VIA A320 at Varna on May 24th 2013, runway excursion

Last Update: November 26, 2014 / 17:30:54 GMT/Zulu time

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Incident Facts

Date of incident
May 24, 2013

Classification
Accident

Aircraft Registration
LZ-MDR

Aircraft Type
Airbus A320

ICAO Type Designator
A320

Airport ICAO Code
LBWN

Bulgaria's Air Accident Investigation Unit (BAAIU) released their final report in Bulgarian concluding the probable causes of the accident were:

- Inadequate in depth analysis of the meteorologic conditions in the forecast as well as underestimation of weather observations with respect to the descent of the aircraft by meteorological offices at Varna Airport, Air Traffic Control and the crew of the aircraft
- dynamic sharp changes of wind speed and direction just prior to touch down
- Non compliance with tail wind limits by the crew and incorrect decision by the aircraft commander to continue the landing although current weather conditions required to go around and either enter a hold to wait for better conditions or divert to an alternate aerodrome
- the aircraft touched down at about the mid point of the runway at a speed above Vapp. Automatic brakes were deactivated when the pilot flying applied brakes, who however was late in applying maximum brakes pressure
- Increased workload by the commander due to
~ lack of experience of the first officer
~ time pressure due to next scheduled leg of the aircraft

Contributing factors

- ATIS information between 06:30Z and 07:30Z provided the term "NOSIG" which reinforced the incorrect assessment of the actual weather conditions by air traffic control and crew
- Change of the active runway by air traffic control without consultation with weather offices and without consideration to the fact that the glideslope transmitter of the ILS was operating in "bypass" mode

The BAAIU reported that upon nearing Varna the crew listened to ATIS information "U" at about 06:50Z, which indicated that runway 27 was active and arriving aircraft should expect a VOR approach to runway 27, visibility was at 4500 meters, winds from 230 degrees at 8 knots, rain, cumulo nimbus cloud at 2200 feet, temperature at +19 degrees C, dew point at -16 degrees C, QNH 1002, NOSIG (no significant changes in the next 2 hours).

The captain (54, ATPL, 16,300 hours total, 9,457 hours on type) was pilot flying, the first officer (46, ATPL, 4,980 hours total, 18 hours on type) pilot monitoring.

Upon contacting approach control of Varna the aircraft was cleared to descent to 9000 feet on QNH 1001, the crew read back they were cleared to 9000 feet at 1009 hectoPascals and inquired whether they could perform an ILS approach to runway 09, the controller corrected the wrong readback repeating QNH 1001 which was read back correctly on the second readbach, the crew again requesting an ILS approach to runway 09. After coordination with tower the approach controller advised the crew to expect an ILS approach to runway 09 and provided a vector to a point 10nm ahead of runway 09 and cleared a descent to 5000 feet.

While the aircraft was descending ATIS switched to information "W", which was announced by the approach controller. Information "W" reported active runway 27, arrivals to expect VOR approaches to runway 27, the runway was wet, winds from 240 degrees at 8 knots, visibility 6000 meters, temperature +19 degrees C, dew point -17 degrees C, rain, CB at 2200 feet, NOSIG. Approach reconfirmed the crew could expect the ILS approach to runway 09. The aircraft gets cleared to descend to 2500 feet and subsequently for the ILS approach runway 09 before being handed off to tower.

On a final approach to runway 09, about 5nm before touchdown, the crew contacted tower and received information "variable winds at 19 knots gusting up to 31 knots" and clearance to land on runway 09, the crew acknowledged.

The aircraft was configured for landing with gear down, full flaps, spoilers armed, autobrakes set to medium.

Just as the aircraft crossed the runway threshold at 45 feet AGL at 152 KIAS/187 knots over ground a frontal system arrived over the aerodrome from the southwest associated with significant increase in wind changing from southwest to west and increased rain. The aircraft floats at a height of 8 feet for about 7 seconds and about 1300 meters (runway length 2517 meters), touches down at about 1220 meters of runway left at a speed of 168 knots over ground producing a vertical acceleration of +1.35G. The captain subsequently opened reversers, the spoilers extended into their ground positions, the aircraft however was unable to stop within the remaining runway. The captain steered the aircraft slightly left to avoid a collision with the localizer antenna, the aircraft collided with the airport perimeter fence and came to a stop 224 meters past the end of the runway and 37 meters to the left of the extended runway center line. A burning smell develops in the cabin prompting the commander to perform the fire drills for both engines and order an emergency evacuation via slides. During the evacuation through all exits two passengers received broken ankles and were taken to hospitals.

The BAAIU reported that the crew did not receive a specific TAF indicating variable gusting winds of up to 15 meters/second (30 knots) at about their time of arrival, not before departure from Leipzig nor during flight. Information off the weather radar of Varna Airport show, that a series of strong convective cells were located west of the aerodrome at about 06:50Z, which combined into one large powerful cell moving northeast and reaching the aerodrome with its "wall" just as the aircraft crossed the runway threshold, also reflected in special weather reports issued at 07:13Z, 07:16Z and 07:21Z (also seen in the METARs).

The BAAIU reported that the lawn of the airport was being mowed at the time of the landing to the left of the runway. For this purpose the glideslope transmitted had been put into bypass, the aerodrome engineer monitoring possible deviations of the glideslope as result of the works via a laptop. No deviation was recorded at the time of approach and landing. The lawn mower reached a point sensitive to the glideslope about one minute after the overrun and stopped. The BAAIU conducted tests of whether the lawn mower could have caused unrecorded glideslope deviations during their investigation, setting the glideslope transmitter into bypass and having the lawn mower drive along its path during the accident day, the tests showed no deviation of the glideslope. The BAAIU reported that the "bypass mode" disables the automatic monitoring system of the ILS to switch from the main to the stand by transmitter in case of a disturbance being recorded.

The BAAIU computed the actual landing distance required in the existing wind conditions (more than 30 knots of tail wind amounting to 1080 meters of increased landing distance) at the time of landing was 2606 meters, more than the landing distance available.

The BAAIU analysed that the Vapp of the aircraft was 134 KIAS, it remains unclear why the aircraft was crossing the runway threshold at 158 KIAS, 24 knots above reference speed, therefore. According to tests with the lawn mower a theory of disturbances on the glideslope signal were "untrustworthy", a second theory of malfunctioning aircraft systems found no support in flight data recorder and examination of the aircraft. The third theory suggests that the crew did not react timely to environmental changes.

The BAAIU analysed that the approach to runway 27 would have required 5 additional minutes of flying, at which time the combined large cell would already have been over the aerodrome. The approach to runway 09 however was in line with an aircraft approaching from the west and was equipped with a superior navigation aid, the ILS, apart from saving those 5 minutes additional flying time, which became a factor into the crew decision due to time constraints imposed by the schedule of the aircraft. At the time of the crew deciding for an ILS approach to runway 09 ATIS as well as ATC information both suggested a tail wind component albeit within the operational limits of the aircraft. Additional information like the TAF indicating strong varyiing winds at about their time of arrival as well as amended information about the wind situation from ATC was not available to the crew. Only when the crew checked in with tower, the crew received surprising information about the wind gusting up to 31 knots, even though ATIS and ATC information had suggested "NOSIG" over the next two hours.

The BAAIU continued analysis that at this time the aircraft was about 5nm from touchdown, sufficient time to decide for a go around and assess the options like entering a hold to wait for weather improvement or divert to the alternate aerodrome at Bourgas. The BAAIU analysed that the little experience of just 18 hours on type of the first officer may have put the commander into a difficult position with respect to decide for a go-around. However, computation of the landing distance required in the existing circumstances exceeding the landing distance available required the approach to be aborted, the decision to continue the landing is thus not acceptable.

The BAAIU analysed that the work load of the captain increased substantially on short final forcing him to concentrate on piloting the aircraft rather than assessing the weather scenario and landing distances. The passitivity of the first officer, becoming obvious with the "before landing checklist", contributed to the increase of work load and also led to the first officer not calling deviations from the standard operating procedures, e.g. deviations from the glideslope and particular reference speeds, that would have prompted the decision to go around by the commander. The BAAIU specifically mentions that an additional safety pilot to compensate for the lack of experience by the first officer could have prevented the accident.

The BAAIU analysed that tower changed the runway from 27 to 09 without consulting with weather office and without consideration to the fact, that the ILS' glideslope transmitted was in bypass mode. The BAAIU stated that tower was not required to consult with met offices according to standard operating procedures at the time. This lack of requirement resulted in tower permitting the use of runway purely on ATIS information. There is no provision in the ATC manual about the ILS transmitters being in stand by mode, too. With the transmitter in bypass however it was possible that disturbances of the transmitters/beams would not be corrected.

The BAAIU analysed that tower missed a chance to prevent the accident when an aircraft holding short of runway 09 waiting for departure queried the current winds about 2 minutes prior to the accident resulting in tower reading the winds from 180 degrees at 21 knots showing a large wind change - the wind change was not relayed to the arriving VIA flight however due to time constraints. The omission of this information was in violation of the requirements of ATC manual however.

The investigation analysed that the term NOSIG was not justified especially with the prospect of a TAF released at approx. 04:20Z indicating strong varyiing winds at around 07:00Z to 07:30Z gusting up to 30 knots. This NOSIG however contributed to both tower and crew misjudging the existing weather scenario and not expecting the significant weather change that occurred on very short final to just prior to touchdown.

The BAAIU analysed that the captain declared Mayday and requested assistance by emergency services believing to transmit on tower frequency however talking on Intercom due to stress. Cabin crew acting professionally however did not initiate the emergency evacuation until explicit command to initiate emergency evacuation was given by the captain.

The BAAIU analysed that the captain timely and correctly decided to inititate the emergency evacuation agreeing with the considerations that the damage to the aircraft was unknown, there was smoke in the cabin probably due to the rupture of the oil seal in the right hand engine and dust from the fractured airport perimeter fence. However, the instruction to cabin crew was provided before the actual checklists being read invoking the danger that passengers evacuate with the engines still running and being sucked into the engines. Cabin crew, after receiving the instruction to evacuate, verified that the engines had been shut down before the first passengers left the aircraft.

The BAAIU analysed that the evacuation took about six minutes way above the target of 90 seconds. It took about two minutes from the decision to evacuate until all passengers were off the aircraft due to advanced age of the majority of passengers and decreased mobility of some passengers and an accumulation of passengers near the over wing exits as well as bad weather conditions with reduced visibility, strong winds and rain. It took another 4 minutes for the crew to leave the aircraft after collecting laptops and other personal belongings.

The investigation released a number of safety recommendations to Bulgaria's Civil Aviation Authority to review and improve weather analysis and information flow to ATC and operators to ensure all pertinent data are and become available to flight crew, ensure flight crew know limitations of their aircraft, review procedures to verify operability of navigation aids in particular ILS, improve ATC manuals and improve Crew Resource Management Training during simulator sessions.
Incident Facts

Date of incident
May 24, 2013

Classification
Accident

Aircraft Registration
LZ-MDR

Aircraft Type
Airbus A320

ICAO Type Designator
A320

Airport ICAO Code
LBWN

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