On 27 June 2019 the Supreme Court dismissed an appeal against the conviction of an air traffic controller for negligent disruption of public transport.(1) In so doing, the court established a new precedent that allows for criminal prosecution and conviction for operational incidents that result in neither injury nor damage.


The case concerned the loss of required separation between a Boeing B737, operated by Ryanair, and an Airbus A319, operated by Air Portugal, while under the control of Swiss air navigation services organisation Skyguide on April 12 2013.

At 4:10:43pm UTC the crew of the Ryanair B737 requested a climb from flight level 360 to flight level 380 due to expected turbulence, but the crew did not add the call sign RYR 3595 to their request. The Skyguide controller replied with the clearance to another Ryanair B737 bearing the call sign RYR 6DW to climb to flight level 380. The crew of the first Ryanair B737 responded with their own call sign RYR 3595 to the clearance of RYR 6DW and began to climb. Neither the controller nor the crew of RYR 6DW responded.

RYR 3595 came close to the Air Portugal A319 with call sign TAP 706, which was cruising on a crossing track on flight level 370.

At 4:11:37pm UTC the ground-based short-term conflict alert warned the controller of an impending conflict between TAP 706 and RYR 3595. At 4:11:43pm UTC the controller asked whether RYR 3595 was maintaining flight level 360 to which the crew answered in the negative. At 4:11:49pm UTC the controller instructed RYR 3595 to descend immediately which RYR 3595 acknowledged.

At the same time, the on-board traffic alert and collision system (TCAS) commanded RYR 3595 to descend and TAP 706 to climb. Both crews immediately followed their TCAS resolution advisories (RAs) and resolved the conflict.

The closest distance between the two aircraft had been 0.8 nautical miles horizontally and 650 feet vertically (the required separation minima had been either 5 nautical miles horizontally or 1,000 feet vertically).

The Swiss Accident Investigation Board (SAIB) investigated the incident and published their findings in a report on 9 October 2014.(2) The SAIB was of the view that the two aircraft had been sufficiently close to each other so that a serious risk of collision existed, as per Category A of the International Civil Aviation Organisation's (ICAO's) risk classification scheme.(3)

On that basis, the federal prosecutor brought charges against the air traffic controller.

On 30 May 2018 the Federal Criminal Court held that the controller had endangered the life of the passengers and crew of TAP 706 and RYR 3595. The court found the controller guilty under Article 237 of the Criminal Code.(4)

Article 237 penalises with a custodial sentence or a monetary penalty anyone who wilfully or negligently endangers public transport – including air transport – and thereby "causes danger to the life and limb of other people".

The court sentenced the controller to a monetary penalty of 60 daily units of Sfr300 (to be suspended pending a probation period).

The captain of RYR 3595 was found guilty in separate proceedings.

The controller appealed to the Supreme Court.


The Supreme Court rejected the appeal.

The court was unpersuaded by the argument of the defence that the lower court was wrong in establishing the facts of the case based on the findings of SAIB's safety investigation.

The Supreme Court reasoned that the controller's conduct was in breach of the relevant ICAO regulations(5) and therefore negligent. The court pointed out that the controller had failed to verify the identity of the crew which had requested a climb to flight level 380. The controller had also failed to realise that the clearance issued was not read back by the RYR 6DW crew for which the clearance had been intended.

According to the court, the controller's failure to act correctly resulted in a collision risk which had endangered the passengers and crews of the two aircraft within the meaning of Article 237 of the Criminal Code. Given the significant loss of the required separation and the TCAS commands for the crews to take evasive action, the collision risk was severe and real.


Air traffic controller and pilot organisations have sharply criticised the Supreme Court's decision, just as they have in respect of earlier convictions handed down by lower Swiss courts for operational incidents that resulted in neither injury nor damage (for further details please see "Air traffic controller convictions draw criticism").

This criticism is justified. First, the Supreme Court's endorsement of the Federal Criminal Court's approach to establishing the facts by referencing SAIB's report runs counter to the principles of safety investigations following aviation incidents. The sole purpose of such investigations is to determine what went wrong in order to use this information to learn and prevent similar incidents from happening in future. It is not the purpose of any such investigation to establish the facts in order to find criminal liability.(6)

Second, it is difficult to see why the significant loss of required separation and TCAS commands alone suffice to conclude that an actual collision risk existed.

Aside from the question of what constitutes a significant loss of separation, the horizontal and vertical distances between two aircraft at one point in time say little about the collision risk. Key for a collision risk assessment are the actual and predicted 3D trajectories of the conflicting aircraft over time – an actual collision risk exists only if the trajectories will possibly meet. There was no such finding in the instant case.

Similarly, the issuance of TCAS commands says little about the collision risk. The current version of the TCAS equipment onboard the conflicting aircraft communicate with each other and will, if certain requirements are met, command a climb RA to one aircraft and a descend RA to the other. Every airline pilot is trained to immediately comply with any such TCAS RA, which is highly likely to resolve the conflict.

Accordingly, the crews of RYR 3595 and TAP 706 quickly followed their TCAS commands and resolved the conflict.

Under these circumstances, a realistic assessment should have concluded that the actual collision risk remained within reasonable bounds. The better view would have been that there was no "danger to the life and limb of other people" within the meaning of Article 237 of the Criminal Code.

Third, the Supreme Court's decision is at odds with the 'just culture' concept, which establishes that aviation professionals should not be punished for actions, omissions or decisions taken by them that are commensurate with their experience and training, but does not tolerate gross negligence, wilful violations or destructive acts.(7)

While the air traffic controller made a mistake, his mistake arguably does not amount to gross negligence or other unacceptable behaviour. The just culture concept works only if aviation professionals are given broad protection against criminal prosecution and conviction. The Supreme Court's decision makes it difficult for aviation professionals to treat their mistakes as learning opportunities. This is a major step backwards for aviation safety.


(1) Judgment 6B_1220/2018.

(2) Final Report 2211.

(3) The ICAO categories are as follows:

  • A – Risk of collision: the risk classification of an aircraft proximity in which a serious risk of collision has existed;
  • B – Safety not assured: the risk classification of an aircraft proximity in which the safety of the aircraft may have been compromised;
  • C – No risk of collision: the risk classification of an aircraft proximity in which no risk of collision has existed; and
  • D – Risk not determined: the risk classification of an aircraft proximity in which insufficient information was available to determine the risk involved or inconclusive or conflicting evidence precluded such determination.

(4) Judgment SK.2018.1.

(5) See Paragraph, Annex 10 of the Chicago Convention and Paragraph of ICAO Doc 4444 on Procedures for Air Navigation Services.

(6) See page 2 of SAIB Report 2211, Paragraph 3.1 of ICAO Annex 13 and Article 24 of the Swiss Air Navigation Act.

(7) See EU Regulation 376/2014, which Switzerland adopted by virtue of the EU-Swiss Air Transport Agreement.

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