THY B738 and Austrian F100 at Geneva on Mar 31st 2014, high risk of collision on runway

Last Update: December 13, 2016 / 16:35:15 GMT/Zulu time

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Photo of THY Turkish Airlines TC-JGV, Boeing 737-800 — THY Turkish Airlines TC-JGV, Boeing 737-800 (Photo credit: airlines470 / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Mar 31, 2014

Classification
Report

Airline
THY Turkish Airlines

Flight number
TK-1919

Departure
Istanbul, Turkey

Destination
Geneva, Switzerland

Aircraft Registration
TC-JGV

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

A THY Turkish Airlines Boeing 737-800, registration TC-JGV performing flight TK-1919 from Istanbul (Turkey) to Geneva (Switzerland), was on final approach to Geneva's runway 05, communication with tower in English was established.

An Austrian Airlines Fokker 100, registration OE-LVL performing flight OS-582 from Geneva (Switzerland) to Vienna (Austria), was cleared to line up runway 05 and wait when TK-1919 was 7.5nm before the runway threshold, communication with tower was performed in English.

Reduced runway separation was in use requiring a minimum separation of 2400 meters between the aircraft.

Tower had advised OS-582 to be number 2 in the departure sequence, an intersection departure from taxiway Z would depart first, and cleared the Fokker 100 to line up runway 05 and wait. He then cleared the private aircraft for takeoff from runway 05 intersection with taxiway Z communicating in French and was waiting for the private aircraft to fly sufficienty clear of the runway for the Fokker 100 to depart, but realized that TK-1919 closed up. He therefore instructed the private aircraft to climb to 5000 feet at best rate of climb, instructed the Fokker to climb to 4000 feet initially, instructed the Boeing to slow to minimum speed possible (which was promptly followed by the crew recognizing the closure and reconfiguring their aircraft to permit for the slowest approach speed possible), turned the private aircraft onto a heading of 010 degrees after it had passed GVA VOR, then cleared OS-582 for takeoff when TK-1919 was 2.2nm before the runway threshold. The RIMCAS runway safety net activated issuing a visual only alert, which was not noticed by the controller who was looking outside. The controller assessed that it was safer to have TK-1919 continue landing and OS-582 continue takeoff than having TK-1919 go around and OS-582 reject takeoff.

Switzerland's SUST reported that when TK-1919 crossed the runway threshold, the Fokker 100 was just about to become airborne and was 1206 meters ahead of the Boeing, a high risk of collision existed. Three seconds after the Fokker became airborne, the Boeing touched down on runway 05.

Switzerland's SUST released their final report concluding the probable causes of the serious incident were:

The serious incident is attributable to the dangerous convergence of an aircraft on take-off and an aircraft in landing phase, on concrete runway 05 because of the inappropriate integration of a take-off from intersection taxiway Z.

The investigation identified the following factor playing a systemic role in the serious incident:

- the parameterisation of the RIMCAS system (Runway Incursion Monitoring and Conflict Alert Sub-System).

The SUST reported the aerodrome controller (39) was well rested and in good health, there was no indication that fatigue played a role in the occurrence.

The SUST analysed that the controller realized at a late stage, that he could slot the private aircraft between a previous departure and the Fokker 100 due to the wake turbulence classes, but had not planned to do so. When he permitted the private aircraft to line up and take off, he did not follow requirements preventing a line up from taxiway Z due to the presence of the Fokker 100, that had already lined up runway 05 at the threshold. In addition the requirement of a maximum 90 seconds between line up and takeoff clearance (for the Fokker 100) was not met.

The starting point of the serious incident was thus the decision to introduce the relatively slow private aircraft into the final phase of an arriving and a departing Category 3 twin jet aircraft. When the controller instructed the private aircraft to use their best climb and turn left only after GVA VOR delayed the possible takeoff of OS-582. In addition, the stress of the situation led the controller to believe the convergence was ended earlier, however, at that point the difference in speeds between TK-1919 and OS-582 was still 55 knots, only 14 seconds later the convergence of the two aircraft ended.

With respect to RIMCAS the SUST analysed:

The RIMCAS system is based on the concept of time which an aircraft will take to go to the closest point of approach in the same manner as onboard collision-avoid-ance systems. Nevertheless, unlike the latter, it does not provide any indication in order to ensure separation between two conflicting moving objects.

Although it is specified to controllers that the RIMCAS system only constitutes an aid to detecting conflicts, the investigation indicates that if it was specifically pa-rameterised for conditions other than those of low visibility, this safety net would be more effective. Measures to be taken in relation to correctly calibrated RIMCAS alerts could then be drawn up. As an example deriving directly from the serious incident, an aural phase 1 alert would have drawn the controller's attention to the fact that a limit had been exceeded.

The SUST commended the flight crew of the Boeing: "The flight crew of flight THY1QM promptly obeyed the speed reduction instructions issued by the controller."

The SUST analysed that the RIMCAS issued an "orange" alert, which only shows a visual message but does not include an aural alert, when in fact the alert was equal to a "red alert", which would issue both a visual and an aural alert. The aural alert would have provided additional cues into decision making by the controller.

The SUST concluded their analysis stating:

The potential dangers inherent in such an incident arise from the distance, now insufficient, between the two aircraft. If the flight crew of the aircraft on final ap-proach ascertains that an aircraft is still on the runway, they may decide to go around and enter into conflict with the aircraft which is taking off. If on the other hand they decide to land and the aircraft on the runway aborts its take-off, the convergence may become highly critical.

The report issued a safety recommendation to review the parameters of the runway RIMCAS system and the alert levels, so that RIMCAS becomes effective also in weather conditions other than low visibility.