Tethered Drones: When They Beat Battery Flight

DJI rates the Matrice 4T and 4E at up to 42 minutes of hover, measured with standard props in no wind from 100% to 0%. Real jobs land well before that. For most work that's plenty. For a few jobs it isn't, and that's where a tether comes in.

A tethered drone (a drone powered through a cable from a ground unit instead of only by its flight battery) trades range for time in the air. Here's where that pays off, where it doesn't, what exists for the Matrice 4 series, and which FAA rules still apply.

How a tethered setup works

A typical system has a ground station with a powered reel, a thin cable that carries power up, and an air module on the aircraft. The ground station needs its own power, usually a generator or shore power. Most systems keep the flight battery in as a backup so the drone can land if ground power drops. The result is a drone that can sit over one spot as long as the power lasts, but only within the reach of the cable.

Where a tether beats battery flight

Persistent overwatch

This is the main reason agencies and security teams buy tethers. A crash scene, a standoff, a large fire or a search staging area can run for hours. A tether gives the incident commander a steady overhead view without landing every half hour to swap batteries. On a 4T that view includes thermal, which matters at night. Our post on how police departments use thermal drones covers the day-to-day side.

Events

Fairs, parades, rodeos and concerts are long, and security needs a view of the same few spots all day: entrances, parking and exit routes. A tethered drone parked at the edge of the crowd does that well. The tether doesn't change the rules about flying over that crowd (more below).

Disaster response, comms and lighting

After a storm or wildfire, a drone that stays up can hold a light over a work area or carry a radio relay. Be realistic about payload. DJI lists a maximum payload of 200 g for the Matrice 4 series. That's enough for DJI's own AL1 spotlight (99 g with clamp) or AS1 speaker (92.5 g with clamp), but most radio relay and cellular payloads are built for larger airframes. If comms relay is the main job, the Matrice 4 is probably not the right aircraft.

Where battery flight is still the better call

A tether is a poor fit for anything that moves:

• Search grids and mapping. Tether kits advertised for the Matrice 4 list cable lengths of about 33 m or 55 m (roughly 110 to 180 ft). You can't fly a search pattern or map a field on a leash.
• Inspections. Roofs and towers need the drone to move around the structure, and a cable near one is a snag risk.
• Fast launches. A tether means setting up a ground station, starting power and managing cable before you fly.
• Wind and obstacles. The cable adds drag and has to stay clear of trees, power lines, vehicles and people.

For a lot of crews the practical answer is more batteries, not a tether. With three or four Matrice 4 batteries and a way to charge in the field, like a portable charging station, you can keep a 4T working through a long shift with short landings to swap, and you keep full mobility.

Matrice 4T and 4E: what's official and what isn't

To be straight: DJI does not list a tether in the Matrice 4 series specs or compatible accessories, and the Matrice 4 series user manual doesn't cover tethered flight. DJI's developer documentation does describe a tethered battery mode, but for the Matrice 400, not the Matrice 4.

Third-party makers do sell tether kits advertised for the Matrice 4T and Matrice 4E. They're third-party products, not DJI accessories. Before buying one, ask the maker:

• How the aircraft lands if ground power or the cable fails, and whether the flight battery stays in as a backup
• Whether DJI firmware updates have ever broken compatibility, and how fast they fix it
• Whether you can still run the spotlight or speaker with the tether module installed
• What ground power it needs. One Matrice 4 kit lists a 190–240 VAC input, so a standard 120 V outlet won't run it
• What it means for your DJI warranty or care plan

FAA rules for tethered drones

Part 107 still applies

A tether doesn't turn a drone into a kite or moored balloon. In the Part 107 final rule, the FAA said a powered small drone is not a balloon or kite under Part 101, and that small UAS includes tethered powered small UAS. For commercial work you're under Part 107, all of it:

• A remote pilot certificate (the FAA license for commercial drone pilots) for the remote PIC (the person legally responsible for the flight) under 107.12
• Visual line of sight (being able to see the drone with your own eyes) under 107.31
• The 400 ft altitude limit under 107.51, unless you're within 400 ft of a structure
• Airspace authorization in Class B, C, D or surface Class E airspace (controlled airspace around airports) under 107.41
• The operation over people rules under 107.39 and the night rules under 107.29
• Remote ID (the drone's broadcast of its ID and location) under Part 89

Neither Part 107 nor Part 89 has a tether exception. Our Remote ID guide covers that rule in more detail.

The cable counts toward weight

The FAA said in the same rule that an attached cable counts toward the 55 lb small UAS limit. If the cable is anchored to an immovable object so the drone can't fly away, only the part the drone could lift counts. That won't matter on a Matrice 4, but it can on heavy-lift setups.

Event airspace

Check the airspace first. A standing FAA flight restriction bans drones within 3 nautical miles and up to 3,000 ft above ground level of stadiums seating 30,000 or more during MLB, NFL and NCAA Division I football games and major motor speedway races, from one hour before to one hour after the event. Flights for the venue's own operations or the broadcast rights holder need an approved waiver. Other events can get their own restrictions by NOTAM (a notice to airmen), so check before every flight.

Public safety has an extra option

The 2024 FAA Reauthorization Act added a path for public safety organizations (law enforcement, fire, EMS and similar agencies) to fly actively tethered drones without a COA (certificate of authorization), a waiver, or a remote pilot certificate. Under 49 U.S.C. 44806(c), the operation has to stay at or below 150 ft above ground level (and below the UAS Facility Map ceiling where one applies), stay within visual line of sight, avoid flying directly over non-participating people, and give way to other aircraft. Going above 150 ft needs prior FAA authorization.

The system also has to meet the law's definition of "actively tethered": a taut, load-rated tether that provides continuous power and is used to control and retrieve the drone, safe flight control after a power or flight control failure, and a programmed controlled landing if the tether separates. The FAA's checklist says the drone still has to be registered and broadcast Remote ID. Part 107 has no 150 ft cap for tethered flights, so many agencies will keep flying under Part 107 or their COA.

A quick decision check

A tether is worth a look if most of these are true:

1. You regularly need eyes on one spot for longer than a couple of batteries.
2. You can set the ground station close to that spot and keep the drone in sight.
3. You have reliable ground power that meets the kit's input specs.
4. You can keep the cable clear of people, vehicles and obstacles.
5. Your airspace and the rules over people work for the site.

If not, more batteries and a field charger will usually serve you better.

Talk it through

If you're weighing a Matrice 4T, a 4E or a different setup for long-duration work, we're happy to talk it through. Call 1-877-992-8279 (M–F 9–5 MT), email sales@avarydrone.com, or request a quote.

This article is general information, not legal advice. Always check current FAA rules and guidance, and confirm third-party equipment compatibility with its manufacturer.

Sources

• 14 CFR Part 107, Small Unmanned Aircraft Systems (sections 107.12, 107.29, 107.31, 107.39, 107.41, 107.51)
• 14 CFR Part 101, Moored Balloons, Kites, Amateur Rockets, and Unmanned Free Balloons
• 14 CFR Part 89, Remote Identification of Unmanned Aircraft
• Federal Register, Operation and Certification of Small Unmanned Aircraft Systems (Part 107 final rule, 81 FR 42064, June 28, 2016): tethered small UAS and tether weight
• 49 U.S.C. 44806, Public safety use of tethered unmanned aircraft systems
• 49 U.S.C. 44801(1), Definition of actively tethered unmanned aircraft system
• FAA, Checklist for Tethered Public Safety 49 USC 44806 Operations (August 2024)
• FAA, Stadiums and Sporting Events
• FAA, Sporting Event TFR FDC NOTAM 4/3621 handout
• DJI Enterprise, Matrice 4 Series specs
• DJI, Matrice 4 Series User Manual
• DJI Payload SDK documentation, Tethered Battery (Matrice 400)
• CICI Tech, Tethered for DJI Matrice 4 (third-party product specs)