KLM Cityhopper F70 near Sylt on Apr 19th 2012, near collision

Last Update: September 19, 2013 / 16:29:40 GMT/Zulu time

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Incident Facts

Date of incident
Apr 19, 2012

Cause
Near collision

Airline
KLM Cityhopper

Aircraft Registration
PH-KZI

Aircraft Type
Fokker 70

ICAO Type Designator
F70

The Dutch Onderzoeksraad (Dutch Safety Board DSB) released their final report reporting, that the separation reduced to 0 feet vertical at 1.1nm lateral separation, 200 feet vertical at 0.59nm lateral and 512 feet vertical at 0.39nm lateral and a risk of a collision existed, and concluding the probable causes of the near collision were:

The aircraft proximity occurred because a fighter aircraft (F-15C ) participating in a military exercise passed an active airway on which an airliner (Fokker 70) was flying at approximately the same altitude. After the responsible fighter controller noticed the conflict situation between both aircraft he unintentionally aggravated the situation by turning the fighter towards the airliner. This resulted in the fighter aircraft crossing the airway again in front of the airliner at the same level.

A loss of separation occurred between the Fokker 70 and the F-15C. The minimum lateral distance between both aircraft was 0.39 NM with a vertical separation of 512 feet.

During the preparation of the air force exercise it was assumed by the exercise staff who organised the exercise that the assigned German airspace was available for the exercise without restrictions. As a result no adequate measures were taken to ensure separation between participating and non-participating traffic. During the first two days of the exercise, after civil traffic had been observed in the exercise area, the staff did not take adequate action to avoid this to reoccur.

Contributing factors were:

- The Royal Netherlands Air Force performed a risk analysis for the total exercise. However the increase in available airspace above FL240 in Germany was not sufficiently seen as a risk.

- The German authorities, which were involved in the preparation of airspace matters for the air force exercise, had the duty to inform the exercise staff about the characteristics of the airspace concerned in their country and the presence of airways. This was not done sufficiently. The exercise staff had the duty to gather more information about the airspace concerned. This was neither done.

- The actions of the fighter control coordinator, who was responsible for the coordination tasks and application for the airspace for the exercise, were not checked thoroughly by another member of the exercise staff or somebody outside the staff.

- The location of one of the regen airfields had been planned close to the airway UN873. This was possible because the exercise staff was not aware of the presence of the airway.

- The F-15C pilot did not adhere to the restriction to stay at or below FL320.

- The fighter controller, who had expressed his concerns regarding the conditions of the exercise, was not able to handle the traffic situation, used non standard terminology and lost the ability to support the exercising aircraft with regard to collision avoidance.

Despite several requests, the USAFE refused to answer the Dutch Safety Board questions, relevant to the investigation. This hampered the investigation and, as a result, prevented the aviation system to enhance the level of safety as much as possible to prevent similar occurrences in the future.

The DSB reported that the airline involved removed the TCAS computer from their aircraft and sent it to the DSB for further analysis, the DSB downloaded the data with the assistance of Fokker Services, the computer was subsequently returned to the airline, who sent it to the manufacturer of the unit for calibration. The manufacturer analysed the data, created a report and sent the report to the DSB. In addition the airline provided quick access recorder data and the flight data recorder to the DSB.

The DSB complained severly and repeatedly: "The DSB sent a list with questions to the USAFE (United States Air Force in Europe) for the F-15C pilot involved. However, no answers were provided by the USAFE."

A large military exercise "Frisian Flag 2012" was planned for April 2012, the preparations began in August 2011, the Frisian Flag exercises usually used Dutch Airspace only and were organised by Royal Netherlands Air Force (RNLAF). Due to restructuring within RNLAF more work was being done by less people however.

For the exercise 2012 a large number of participants was expected, the organisers therefore decided to request the use of Danish and German Airspaces as well, agreements were made in the early planning stage though formal permission was granted only one week ahead of the exercise.

In October 2011 a planning conference was held Leeuwarden Air Base, invited were amongst others also Deutsche Flugsicherung (DFS), Coordination and Scheduling Agency (COSA), Coordination Center for Military Airspace Utilisation of Bunderwehr Air Traffic Service Office (COMIL) and Control and Reporting Center Schoenewalde (CRC). However, Maastricht Upper Area Control (UAC) had not been invited to the planning conference, although airspace above FL245 in the responsibility of Maastricht UAC was being used. Neither COSA nor DFS showed up at the planning conference, the DFS explained to the investigation that they didn't see a need as they had spoken to COMIL and the airspace being used was established military training areas only.

Following the planning conference the document "Frisian Flag 2012, Exercise Operation Order" was sent to all the exercise participants. The document however did not contain any information about airways in the area. The document stated: "It stated that although primary Frisian Flag airspace should be clear of non-players, other traffic might be inside the airspace (e.g. emergencies, weather avoidance). In this case, the air traffic control and fighter control units might provide stranger warnings and may restrict operations as deemed necessary."

On April 15th 2012 all participants in the exercise were briefed at Leeuwarden Air Base, the briefing stated, "that all exercise areas would be clear of non-participating traffic, unless this traffic is specifically cleared by a Control and Reporting Centre or an AWACS."

On the days of the exercise participating aircrews received daily briefings except for the F-15C fighter pilots who operated from their home base in the UK. Liasion officers of the USAFE attended the briefings however to forward the briefings to the aircrew in the UK.

During the first and second day of the exercise, which involved German Airspace, civil airliners were observed within the exercise area, all of the airliners were tracking airway UN873. On the third day (April 18th) only Dutch and Danish Airspaces were used.

On April 16th the exercise coordinator contacted COMIL to query about the presence of civil aircraft in the exercise area. COMIL replied that the airliners had been authorized to operate in that area.

On April 17th the exercise coordinated contacted Bremen Area Control and Lippe Radar asking whether there could anything be done to keep such aircraft out of the danger zone. Bremen replied that there was no possibility as IFR traffic on airways would be given priority over and separation to military traffic. Bremen suggested the exercise controllers might ask for a level change for military traffic crossing the airways. Lippe did not provide a reply however contacted CRC to inquire about the nature of the problem and assigned a special working position staffed with an air traffic controller to permanently monitor the military exercise and provide Bremen and CRC with information about general air traffic crossing the area.

According to the Aeronautical Information Package published by Germany the danger zone around Sylt is defined with the lowest boundary at FL245 and the highest at FL350, airway UN873 crosses the danger zone. The AIP states that general traffic along UN873 is given priority handling over and separation to military traffic.

On April 19th the flight of AWACS needed to be aborted due to fumes in the cockpit, so that there was no monitoring by AWACS, as result the whole German exercise area was controlled by CRC.

On April 19th the tops of the clouds reached up to FL310, the visibility at FL350 was thus unrestricted. The USAFE F-15Cs departed for the exercise with their Mode-C altitude reporting transponders activated and without ACAS (TCAS) equipment on board. Upon entering the exercise area they were declared on "high war" belonging to the "red zone" which required them to remain within a block altitude of FL340 to FL360.

11 minutes prior to the conflict the fighter controller called out airline traffic transiting through the exercise area. The (later conflicting) fighter aircraft confirmed they were aware of the traffic but could not de-conflict the civil non-participating traffic and their military opponents based on their altitude restriction. The controller did not respond.

7 minutes prior to the conflict the fighter controller instructed the (later conflicting) aircraft to immediately turn west due to an airliner at FL340 using the term "hazzle west immediately".

Seconds prior to the conflict the fighter controller again instructed the conflicting F-15C to immediately turn west (again "hazzle west immediately") and maintain FL350 due to a stranger (the Fokker 70). The fighter was already turning right onto a heading of 230 degrees, the crew sighted three airliners one of which, the Fokker 70, appeared to be on the same altitude. The fighter pilot assessed there was no immediate risk of a collision, the frequencies were saturated and he had not received a warning of the non-participating traffic before.

The Fokker 70 had departed Amsterdam with the captain being pilot monitoring and the first officer being pilot flying. The flight had been planned to cruise at FL350 and was enroute at FL350 along airway UN873 approaching waypoint TUSKA at the border between Germany and Denmark. The aircraft had already been handed off to Denmark's Area Control Center Copenhagen (ACCC), ACCC confirmed that radar contacted had been established, when 18 seconds later ACCC advised of an unconfirmed radar target 10nm ahead at the 12 o'clock position at FL352. The Fokker captain replied they were visual with the traffic.

Another 30 seconds later ACCC advised the unknown traffic appeared to descend now showing FL351. A traffic advisory activated in the Fokker cockpit followed by a "CLIMB, CLIMB" resolution advisory. The first officer disengaged the autopilot and followed the resolution advisory which changed into "INCREASE CLIMB, INCREASE CLIMB". The captain remained visual with the traffic all time, due to the TCAS climb he saw the F-15s pass slightly left of and slightly below their aircraft. The captain described the conflicting traffic as a "large pale gray fighter" that appeared to take no evasive action. The first officer was focussed on the instruments and did not see the fighter aircraft pass.

At the time TCAS announced "Clear of Conflict" the aircraft had reached FL365. The first officer levelled off, re-engaged the autopilot and descended back to assigned FL350, while the captain informed air traffic control.

The crew did not give special attention to the NOTAM regarding the "Frisian Flag 2012" exercise on the day of the incident flight, the following day in preparation for the return flight they paid special attention to the NOTAM and concluded that the conflict had occurred outside the exercise area, which was located to the west of the airway.

The DSB analysed that in preparation for the exercise an air space planning software had been used, which featured the possibility to display airways, this feature however had not been used. It had been the first time that German Airspace above FL240 had been made available to the Frisian Flag exercises, the checklists of the exercise however had not been adjusted to this possibility. The invitation of Maastricht UAC to the planning conference might have turned the attention to the airways passing through the exercise area.

The DSB stated: "The absence of the expert is remarkable because the Dutch Ministry of Defence had requested a temporary change in â€˜buffer proceduresâ€™ between civilian and military aircraft. Therefore, Maastricht UAC had performed a safety assessment, which was only related to Dutch airspace. It can be concluded that the Ministry of Defence felt only responsible for the consequences of the operational use of the Dutch airspace. It was assumed without verification that the German military and civil authorities would take their own responsibilities." and continued: "The RNLAF did perform a risk analysis for the total exercise Frisian Flag. However the increase in available airspace above FL240 in Germany was not seen sufficiently as a risk." and concluded the part of analysis: "A thorough risk analysis for the use of the exercise area, especially the area above FL240, might have revealed the presence of the active airway."

The DSB stated: "The fighter control coordinator stated that he never had thought about the presence of airways in the German exercise airspace. A reason was that this airspace consisted of danger areas. He had the experience that airways in Dutch and Danish danger areas were always closed after activation of the danger area. He had assumed that this was the same in Germany. However, in Germany airways can be used in an active danger area and in the area concerned airliners have priority over military traffic. Pilots are urgently requested to contact the air traffic control unit prior to entry of a danger area. In this case, the Fokker 70 cockpit crew contacted Maastricht UAC before entry of the danger area concerned."

The fighter coordinator gave testimony that he was present in the briefings when the representatives of COMIL and CRC were present, the presence of airway UN873 however never came up during the briefings. The COMIL representative stated on the contrary, that during the final planning conference the relevant enroute charts and AIP Germany had been presented and airway UN873 was subject of discussion.

The DSB stated: "The DFS stated that during the preparation meeting for the previous Frisian Flag exercise in 2011 the issue of UN873 was discussed with the exercise planners in length, especially the fact that UN873 is an airway without restrictions and could therefore only be closed after a lengthy approval process by the Ministry of Transport. Therefore the existence of UN873 was definitely known in the past Frisian Flag planning processes."

The representative of CRC stated "that it was mentioned during the meeting that the planning for the Frisian Flag exercise had been done in the same way as the year before. This gave him the feeling that the airspace was already known for everyone involved. He also stated that there are many airways inside and outside the exercise airspace which could have become a factor in one or the other way. Analysing their impact would have been a good preparation, according to the expert."

The DSB analyed to the actions of exercise control after civil traffic was observed in the exercise area on the first two days: "A liaison officer of CRC SchÃ¶newalde, who was present at Leeuwarden Air Base during the exercise, informed the exercise staff during the first two days of the exercise that an active airway was present in the exercise area and that civil traffic could be expected. The exercise staff did not pay attention to the message of the liaison officer and it was subsequently not mentioned during the daily briefings. However, after the second day of the exercise all fighter pilots at Leeuwarden Air Base were aware that airlines were present in the exercise area, because it was discussed among them in the briefing room. During the investigation, it has not become clear if the F-15C pilot was informed by the liaison officers about this. On 18 April, the day before the aircraft proximity occurred, the liaison officer of CRC SchÃ¶newalde pointed the presence of airway UN873 to the mission commander of the exercise. However, no action was taken by the exercise staff."

The DSB analysed that a loss of separation occurred at 10:22:58Z when the lateral separation, according to radar data by Maastricht UAC, reduced to 4.7nm lateral and 200 feet vertical. At 10:23:13Z the F-15C crossed right in front of the Fokker at 1.1nm lateral and 0 feet vertical, the F-15C flying in a westerly direction. At the start of the TCAS climb of the Fokker 70 the aircraft were 0.6nm laterally apart, the transponder of the F-15C indicated FL349 and the Fokker transponder indicated FL351. The minimum lateral separation was 0.39nm, the aircraft had reached a vertical separation of 512 feet due to the TCAS climb of the Fokker 70.

The DSB concluded: "There was a collision danger."

The DSB stated: "The occurrence took place within the exercise area of Frisian Flag in the Hannover UIR (EDVV). This UIR is an upper control area between FL245 and FL660 with airspace classification C. General air traffic on airway UN873 inside this area is controlled by Maastricht UAC. State aircraft operated as operational air traffic within the Hannover UIR are controlled by Lippe radar."

The DSB also reported that a less serious loss of separation involving the same F-15C had occurred 8 minutes earlier with a civil Boeing 737-400 at FL340.

The DSB stated in highlighted text: "Two loss of separation incidents occurred between the F-15C and an airliner within the Frisian Flag exercise area. A risk of collision existed between the F-15C and the Fokker 70. The minimum lateral distance between those aircraft was 0.39 NM with a vertical separation of 512 feet."

The DSB reported, that the fighter controller had restricted the F-15C to FL320 or below prior to the first loss of separation, no location for the restriction was given. 5 minutes later, without the restriction having been cancelled, the fighter pilot climbed the aircraft to FL350. This is when the first loss of separation occurred due to the Boeing 737-400 at FL340. 13 minutes later, the restriction to at or below FL320 had still not been lifted, the F-15C was at FL353 and approached airways UN873 causing the second serious loss of separation.

The DSB analysed: "The [fighter controller's] assistant pointed out the approaching conflict situation. The fighter controller was focussed on providing tactical support to several fighter aircraft taking part in the exercise. Subsequently, he instructed the F-15C pilot to proceed to the west immediately and maintain its level. By doing this the fighter controller unintentionally brought the two aircraft at the same level and the aircraft proximity took place. Above the Fokker 70, at the same location on the radar screen of the fighter controller, another airliner was maintaining FL390 and flying in the same direction as the Fokker 70. The two labels on the radar screen with flight information, among which the flight level, of the airliners concerned overlapped and confused the controller."

The DSB continued analysis: "It seems that the fighter controller, who suddenly had to switch from providing tactical support to separating the fighter aircraft from the airliners, had lost the overview at a certain moment and got saturated. There were nine aircraft on his frequency and he stated there was quite some background noise. The controller mentioned that he did not have a lot of experience with big exercise scenarios like this. Two days before the aircraft proximity occurred, he had expressed his concerns to the fighter allocator regarding the conditions of the exercise, i.e. the location of the regen airfield close to an active airway and the airway itself. The fighter allocator had informed the liaison officer at Leeuwarden Air Base about this. This message did not result in any changes."

The DSB analysed: "The fighter controller used the term â€˜hazzleâ€™ several times. This is an old NATO term. According to the controller the term means that a fighter pilot should use maximum performance (speed and g-forces) and proceed in the direction given in combination with the term. The controller learned this term from more experienced colleagues. During the investigation is has not become clear if the F-15C pilot was familiar with this term."

The DSB reported with respect to non-responses by the USAFE: "Via the Chief Accident Investigation of the Royal Netherlands Air Force, the Board obtained the sanitised investigation report of the USAFE." and reported:

"The internal investigation report36 of the USAFE mentions that the airspace altitude restrictions made the mission planning difficult to ensure deconfliction from other exercise participants as well as transiting civil traffic. Another contributing factor was the lack of clarification requested by the F-15C pilot regarding altitude restrictions after a simultaneous call came in. The report mentions the actions of the fighter controller as a third contributing factor. His altitude restrictions forced the Skimmer flight to either be in conflict with transiting airline traffic or blue air exercise participants. Additionally, an abort could have been initiated much earlier in the sequence of events by the controlling agency or any member of the flight to prevent the situation from developing. The report did not contain recommendations."

The internal RNLAF report issued 9 safety recommendations. The DSB stated: "The findings of the Royal Netherlands Air Force correspond to those of the Dutch Safety Board. Therefore the Dutch Safety Board has not drawn up its own recommendations."

With respect to the lack of response by USAFE the DSB analysed:

"Commercial air traffic provides a relatively safe way of transport. One of the reasons for the level of safety that has been reached, is the mandatory investigation of accidents and serious incidents in which airliners are involved. These investigations, following the provisions of ICAO annex 13, are performed only to learn from mishaps and to prevent their reoccurrence. For a thorough investigation and thus the further improvement of safety in aviation, the cooperation of all parties involved is essential. In this case, despite several requests, the USAFE refused to answer the Dutch Safety Board questions, relevant to the investigation (see appendix D). This hampered the investigation and, as a result, prevented the aviation system to enhance the level of safety as much as possible to prevent similar occurrences in the future.

Among other things it has not become clear during the investigation:

- if the F-15C pilot was informed by the liaison officers that civil aircraft had been observed in the exercise area on the first two days of the exercise;
- who was responsible for collision avoidance in the opinion of the F-15C pilot;
- why the F-15C pilot did not adhere to the altitude restriction;
- if the F-15C pilot was familiar with the terms tactical radar assistance and hazzle."