TCAS Alert Avoids Mid-Air Collision During Visual Approach to Malmö

Casualties unknown • Aircraft incident to SE-DSO over Sjöbo, SE

An Avro RJ100 flying under visual approach entered uncontrolled airspace without the crew's knowledge, triggering a TCAS resolution advisory to avoid another aircraft.

What happened

On 13 October 2009, an Avro 146 Series RJ100, registration SE-DSO, was operating a scheduled passenger flight from Stockholm/Bromma to Malmö. While performing a visual approach to runway 35 at Malmö Airport, the aircraft descended through 2,500 feet, inadvertently entering uncontrolled airspace near Sjöbo, Skåne County.

As the aircraft leveled off at 2,000 feet, the onboard Traffic Collision Avoidance System (TCAS) issued two consecutive warnings: a Traffic Advisory (TA) followed by a Resolution Advisory (RA). The system identified a collision risk with an unidentified aircraft flying at 1,200 feet. The flight crew immediately followed the TCAS instructions, maintaining their vertical speed to avoid the other aircraft. The encounter lasted approximately one minute before the aircraft exited the uncontrolled area.

The investigation

The Swedish Accident Investigation Board (SHK) examined the flight path, air traffic control (ATC) radar data, and the navigation charts used by the crew. The investigation focused on why the crew was unaware they had descended below the controlled airspace boundary.

Investigators found that the aircraft's navigation charts, provided by an external supplier, lacked clear information regarding the altitude limits and boundaries of the controlled airspace. Furthermore, while the aircraft was under Instrument Flight Rules (IFR) for the majority of the flight, the transition to a visual approach meant the crew relied on visual references and available charts that were optimized for IFR operations rather than visual boundaries. ATC radar monitoring also showed that the Short Term Conflict Alert (STCA) system did not trigger, as the system was inhibited for altitudes below 1,700 feet and the conflict occurred between aircraft at different levels of airspace control.

Findings

  • The crew was unaware the aircraft had entered uncontrolled airspace due to a lack of boundary information on their onboard charts.
  • The altitude limitations for visual approaches under IFR were not established for this specific sector, allowing the aircraft to descend into uncontrolled airspace without a predefined restriction.
  • The TCAS functioned correctly, providing the necessary warnings and instructions to prevent a collision.
  • The ATC conflict alert system did not activate because the vertical separation and altitude thresholds were not met for the system's trigger parameters.

Probable cause

The incident was caused by the absence of established altitude restrictions for IFR aircraft performing visual approaches in this sector, combined with navigation charts that failed to indicate the boundaries of controlled airspace.

Frequently asked questions

What happened in the 2009-10-13 aircraft accident near Aircraft incident to SE-DSO over Sjöbo, SE?

An Avro RJ100 flying under visual approach entered uncontrolled airspace without the crew's knowledge, triggering a TCAS resolution advisory to avoid another aircraft.

What aircraft was involved and where did it happen?

The accident on 2009-10-13 involved a aircraft, registration SE-DSO, at Aircraft incident to SE-DSO over Sjöbo, SE.

What was the probable cause of the accident?

The incident was caused by the absence of established altitude restrictions for IFR aircraft performing visual approaches in this sector, combined with navigation charts that failed to indicate the boundaries of controlled airspace.

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