potentially longer for novel or complex operations.

Summary

• 4kg is the C2/UK2 class ceiling and the maximum weight for Open A2 subcategory operations.
• Above 4kg: C3/UK3 or C4/UK4 class, restricted to Open A3 (150m from built-up areas).
• 25kg is the Open Category maximum. Above 25kg requires Specific or Certified Category authorisation from the CAA.
• Purchasing impact: A drone under 4kg with a C2 class mark provides the broadest Open Category permissions for flying near people.
• Heavier drones near people: Require an Operational Authorisation under the Specific Category, involving SORA risk assessment and CAA approval.
• All standard Open Category rules apply to drones at or below 25kg: 120m altitude, visual line of sight, restricted airspace, registration requirements.