A Boeing 737 and a Cessna 172 were involved in a serious airprox incident near Falsterbo, Sweden. The Boeing passed the Cessna almost overhead and at almost the same altitude, according to the HCLJ investigation report.
A privately operated Cessna F172K Skyhawk, OY-AKH, with one pilot and one passenger on board, conducted a Visual Flight Rules (VFR) flight from Rønne (EKRN) on the Danish island of Bornholm to Copenhagen Roskilde (EKRK) on the Danish island of Zealand on 20 July 2014.
The other aircraft was an EgyptAir Boeing 737-866 (WL), conducting a passenger flight from Cairo International Airport, Egypt, to Copenhagen Kastrup (EKCH) on the Danish island of Zealand.
Both aircraft passed enroute overhead the southern part of Sweden to their planned destinations.
After departure from Rønne, but prior to reaching Swedish airspace, the pilot of the Cessna contacted Sweden Control and informed that the aircraft had departed Rønne enroute to Roskilde and maintained an altitude of 4,000 feet.
As the Cessna approached Swedish airspace without having requested a permission to enter the controlled airspace of Malmö TMA, the ATCO presumed that it flying below the lower limit of Malmö TMA, as this was common practise among pilots conducting VFR flights from Rønne to other airports in Denmark.
It was the perception of the Cessna pilot, that he had requested and received a permission to enter and cross Malmö TMA.
Furthermore, the pilot believed that the altitude was displayed on radar. Without further radio communication with Sweden Control, the Cessna continued westbound into and through Malmö TMA at 4,000 feet msl, and passed just north of the city of Trelleborg at 13:04:02 hours.
At the same time, the Boeing 737 was approaching the southern coastline of Sweden on a westnorthwesterly course descending through FL082.
At 13:04:30 hours, the EgyptAir flight contacted Copenhagen Approach. The ATCO at Copenhagen Approach issued an instruction to descend to 4,000 msl.
Shortly before the Cessna aircraft passed the boundary between Malmö TMA and Copenhagen TMA, the passenger became sick and vomited in the cockpit and on the pilot’s tablet. This caused some distress in the cockpit and the pilot’s focus diverted from the operation of the aircraft. The pilot’s pre-planned descent, to an altitude below the lower limit of Copenhagen TMA, was delayed.
Meanwhile the EgyptAir flight was maintaining 4,000 feet msl flying with a groundspeed of approximately 285 knots. The two aircraft flew on projected crossing tracks with a converging angle of approximately 25 degrees.
The pilots on board the Boeing 737 observed the Cessna at a horizontal distance of 8 nautical miles in their 2 o’clock position at the same altitude. Subsequently, the pilots had a TCAS TA presentation of the Cessna without altitude indication presented on their navigation displays.
At 13:07:51 hours, the Boeing 737 passed the Cessna at a radar presented horizontal distance of 0.0 nm and seemingly at the same altitude.
The Cessna then showed an increase in ground speed from 110 knots to 150 knots and a 30 degree turn to the right. Speed and course were then regained.
The EgyptAir crew then reported passing the Cessna at the same altitude.
Earlier, the ATCO had noticed the track of aircraft A, but the ATCO presumed that the aircraft was an uncontrolled VFR flight flying below Copenhagen TMA (below 2,500 feet).
At 13:09:32 hours, the Cessna pilot contacted Copenhagen Information informing that he conducted a VFR flight to Roskilde maintaining an altitude of 4,000 feet. The pilot then stated that he would descend to below 2,500 feet. All the time the Cessna’s altitude was not displayed in radar screens. Only after selecting a new squawk for Copenhagen Information did the radar display the aircraft altitude.
The Danish Accident Investigation Board concluded that the following factors played a role in the incident:
- During the sequence of events, ATC and TCAS of aircraft B [the Boeing 737] did not receive mode C information from the transponder of aircraft A [the Cessna 172].
- Due to the passenger becoming sick, the focus of the pilot of aircraft A was diverted from flying the aircraft.
- Unauthorised, aircraft A penetrated Copenhagen TMA.
- A seemingly misperception by the pilots of aircraft B of the horizontal separation influenced their decision on not making an appropriate avoiding action.