Tethered drone operations

How UK rules treat tethered drones

The CAA describes a tethered drone as one that is securely attached by a physical link at all times while flying, whether to a person, the ground or another suitable object. Powered tethered aircraft with a mass over 1 kg are subject to the same rules as any other drone, under UK Regulation (EU) 2019/947 and its Open and Specific categories.

Tethered aircraft of 1 kg or less are outside UK Regulation (EU) 2019/947. Article 265E of the Air Navigation Order 2016 covers them instead, as tethered small unmanned aircraft. It applies selected requirements, including operator registration, occurrence reporting, geographical zones, overflight of people and, for aircraft of 250 g or more, remote pilot competency. Without CAA permission, it also bans dropping material, carrying dangerous goods and flying on a restraining device longer than 25 m.

When an operation needs an operational authorization in the Specific category, the CAA notes that proposing a tethered aircraft can count as a risk mitigation. New applications go through UK SORA, where a tether can be claimed against the containment requirements. The CAA's UK SORA guidance (ORS9 Decision No. 46) sets tether-specific criteria, known as COT, as an alternative to the general containment criteria. You need to show that:

• the line is long enough to keep the aircraft inside the operational volume
• the line and its attachment points can take the ultimate loads, which the guidance defines as the maximum loads in normal and failure cases multiplied by a safety factor of 1.5
• a rotating propeller cannot cut the tether
• you have procedures to install the tether and inspect its condition periodically

EASA and EU rules for tethered drones

Regulation (EU) 2019/947 applies to tethered drones unless one of two exclusions in Annex I to Regulation (EU) 2018/1139 applies. The first is an aircraft of 1 kg or less. The second is an aircraft with no propulsion system on a tether of no more than 50 m, with a mass under 25 kg (or, for a lighter-than-air aircraft, a design volume under 40 cubic meters). In those cases national rules apply.

Standard scenario STS-01 treats tethered flights differently. Instead of the flight geography, contingency area and ground risk buffer used for free flight, the controlled ground area is a circle with a radius of the tether length plus 5 m, centred on the point where the tether is fixed. The STS-01 ground speed limit of 5 m/s applies only to untethered aircraft.

Class C2 and C3 drones flown on a tether must have a tether shorter than 50 m in tensile length. For heavier-than-air aircraft, its strength must be at least 10 times the aircraft's weight at maximum mass. Some class requirements, such as direct remote identification on a C3, apply only when the aircraft is not tethered.

For a SORA 2.5 application to a national aviation authority, EASA's acceptable means of compliance offers the same tether criteria as an alternative to the general containment requirements. The level claimed depends on assurance. At low, the designer or operator declares compliance. At medium, they need supporting evidence such as tether material specifications and test results. At high, the competent authority or an entity it designates validates the claim.

FAA rules: Part 107 and the public safety route

In the Part 107 final rule (June 2016), the FAA stated that the definition of a small UAS includes tethered powered small UAS. A powered tethered drone is not a kite or moored balloon under Part 101, so the normal Part 107 rules on remote pilot certification, operating limits, airspace and waivers apply.

The tether counts towards the 55-pound limit. The FAA said the weight of the whole cable must be added to the aircraft's weight, because the aircraft could lift all of it if control is lost. If the cable is secured to an immovable object so the aircraft cannot fly away, only the part that could be lifted aloft counts.

Public safety organizations have a separate statutory route for actively tethered systems under 49 USC 44806 (section 926 of the FAA Reauthorization Act of 2024). The FAA's checklist describes an aircraft of 55 pounds or less, excluding the tether, on a taut, load-rated tether that provides continuous power, programmed to land in a controlled way if the tether separates. Flights must stay in visual line of sight, give way to other aircraft and not pass directly over people who are not involved. They are limited to 150 feet above ground level and the UAS Facility Map ceiling unless the FAA authorizes more. Registration and Remote ID still apply.

The same checklist notes that tethered operations under Part 107 are not held to that 150-foot cap. Under Part 107, controlled airspace still needs an airspace authorization, through an FAA-approved LAANC app or FAADroneZone.

Planning points: tether strength, ground risk, airspace and weather

A tether keeps the aircraft within a known circle, but it does not stop the aircraft falling inside that circle. The line itself, and the area near the ground station, also need to be kept clear of people who are not involved. A tether limits how far the aircraft can go. It does not remove the need for permission in controlled airspace or a flight restriction zone. Wind loads the line as well as the aircraft, so set wind limits for the combined aircraft and tether from the manufacturer's data.

Treat the tether, its attachment points and the ground station as part of the system you are assessing. Record the cable's rated strength, the loads you expect, the inspection interval and the replacement criteria in the operations manual. Plan for these failure cases:

• the tether parting, which on a powered tether also cuts the power supply
• the ground station or winch failing or losing power
• the line snagging on structures, vehicles or people below
• strong wind pulling the line tight and loading the attachment points

What a consultant does, and what to ask before hiring

A consultant can confirm which regime applies, write the tether sections of the operations manual, assemble containment evidence for a UK SORA or EASA application, and answer regulator questions. They cannot grant an approval or promise an outcome: the CAA, the national aviation authority or the FAA decides. Consultants listed on DOC are vetted (identity, legal entity, sanctions screening and professional indemnity insurance), and regulator experience is shown as verified only where it has been evidenced.

• Have you claimed a tether as containment in a UK SORA or EASA SORA application, and at what level?
• How will you evidence tether strength and the ultimate loads: by test, simulation or operating records?
• What procedures will you write for installing, inspecting and replacing the tether?
• How does the plan handle a parted tether or a ground station failure?

Common mistakes

Watch for these errors when planning tethered work:

• Assuming a tether takes the aircraft outside drone rules (in the UK only aircraft of 1 kg or less leave UK Regulation (EU) 2019/947, and the Air Navigation Order still covers them)
• Leaving the cable out of the weight calculation for the FAA's 55-pound limit
• Claiming tether containment without evidence of line and attachment strength
• Ignoring hazards created by the tether itself, such as snagging or people near the ground station
• Assuming the 150-foot public safety route under 49 USC 44806 is open to commercial operators