Definition
BVLOS (Beyond Visual Line of Sight flight) refers to drones flying outside the operator's line of sight, relying on communication links, navigation systems, obstacle avoidance systems, regulatory platforms, and other means to achieve remote control, monitoring, and compliance management. BVLOS is a core capability in scenarios such as drone logistics, long-distance inspection, power line patrols, and agricultural protection. Compared to VLOS (Visual Line of Sight), it can greatly improve operational efficiency and coverage.
BVLOS has high requirements for communication links: it needs wide coverage (especially low-altitude and remote areas), low latency (remote control response < 100ms), and high reliability (anti-interference, redundant backup). 4G/5G IoT SIM cards provide cellular communication links for BVLOS, which can serve as the primary link or form redundancy with video/data transmission radios, supporting beyond visual line of sight flights. Certain scenarios require airspace and flight route approval.
Technical Features
BVLOS drones are usually equipped with multi-link communication, RTK high-precision positioning, ADS-B transponders, and electronic fences. They interface with drone cloud platforms (UOM) to achieve flight plan submission, real-time monitoring, and airspace coordination. IoT SIM cards provide stable connectivity for communication between drones, cloud platforms, and ground stations.
Use Cases
BVLOS Applied to drone logistics delivery, power/oil and gas pipeline inspection, surveying and mapping, agricultural plant protection, emergency command, forest fire prevention, marine monitoring, etc. Typical scenarios include: drone delivery, long-distance inspections, drone cloud platforms, formation flight, etc. SimtoLink provides IoT SIM cards, dedicated APN, data plans, and drone solutions for BVLOS flights.
Return and link recovery after the path breaks
In beyond-visual-line-of-sight flight, the IoT SIM is the cellular path between the aircraft and the ground station or cloud, carrying telemetry, track, remote commands, and a small amount of imagery. It does not replace inertial navigation in the flight controller, and it does not by itself make the flight a lawful beyond-visual operation. The link has three layers: whether position can still be reported, whether a critical command can still be sent, and which pre-written logic the aircraft follows after the link breaks. Those three layers must not share one failure rule. Choppy video does not mean the control link is lost. A lost control link does not mean the aircraft is out of control; the flight controller may already be returning or hovering. Writing “video is not smooth” down as a lost link triggers an unnecessary return. Writing “there is still a heartbeat” down as everything normal ignores that a command can no longer be confirmed.
The conditions include real cellular coverage along the route, an antenna installation that does not block satellite positioning, and roaming and an access point that let the aircraft move across the networks the route crosses. With two links, set the switch order in advance: which of the data or video radio and cellular is preferred, how long the switch takes, and whether non-critical uplink pauses during the switch. Lost-link timing must be written into the mission before takeoff: how long to hover, the return altitude, the alternate landing point, and whether a restored link may continue the mission or only allows a return. On volume, telemetry and track stay small and frequent. Imagery and log upload must not occupy the command path. Bind the SIM to the airframe and the flight-controller serial number, so a spare aircraft with a swapped SIM does not keep reporting into the old mission. If the route leaves the subscribed area, find that in mission planning, not as a reject cause at the edge of the flight.
A common error is to test speed only at the takeoff and landing point. Coverage there can be good while the middle of a line patrol, a valley, or the back side of a tall tower has no usable cell. The aircraft returns on the lost-link logic and the ground crew treats it as a flight-controller fault. Another error is one failure counter shared by cellular and the video link, so three dropped video frames cut the control link. Putting high-definition video, logs, and remote parameter changes at the same priority lets command confirmation pass its time limit. If the SIM may reach any public address, a ground-station address change leaves the aircraft on the old server: online, and not flying the mission. Acceptance should sample coverage along the planned route and trigger a lost link in the air or in simulation, then check that the aircraft action, the platform alarm, and the restored track are continuous. The airframe boundary is described under UAV. The cellular capability itself is still bounded by the air-interface release; see 3GPP.
Each mission should keep a link plan: which segments expect cellular, which rely only on the backup radio, and which alternate point the aircraft flies to after a lost link. Switches that actually happen in flight should be comparable with that plan, not only a smooth track after the fact. Do not fold a video-stall count into the control-failure count. A control command needs an acknowledgement. Without one, treat it as not executed. Do not assume it took effect because the aircraft is still reporting position. Upload logs after landing, so they do not compete with registration at takeoff. A spare SIM must pass the same area and access-point checks as the primary. Left unused, it is found unpaid or locked only when the switch is real. After return and landing, compare the local flight-controller log with the platform track for gaps. Treat a gap as a lost link. Do not interpolate the route so it looks continuously online. When the mission crew changes shift, hand over the unfinished catch-up queue as well, or the next shift will think the previous shift did not fly.
After landing, confirm track gaps before allowing the next sortie to reuse the same SIM and the same mission id. A repeated mission id stacks the lost-link records of two flights. List commands that lacked an acknowledgement in the review, and do not delete them because the aircraft landed safely. After an antenna change or an airframe repair, fly a coverage sample again. Do not keep the pre-repair link plan.