On 21 April 2016, a Fokker F50 (OO-VLF) being operated by VLM on a scheduled international passenger flight from Berlin Tegel to Friedrichshafen as VLM22TX and a Piper PA28 (OK-ELL) being privately operated under VFR on an international passenger flight from Brno to Friedrichshafen were involved in a near mid-air collision at 4,000 feet QNH approximately 10 nm north east of their destination in day VMC. Minimum separation after the initiation of lateral avoiding action by the F50 was 0.5 nm laterally and 100 feet vertically. Both aircraft subsequently completed their flights without further event.
An Investigation was carried out by the Swiss Transportation Safety Investigation Board (STSB) after notification of the event by the Belgian AAIU and delegation of the investigation responsibility by Germany on the basis that the event occurred in airspace for which the Swiss ANSP Skyguide was, by agreement, responsible for providing ATS. It was noted that the management of the airspace over the region of Friedrichshafen is shared by three ANSPs. The German DFS has delegated ATS over German territory around the Friedrichshafen CTZ to the Swiss ANSP Skyguide but the Austrian ANSP Austro Control provides ATS within the CTZ. The German Federal Air Traffic Controlling Office (BAF) is responsible for “the supervision of these civil ANSPs”.
Relevant data recorded on both the FDR and CVR installed on the F50 were overwritten but relevant QAR from the aircraft were available. It was noted that immediately after the F50 had completed its flight to Friedrichshafen, its Captain had telephoned the VLM OCC to request that the CVR should be “safeguarded for a possible investigation” but the accountable person for the technical division in VLM Flight Operations had refused saying that provision of a replacement device would have delayed further scheduled service by the aircraft that afternoon. This same person was apparently “of the opinion that the CVR had not recorded radiotelephony communications anyway”. The Investigation noted that “as a consequence, the recordings of the conversations between the pilots as well as the sounds emitted by the TCAS on the flight deck were not available, resulting in the loss of a detailed evidence base”. It was also noted that the applicable MEL permitted up to 8 subsequent flights within the following 72 hours without a CVR provided the FDR was functioning normally during this time.
Special ATS arrangements were in place because of the expected significantly higher than normal air traffic expected in connection with an annually held trade fair. These procedures were fully notified to pilots and all controllers involved received special training prior to their implementation. They included a requirement for all aircraft wanting to use the airport except those operating scheduled services to obtain prior permission to do so.
It was noted that the F50 Captain, born in 1976, had 7,000 hours total flying experience which included 6,500 hours on type and that the F50 First Officer, born in 1987, had 750 hours total flying experience which included 550 hours on type. The PA28 pilot had 831 hours total flying experience including 47 hours on type. The APP radar controller had been qualified to operate that position since February 2015 and had one previous experience of working during the annual trade fair which always involved special ATC procedures. Both TWR controllers had over 15 years ‘experience including duties during the periods of special ATC procedures used during the annual trade fair.
It was established that with VMC prevailing, runway 24 was in use at Friedrichshafen. The F50 was being vectored by APP radar onto the runway 24 ILS from the north and the VFR PA28 was in contact with TWR with both aircraft in Class ‘E’ airspace. After responding to an instruction from the TWR ‘VFR Pick-Up’ controller to proceed towards waypoint OSCAR (see the annotated chart below) and being asked whether he would like to land on the paved runway, the pilot responded that he “was going to fly directly to the runway 24 final approach” to which the controller issued a corrective response and told him to remain north of the CTZ which is Class ‘D’ airspace extending up to 4,500 feet (the boundary is shown on the chart).
Meanwhile, the F50 had been cleared by APP radar to descend to 4,000 ft QNH and given a radar heading of 150°. At approximately the same time, the PA28 was reaching the final approach area of runway and at a range of approximately 12 nm from its threshold between 3,700 and 3,800 feet QNH having been re-cleared by the TWR ‘VFR Pick Up’ controller to proceed to final approach via the ILS 24 FAF at an ILS DME range of 8.9nm (this position is within the CTZ). The PA28 had by this time been transferred to the TWR ‘PL-Main’ frequency and on checking in advised his position as ‘on long final’ for runway 24. The PL-Main controller responded by instructing the PA28 to “turn right in the direction of the waypoint ‘OSCAR’ and to remain outside the CTZ” which was correctly read back and the subsequent turn was clearly indicated on the radar recording with the aircraft at approximately 3,900 feet QNH. Although there was a radar display in the TWR, there had been no coordination with the APP radar controller by either of the TWR controllers.
Six seconds after this turn had been initiated (see the annotated chart below) an STCA alert was activated between the two aircraft. Recorded data superimposed on the chart below shows the tracks of the two aircraft involved around the time of their convergence.
The area of conflict with the tracks of the F50 (green) and PA28 (magenta) both coloured red during the STCA activation and their closest point of approach in cyan. A series of almost parallel black lines connects the two aircraft positions as their separation reduced at constant relative bearing as they got closer. [Reproduced from the Official Report]
In response to the STCA alert, the APP radar controller transmitted to the F50 “there is....VFR traffic on your uh one o'clock three and a half miles at 3900 feet coming opposite now, confirm you have him in sight?”. They responded to the controller that they did not have visual contact with the reported traffic and the controller then transmitted “turn right uh disregard the traffic is now crossing right to left one mile in front same altitude“. The APP controller then observed on his radar display the F50 turning right and the PA28 turning left then back to right and “determined that neither a reliable heading instruction nor a descent clearance were possible” as the aircraft was already flying at the 4000 feet MVA.
The F50 crew later stated that prior to the near collision, they had seen the PA traffic at the same altitude on their TCAS traffic display and had been awaiting further instructions when a TCAS TA was triggered leading them to expect an imminent TCAS RA but this had not occurred. They also stated that although VMC prevailed, “visibility from the flight deck had been degraded due to glare resulting from the (relative) position of the sun”. It was subsequently established that in the absence of a TCAS RA, and without ever being able to establish visual contact with the PA28, the F50 Captain had “decided to initiate an avoidance manoeuvre and had turned the aircraft 90° to the right". The F50 crew subsequently reported having observed a relative vertical separation value of +100 feet on their TCAS display during the turn.
At approximately the same time as the F50 was turning right, the TWR PL-Main controller transmitted to the PA28 “traffic is a Fokker 50 on, eh, being established on the ILS a moment ahead of you” and a few seconds later received the response that the pilot had visual contact with that traffic. The F50 Captain subsequently informed the APP controller he had carried out an avoidance manoeuvre and, whilst doing so, had “seen a single engine low wing aircraft which appeared to have been on a collision course with the minimum distance between the two aircraft estimated to have been between 300 and 500 metres”.
Both aircraft subsequently continued to a landing without further event and after completing the flight, the F50 Captain contacted the VLM OCC by telephone and “requested the safeguarding of the CVR so that the event could be investigated” but it was subsequently established that this request had not been met.
The main concern of the Investigation was the ‘operating concept’ on the basis of which the special ATS arrangements made for the busy traffic consequent upon the annual trade fair were based. It was noted that visual approaches to the paved runway 24 “are carried out via the mandatory reporting waypoint OSCAR, north of the airport, with a recommendation to follow the approach corridor at an altitude no higher than 4,000 feet QNH” and that this involves VFR traffic approaching from the south-east crossing the runway 06/24 extended centreline. It was considered that the absence of an altitude limit in the area of the flight corridor as well as outside the CTZ, “an increased concentration of mixed traffic north-east of the airport is to be expected when IFR approaches via a right-hand base for runway 24 take place simultaneously” as in the investigated event. It was noted that during normal (non trade fair) operations, provision exists to geographically segregate VFR and IFR traffic and observed that the prevailing management of airspace around Friedrichshafen Airport has the effect of “complicating and/or precluding the rapid implementation of a practical procedure” for the busy period associated with the annual trade fair.
The Cause of the investigated Serious Incident was formally attributed to “a dangerous convergence of two aircraft flying on a converging course in Class ‘E’ airspace during an aviation exhibition, during which time a commercial aircraft flying under instrument flight rules was in contact with approach control while a light aircraft flying under visual flight rules was in radio contact with aerodrome control”.
It was further identified that the following six Contributory Factors, documented in chronological order, collectively facilitated the dangerous convergence:
- The operational concept consisting of the simultaneous approach of traffic under visual and instrument flight rules during the trade fair entailed systemic risks.
- The pilots of both aircraft were not in radio contact with the same air traffic control unit.
- The traffic guidance within the aerodrome control service concerning the light aircraft approaching under visual flight rules was coordinated inadequately.
- The traffic alert and collision avoidance system on board the commercial aircraft did not generate a resolution advisory due to a lateral avoidance manoeuvre.
- The traffic information provided by the aerodrome control to the pilot of the light aircraft was given too late.
- The pilots of both aircraft only acquired a late visual contact of each other.
In addition, a general Contributory Factor was identified as “the current classification (E) of the airspace in which the dangerous convergence took place”.
One Safety Recommendation was made as a result of the Investigation as follows:
- that the German Air Traffic Controlling Office (BAF) should, in cooperation with the German ANSP (DFS), the Swiss ANSP (Skyguide) and the Austrian ANSP (Austro Control), examine the extent to which the operating concept applied during the aviation exhibition at Friedrichshafen could be improved upon.
It was noted that no Safety Action had been taken since the occurrence of the investigated Serious Incident.
The Final Report of the Investigation was completed on 10 July 2018 and subsequently published online on 1 October 2018. The conflict was classified as a Category ‘A’ AIRPROX.