Lost control link, a 'continue mission' failsafe and greenhouse damage
A 3.8 kg fixed-wing mapping drone is on a 40-minute pipeline inspection at 80 m AGL, 600 m from the pilot, using 2.4 GHz for control and 920 MHz for telemetry. When the aircraft turns behind a low ridge, the control link drops, although telemetry packets continue to arrive. The failsafe was left set to 'continue mission' by a previous operator. Battery is at 42%. The pilot waits 30 seconds; the aircraft continues away and the visual observer loses sight. It later crashes into a greenhouse, damaging panels; no one is injured. The operator has third-party liability insurance with a deductible and has not yet notified the insurer. The pilot wants to retrieve the aircraft quickly and continue the job with a spare.
1. Why did the 2.4 GHz control link fail while 920 MHz telemetry continued, and what was wrong with the failsafe setting?
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2.4 GHz is more strongly affected by terrain, vegetation and obstruction of the Fresnel zone than 920 MHz. Behind the ridge, the control link dropped, while the lower-frequency telemetry still received enough signal to deliver packets. That does not make the aircraft controllable: telemetry confirms the aircraft is still powered and reporting, but it does not restore command authority. The failsafe was set to 'continue mission', which is unsuitable for an inspection flight in a non-segregated area. A lost-link failsafe should have been configured for the site and approved procedure, such as hold, return or land, with a safe altitude and geofence. Continuing the mission after control loss allowed the aircraft to fly further away, lose visual contact and create an unmanaged hazard.
2. What should the pilot and observer do immediately after losing sight and after the crash?
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After losing sight, the pilot should treat the aircraft as overdue, stop the mission and attempt only safe recovery actions: check telemetry for last position and heading, call the observer, and alert the site contact. The pilot should not chase the aircraft by car or enter unsafe terrain. After the crash, the first priorities are people and property: make sure no one is injured, secure the greenhouse area, and prevent fire or further damage. The pilot should not move the aircraft before recording the scene unless it is necessary for safety. Record time, location, aircraft state, telemetry logs, weather and witness details, photograph the damage, and contact the greenhouse owner. The spare aircraft should not be flown until the cause and legal position are understood.
3. What are the reporting, insurance and liability issues?
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The operator is liable for the third-party damage to the greenhouse, and the liability insurer should be notified promptly under the policy conditions. The deductible means the operator will bear part of the loss. The insurer will also examine whether the flight was lawful and within the policy conditions, including registration, approvals, VLOS and failsafe settings. A 'continue mission' failsafe and loss of visual contact may create coverage and liability problems. The operator should assess whether the crash meets the applicable accident-reporting threshold and notify MLIT as required, and should contact police if the circumstances involve injury, significant property damage or a dispute. The pilot should preserve logs and avoid making admissions of fault before the facts are established. Continuing the job with a spare before investigation would compound the original error.