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Air accident investigation: Finnish Learjet 35A missed drone by 60 meters

Christian Fernsby |
A Finnish Air Force Learjet 35 A/S and Pirkanmaa Rescue Department’s remotely piloted aircraft DJI Phantom 4 Pro Obsidian were in danger of collision in Valkeakoski on 6 February 2019.

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The Air Force Learjet had set off on a refresher training flight that included low-altitude flying. A flight plan had been prepared for the flight and the route being used, and the air traffic control was aware of the plan.

When the Learjet was already in the air, the Pirkanmaa Rescue Department made an advance notification of RPAS operations in accordance with the Rescue Department’s instructions to the Tampere-Pirkkala air traffic control and started flight operations.

The information on the RPAS operations was not relayed to the air traffic controller in charge, and no flight information service was provided of the RPAS operations. The Pirkanmaa Rescue Department and ANS Finland did not have a co-operation agreement on RPAS operations, and no procedure for advance notifications had been agreed.

If the air traffic control had warned the crew of the Learjet of the collision hazard, it could have affected the selection of altitude or route so that the incident could have been avoided. Air traffic was not busy, and handling it did not prevent the provision of flight information service.

During the incident, the Learjet was flying around 10 metres lower than the remotely piloted aircraft, and their lateral distance was around 60 metres.

At that time, the remotely piloted aircraft was flying at a height of around 77 metres AGL, while the Learjet was flying at a height of around 69 metres AGL. The incident occurred quickly, and the remote controller had no time to do anything to avoid it.

The investigation identified several deficiencies in regulations and procedures related to RPAS operations.

In Finland, air traffic control lacks unified procedures for handling advance notifications of unmanned aviation and providing flight information service on unmanned aviation.

The Aviation Act and the aviation regulation OPS M1-32 on unmanned aviation are in conflict. According to the Aviation Act, an unmanned aircraft may deviate from flight rules in an area restricted from other aviation.

However, the aviation regulation enables deviation from the flight rules, so the obligation to follow flight rules in RPAS operations is unclear.

Procedures that would allow the different State aviation actors to be informed of planned, started or ending flight operations have not been investigated or adopted. This is problematic in situations involving multiple authorities, where the manned and unmanned aircraft of different authorities may be operating in the same area.

The flight preparation and geographic information applications for RPAS operations are partially undeveloped. The information in the Finnish Transport and Communications Agency’s Droneinfo application is incomplete.

For example, the application does not allow submitting a flight notification in advance. During the investigation, the Droneinfo application also did not provide information on the dynamic airspace.

RPAS operations and related incident have increased strongly over the last years. The problem has been identified in organisations carrying out low-altitude flight operations, but hardly no practical measures have been taken.

With the current regulations and technical systems, RPAS operations cause a too high risk to low-altitude flight operations. Because training in RPAS operations is voluntary, the competencies of the remote controllers vary a lot. In this case, the incident occurred although the remote controller acted in accordance with the regulations and instructions.

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