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  • Olga Lubryczyńska - Budrewicz


On the evening of July 19, 2020, an aviation incident took place on runway 24R at Palma de Mallorca Airport. During this incident, a passenger aircraft was granted permission for takeoff while a technical vehicle was still present on the same runway. The controller responsible for issuing the permission was operating independently in combined positions mode due to low air traffic at the time. However, the technician conducting the lighting inspection was monitoring the ATC frequency and immediately informed the controller about the vehicle vacating the runway upon hearing the permission given to the crew. Upon receiving this information, the controller promptly aborted the takeoff.

The recommendations presented in the final report highlight the significance of enhancing the training of air traffic controllers in visual observation techniques and the effective using of A-SMGCS radar data. These actions are intended to ensure precise verification of the positions of vehicles and aircraft on the maneuvering area, thereby preventing the reoccurrence of similar incidents in the future.

It is important to note that none of the recommendations and suggestions regarding the incident specifically referred to either suspending or withdrawing the operation of the combined position procedure including SPO (Single Person Operation).

Additionally, it should be mentioned that a supervisor was present in the ops room at the time of the incident, but his involvement in other tasks made it impossible for him to detect the error.

Based on the available press information, a similar incident took place at one of the Polish airports in February 2021. During this incident, a controller working alone issued clearance for landing while a maintenance company vehicle was present on the runway. However, the controller quickly recognized the conflicting clearance and immediately aborted the approach, instructing the crew to go around.

The article describing the incident stated that "(...) the tower ATCO performed alone combined duties of a controller and an assistant." The article highlighted that the controller independently managed the unplanned landing of the Wizz Air Airbus, while simultaneously making phone calls, having to coordinate with the second on duty at Pyrzowice Airport, contacting the approach controller in Krakow, and keeping radio correspondence with the flight crews. According to the articles statement, the absence of an assistant eliminated the additional safety barrier by the "four-eye rule," in which a second person monitors the air traffic situation and can help identify errors. During the incident, a trainee who could have been used as an assistant was on a break after a three-hour on-duty period. The article highlighted the importance of the "four-eye principle" (4EP) as a key principle in aviation.

Various definitions

Finding a safety rule in aviation documentation that specifically mentions the "four-eye rule" (4EP) proved to be a difficult challenge. Based on available information, the principle is commonly associated with financial risk management. It can be interpreted as an internal control mechanism that requires every action of a person in an organization involving a material risk to be reviewed or verified by a second independent and competent person. The purpose of the control is to reduce the risk of errors, such as negative consequences resulting from improper performance of routine business tasks or internal fraud.

In aviation-related materials, this principle appeared in reference to the Germanwings plane crash on March 24, 2015. Indeed, the European Union Aviation Safety Agency (EASA) recommended European airlines to implement the "four eyes" (4EP) principle in the cockpit during all phases of flight. This means that if one of the pilots leaves the cockpit, the presence of another crew member (a flight attendant) is required in the cabin to observe the remaining pilot. The intention behind implementing this principle was primarily to prevent the possibility of a pilot barricading themselves in the cockpit. Regardless of the additional person's role in the cockpit, which should be defined in crew procedures, especially in emergency situations, it is difficult to expect the present flight attendant to detect pilot errors...

In air traffic control, the "four eyes" (4EP) principle appears as a "best practices" recommendation developed by the International Federation of Air Traffic Controllers' Associations (IFATCA). One of the Federation's main goals is to promote the interests of air traffic controllers. IFATCA provides guidelines and recommendations to its member associations but does not establish binding rules or regulations.

The Federation, which represents controllers from across the globe, regularly hosts conferences that serve as a platform for air traffic controllers to share their experiences. It collaboratively develops best practices and promotes safe working principles within the profession, aiming to recommend their implementation. During one of the conferences in 2005, where air traffic controllers reported safety hazards related to Single Person Operations (SPO), it was recognized that the minimum staffing for an operational position in air traffic control "should consist of more than one ATCO" (Air Traffic Control Officer). As a result of these findings, a recommendation was made to introduce the 4EP definition and promote this principle by the association's members and social organizations of air traffic controllers from different countries as a safety barrier.

The "Four Eyes Principle" developed at that time, refers to a situation where an active controller is accompanied by another appropriately qualified controller whose function includes monitoring the same work area as the active controller. The association's controllers have highlighted the necessity of exempting air traffic controllers from responsibility in incidents or accidents that occur due to the non-implementation of the 4EP principle, either fully or partially. However, up to this day, none of the mentioned assumptions have been incorporated into legal regulations.

Two-persons teams

The use of two-person teams in air traffic control organizations, especially in radar positions, particularly in Area Control Centers (ACC), is a fact. However, the essence of such work organization is not to monitor one controller's work by another but rather to create conditions for increased efficiency in ATC units with high traffic volumes by dividing tasks into an "executive" controller and a "planner" controller. In this configuration, the "executive" controller executes the plan prepared by the partner but also possesses a certain "independence" that allows them to act differently from what the "planner" assumed, based on their license and privileges.

The practice of having another controller monitor the performance of an individual's accuracy takes place only in situations involving the supervision of an instructor over a trainee or during assessments by an assessor, as specified in EU regulations. In all other cases, the controller is solely responsible for his or her decisions, air traffic control clearances, instructions given to aircraft crews, coordination with other air traffic services and units and other tasks performed while in an operational position.

Why pretend?

According to aviation law, a member of the aviation personnel is a person who holds a valid license and is registered in the state register of aviation personnel. The license serves as a certificate confirming specific qualifications and authorizing the individual to perform designated aviation tasks. There is no specific legal definition of aviation tasks. Therefore, it can be understood that aviation tasks are the responsibilities assigned to air traffic controllers as outlined in operational instructions.

It seems rather inappropriate to delegate these tasks to unlicensed personnel, such as assistants. Although some institutions employing ATCO may have provisions in their operational manuals that allow delegation to other unlicensed staff members, it is clearly stated that the air traffic controller retains ultimate responsibility for these actions. While such practices are recognized and accepted by aviation authorities, they involve inherent risks that must be identified and mitigated through appropriate measures.

The acceptability of such practices should be a subject of discussion, while given the potential risks.

Air traffic controllers, as licensed personnel, bear full responsibility for carrying out aviation tasks. Relying on non-qualified personnel to independently perform aviation tasks seems inappropriate, particularly in terms of monitoring their work and detecting errors. Such an approach could imply that tasks derived from the license do not require the competence of an air traffic controller.

Given the 4EP rule, it is important to emphasize that it is the controller who brings the rule into force and is used as an additional safety barrier for flight crews. While a controller on the ground can leave the position at any time, the flight crew, fully responsible for flight safety, is obligated to perform aviation tasks from takeoff to engine shutdown, relying on the "second pair of eyes" provided by well-trained air traffic controllers.

An air traffic controller's license is the evidence of successful completion of training and the ability to handle heavy traffic situations. Before being licensed for independent operational work, each controller must demonstrate the necessary skills, including handling emergency and unusual situations without the assistance of an assistant or another air traffic controller. Lack of operational self-directed skills will disqualify a candidate.

Decisions regarding operational planning, flight level and route are the responsibility of the pilots. The flight crew determines the actions to be taken in dangerous situations. In this case, the controller plays an advisory role, coordinating the reported concerns and expectations of the flight crew with other relevant units.

Must not remain silent

Air traffic management institutions are service providers whose main objective is to ensure the safe and efficient provision of air traffic control services to airline operators. Given the fees charged for these services, the management of air traffic services should be run in a cost-effective and operationally efficient manner.

Implementing the "four-eyes" principle, as suggested by IFATCA, can be expensive because it requires obtaining more resources, which are costly and not easily accessible. Air navigation service providers may hesitate to reduce their staff, especially when there is low air traffic and one controller is capable of handling the workload. However, due to pressure from social organizations and following recommendations, they may still maintain higher staffing levels and opt for costly solutions. It is important to avoid such a situation and have thorough discussions about it. Effective resource management involves ensuring that the money paid by airlines for the services is utilized appropriately.

Based on information received from Eurocontrol, "successful efforts are being made to reduce the cost per service unit. One way of reducing costs comes from providing ATCOs with the systems to enable them to handle more traffic. In order to achieve 16 million flights per year by 2050 (compared to the 11.1 million seen in 2019), it will be necessary for ATM systems to change quite significantly. The operational concept is for a move towards business-driven trajectories, updated and deconflicted in real time, with the role of ATCOs evolving towards monitoring most flights rather than actively controlling them. A great deal of work is in hand to move toward this objective".


In recent years, the aviation industry has been facing multiple crises, and as a result, airlines have been actively seeking ways to reduce costs. One significant factor driving the exploration of "single-pilot cockpit" operations is the predicted increase in pilot shortages in the coming decade. Recognizing this, EASA (European Union Aviation Safety Agency) has presented a preliminary concept to ICAO (International Civil Aviation Organization) to enable reduced crew operations.

The initial concept focuses on implementing single-pilot operations during the en-route phase, while the second concept considers the possibility of a full flight being piloted by a single person. The European ATM Master Plan also mentions the introduction of "single-pilot operations" as a result of advancements in air traffic management solutions that allow for greater autonomy of the aircraft crew.

However, the implementation of "single-pilot operations" will require aircraft manufacturers to invest in the development of onboard systems and technologies. This development could involve a significant investment. EASA anticipates that these changes will result in both safety benefits and long-term cost savings.


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