Norwegian B738 and B733 at Bergen on Oct 4th 2011, loss of separation between go-around and takeoff

Last Update: September 10, 2012 / 13:46:42 GMT/Zulu time

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Incident Facts

Date of incident
Oct 4, 2011

Classification
Report

Flight number
DY-1831

Destination
Bergen, Norway

Aircraft Registration
LN-NOP

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

A Norwegian Air Shuttle Boeing 737-800, registration LN-NOP performing flight DY-1831 from Alicante,SP (Spain) to Bergen (Norway) with 179 passengers and 6 crew, was on final approach to Bergen's runway 17 descending through about 500 feet AGL, the commander (ATPL, 6,770 hours total, 4,159 hours on type) being pilot monitoring and another captain (ATPL, 8,850 hours total, 2,850 hours on type) assuming duties as first officer and pilot flying, when the crew decided to go-around after hearing a takeoff clearance. The pilot monitoring slightly stood up in his seat in order to get sight of the departing aircraft and noticed the aircraft at that point had not gone past taxiway A3 and thus expected the takeoff would be rejected.

A Norwegian Air Shuttle Boeing 737-300, registration LN-KKI performing flight DY-1318 from Bergen (Norway) to London Gatwick,EN (UK) with 113 passengers and 5 crew, had taxied to holding point A2 to depart from runway 17. Upon reaching the holding point the crew checked in with tower, who queried whether they could immediately depart. The crew affirmed, and about 50 seconds later, following touch down of an arriving Dash 8 cleared to line up runway 17. The crew acknowledged stating "... line up 17, ready for immediate departure", tower subsequently instructed the landed Dash 8 to expedite vacating the runway. While taxiing onto the runway the crew noticed an aircraft on arrival but nothing out of the ordinary and expected to depart prior to the arrival. About 67 seconds after line up clearance tower cleared DY-1318 for immediate takeoff, the crew immediately accelerated the engines and the aircraft began rolling about 7 seconds after takeoff clearance. When the aircraft was just accelerating through V1 the crew heard the arriving aircraft reporting they were going around.

Both aircraft were climbing out on runway heading, the Boeing 737-300 initially climbing out at 170 KIAS with the Boeing 737-800 already flying at 190 KIAS and closing up. While the arriving aircraft was climbing out tower handed the arrival off to radar. At that time the Boeing 737-300 had just become airborne between taxiways A5 and A6, horizontal distance 0.8nm. Tower immediately handed them off to radar as well, the crew puzzled with the quick hand off queried tower but did not receive a reply and switched to radar reporting there must have been a reason for the quick handoff.

The arriving crew had been busy with the go-around and were satisfied the go-around had gone normal so far, the pilot monitoring thus reported on radar they were going around and climbing straight on runway heading to 4000 feet. Just when he released the microphon button he heard the pilot flying gasp and understood the go-around was anything but normal. The aircraft had just begun levelling off and the pilot flying had thus lowered the nose and got sight of the departing Boeing 737-300 just ahead and slightly below them. The pilot flying immediately initiated a turn to the right.

A few seconds later radar control instructed the arriving 737-800, in order to resolve the conflict, to turn right to heading 280 degrees, which the pilot flying had already initiated prior to the instruction.

The crew of the Boeing 737-800 subsequently observed the distance between the aircraft increasing, radar followed up stopping the climb of the departing aircraft at 3000 feet, and the required separation was re-established.

LN-NOP positioned for another approach and landed safely, the departing LN-KKI reached London safely without further incident.

Norway's Statens havarikommisjon (AIBN) released their final report in Norwegian concluding the probable cause of the serious incident was:

a misjudgement of tower controller, that was not corrected by implementing alternative measures.

Contributing factors were the lack of documented policies for traffic in a go around, the tower controller's limited experience as air traffic controller and limited opportunity for practical training in a similiar scenario.

Three safety recommendations were issued to Avinor, air traffic control service provider.

The AIBN reported the minimum separation between the two aircraft reduced to 400 feet vertical and 0.5nm horizontally according to radar data.

The separation beween the arriving Dash 8 and the arriving 737-800 had been 6.2nm when the tower decided to squeeze the departure between the two. The Dash crew later reported they were astonished about hearing the line up clearance after their touch down and being told to expedite vacating the runway.

The AIBN reported that at the time the takeoff clearance was issued to LN-NOP the arriving LN-KKI was 1.5nm before the runway threshold with an estimated 36 seconds remaining to touch down. About 15 seconds after the decision to initiate the go-around the crew radioed they were going around.

The commander of the departing 737-300 held an ATPL with 5000 hours total experience and 4,260 hours on type, the first officer a CPL with 9,616 hours total and 3,915 hours on type.

The tower controller had been certified on Jun 1st 2011 following 15 months of training. He had been off duty the two days prior to the incident, on the day of the incident he first worked two hours as ground controller followed by one hour of rest, then he assumed duty as tower controller, 35 minutes later the incident occurred.

The AIBN quoted both flight crew reporting that they had no TCAS advisory. The short term collision alert at the radar facility did not activate, the system is configured to alert about pending collisions at or above 5500 feet, both aircraft were below 5500 feet AGL during the conflict.

The AIBN analysed that the controller intended to provide efficient service. However, there was no arrival after LN-NOP and no other departure waiting, so that there was no compelling reason why LN-KKI should depart ahead of LN-NOP.

Standard operating procedures stipulated that the departing aircraft should have begun takeoff roll when the arriving aircraft is one minute ahead of the landing threshold. This would also require at least 2 minutes between arriving aircraft, the distance between the Dash 8 and LN-NOP was 1 minutes 48 seconds. The landing roll and taxi of the Dash 8 took longer than anticipated because turnoff A6 was closed and the aircraft needed to continue to A7 on the runway. The plan by the tower controller therefore left no margins.

The AIBN analysed further that despite the margins proving scarce and reducing further the controller did not invoke an alternate plan like cancelling the takeoff clearance and instruct the arrival to go around and coordinate with departure. Another option could have been to instruct the arriving aircraft "... in case of a go-around turn right heading ..."

The AIBN assessed that the tower controllers assessment to not stop the departure was correct at the time of when the go-around was announced. The departure had already been too far into the takeoff roll.

The AIBN further assessed that the tower controllers decision to not coordinate with radar himself but ask ground control to do the coordination, aggravated the situation. The ground controller had not heard what had happened and thus was not in the possession and did not relay the information of two simultaneous departures.

The AIBN believes the tower controller should have resolved the conflict himself by keeping both aircraft on his frequency and issue vectors to get both aircraft on diverging trajectories.

The AIBN further believes the hand off during the initial stages of the go-around to radar caused unnecessary burden onto the flight crew of LN-NOP.

The AIBN analysed the decision of the flight crew of LN-NOP to go-around was correct because it was uncertain whether LN-KKI would have vacated the runway already before they would touch down.

The AIBN stated their commendation of the flight crew of LN-NOP for their quick and decisive reaction to turn right in order to avoid a dangerous situation.

The AIBN also commended the radar controller stating that he learned about the conflict only through the second phone call now from tower that there were two simultaneous departures. He quickly perceived the conflict and issued correct radar vectors to bring the aircraft onto diverging flight trajectories. The instructions would have come in time to prevent a real danger of a collision.

The AIBN analysed that both TCAS systems probably did not issue advisories due to the low closure rate between the aircraft. A relative speed of 10-15 knots between the aircraft meant a longer time than the set threshold for a traffic or resolution advisory would be needed to a possible collision. Although both flight crews certainly had the conflicting traffic depicted on their TCAS displays it was unreasonable to assume the flight crews would monitor that screen due to the high workload during the go-around and takeoff.

The AIBN analysed that the go-around procedure in effect was the standard departure route and thus does not ensure that IFR traffic is separated from other IFR traffic if a departure and a go-around happen at the same time.

The AIBN analysed that there were no guidelines regarding hand off from tower to departure. Observation in practise showed that the hand off occurred at different times and altitude depending on controller and flight crew involved. Especially there was no guideline regarding hand off or keeping aircraft on tower frequency in case of simultaneous go-around and takeoff.

There had been no guidelines by Avinor for local procedures at Flesland airport, these were developed only following the incident.

The AIBN finally analysed that there was no real risk of a collision arguing that there was good visibility, the aircraft were following each other with a relatively little relative speed, and the trailing crew got sight of the aircraft ahead, despite the fact that separation reduced to 400 feet vertical and 0.5nm horizontally.
Incident Facts

Date of incident
Oct 4, 2011

Classification
Report

Flight number
DY-1831

Destination
Bergen, Norway

Aircraft Registration
LN-NOP

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

This article is published under license from Avherald.com. © of text by Avherald.com.
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