UTAir B738 at Sochi on Sep 1st 2018, overran runway on landing
Last Update: January 18, 2020 / 16:56:54 GMT/Zulu time
The report concludes the probable causes of the accident were:
The aircraft overrun, destroying and damage by fire were caused by the following factors:
- repeated disregarding of the windshear warnings which when entered a horizontal windshear (changing from the head wind to tail one) at low altitude resulted in landing at distance of 1285 m from the RWY threshold (overrunning the landing zone by 385 m) with the increased IAS and tail wind;
- landing to the runway, when its normative friction coefficient was less than 0.3 that according to the regulations in force, did not allow to land.
The factors contributed the accident:
- the crew violation of the AFM and Operator's OM requirements in regards to the actions required a forecasted or actual wind shear warning;
- use of the automatic flight mode (autopilot, autothrottle) in the flight under the windshear conditions which resulted in the aircraft being unstable (excess thrust) when turning to the manual control;
- lack of prevention measures taken by the Operator when the previous cases of poor crew response to windshear warning were found;
- insufficient crew training in regards to CRM and TEM that did not allow to identify committed mistakes and/or violations in good time;
- the crew members' high psychoemotional state caused by inconsistency between the actual landing conditions and the received training as well as the psychological limit which was determined by the individual psychological constitution of each member;
- insufficient braking both in auto and manual mode during the aircraft rollout caused by the insufficient tyre-to-ground friction aiming to achieve the specified rate of braking. Most probably the insufficient tyre-to-ground friction was caused by the significant amount of water on the RWY surface;
- the aerodrome services' noncompliance of Sochi International Aerodrome Manual requirements related to the RWY after heavy showers inspection which resulted in the crew provision of wrong normative friction coefficients.
In obtaining of the increased overrun speed of about ¡Ö75 kt (¡Ö140 km/h) the later setting of engines into reverse mode was contributed (the engines were set into reverse mode 16 s later than the aircraft landed at distance of about ¡Ö200 m from the runway end).
The MAK reported the first officer (53, ATPL, 12,277 hours total, 5,147 hours on type) was pilot flying, the captain (51, ATPL, 13,995 hours total, 6391 hours on type thereof 5,147 hours in command) was pilot monitoring.
The MAK analysed the first approach to runway 06 stating that the aircraft descended through 1000 feet AGL in an entirely stabilized approach. Descending through 850 feet AGL the crew received a predictive windshear aural warning "Go Around! Windshear ahead", the crew however did not react, neither discussed the warning nor initiated a go around, but continued the approach. Descending through the decision height of 627 feet neither pilot flying nor pilot monitoring announced a decision (Continue or GO Around). The aircraft continued the approach. Descending through 170 feet AGL, about 850 meters ahead of the runway threshold, a reactive windshear alert was issued "Windshear! Windshear! Windshear!". Again the crew continued the approach. About 110 feet AGL the first officer asked "See the runway?" at which point the captain took control of the aircraft and initiated a go around due to the runway visibility being obscured by a heavy rain shower. The flight data recorder showed the aircraft descended to 50 feet AGL about 40 meters ahead of the runway threshold before climbing again.
The aircraft climbed above transition level to FL100. The crew subsequently prepared for a second approach in a rushed manner however, for example the captain's altimeter remained set to the standard pressure. While descending through 4500 feet MSL on the second approach tower advised a preceding aircraft had gone around, that crew however did not provide any reason for the go around. The aircraft was flying in LNAV and was on a track parallel to the runway approach path when the crew attempted to activate the approach mode, however, the aircraft did not intercept the localizer and no localizer capture occurred. The aircraft however descended and stopped at 2000 feet (600 meters), the glideslope intercept altitude. While levelling off at 2000 feet the aircraft simultaneously captured LOC and glideslope, and began the descent on the glideslope tracking the localizer. Descending through 1050 feet AGL the crew again received a predicitive windshear alert "Go Around! Windhear ahead". Descending through 470 feet AGL, 2650 meters ahead of the runway threshold, the crew received a reactive windshear alert again "Windshear! Windshear! Windshear!" indicating the aircraft had again entered the zone of windshear, the approach however was continued. In reaction to the windshear autothrottle accelerated the engines. Descending through 75 feet AGL, the aircraft was now in the middle of the windshear and autothrottle began to reduce thrust as the aircraft had accelerated to 170 KIAS (target speed 157 KIAS), the captain disengaged autopilot and autothrust freezing the thrust setting. The rate of descent decreased, the wind changed to a tail wind increasing the speed over ground to 178 knots while the aircraft crossed the runway threshold at 54 feet AGL. The aircraft continued to float for 14 seconds and touched down at 160 KIAS and 170 knots over ground about 1285 meters/4415 feet past the runway threshold. Ground spoilers were automatically extended, and autobrakes (set to MAX) engaged. The first officer announced "Speed Brake up! Reversers Maximum!" however, the reversers had not yet been selected and were selected only 20 seconds later. The captain issued an expletive and demanded "Reversers!". 2690 meters/8820 feet down the runway the reversers were selected, the engines had already spooled down to ground idle, the engines began to accelerate but reached maximum reverse thrust only after the aircraft had already overrun the end of the runway. 13 seconds after autobrakes had engaged the captain queried "is the autobrake working?" the first officer responded with an expletive and "apply braking". The commander applied manual braking disengaging autobrakes that way. Maximum manual braking was applied, no difference in brakes pressure was recorded. 26 seconds after touchdown the aircraft overran the end of the runway at 75 knots over ground, broke through the aerodrome perimeter fence and came to a stop in the Mzymta river bed. A fuel leak from the left hand wing tank started a fire, the passengers were evacuated. Airport emergency services brought the fire under control.
Simulation of the landing revealed that the brakes were working as designed, however, the runway conditions did not match the runway condition report the crew had received (0.5 to 0.55 friction coefficient). The coefficient rather varied between 0.05 to 0.18 leaving insufficient friction to achieve the target deceleration rate. The worst runway conditions were encountered between 2230 and 2560 meters down the runway due to sloping of the runway and water accumulation on the runway.
The modelling and simulations showed that even with a touchdown 1300 meters down the runway with runway friction at 0.5 no overrun would have occurred. However, if the runway is covered by water and the reversers are deployed immediately on touch down the aircraft would overrun the end of the runway by 125 meters, and as in this case with the reversers deployed with delay the overrun was computed at 985 meters.
Boeing concluded that with the actual touch down point it was unlikely the aircraft would have stopped prior to the runway end even if the thrust reversers had been immediately deployed. However, had the aircraft touched down in the touch down zone, thrust reversers been immediately deployed, the aircraft would have stopped on the runway 2400 meters down the runway.
This article is published under license from Avherald.com. © of text by Avherald.com.
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