Smartwings A320 at Bourgas on Jul 18th 2017, runway excursion on landing due to hydraulic failure after touchdown
Last Update: February 17, 2021 / 19:41:21 GMT/Zulu time
Bourgas Airport reported the aircraft was off the runway, however, there were no injuries. The airport was closed until the aircraft could be moved off the runway. Aircraft were being redirected to Varna Airport.
On Jul 27th 2017 Bulgaria's AAIU reported the aircraft performed a VOR approach to runway 04. After touchdown, during roll out, the green hydraulic system failed causing the loss of nose wheel steering. The aircraft veered right off the runway and came to a stop about 30 meters/100 feet from the right runway edge with all gear on soft ground. The passengers disembarked via mobile stairs. The occurrence was rated a serious incident and is being investigated by the AAIU.
On Feb 17th 2021 Bulgaria's AAIU released their final report concluding the probable causes of the serious incident were:
- Green hydraulic system failure due to hydraulic leak during approach for landing and as a result failures affecting the aircraft control and performance during rollout after landing.
- Pilot’s incorrect actions in landing phase after touchdown, resulting in inability to maintain the runway centre line direction under conditions of complete failure of Green hydraulic system, as incorrectly use of maximal brakes and full power of right engine reverser, while having a reduced braking effect of the left brakes.
- CRM, during a high workload flight phase with multiple technical failures and warning inhibition to the crew by aircraft design, led to wrong decision to continue approach for landing and therefore the crew did not perform an assessment of possible malfunctions of flight controls timely.
The AAIU reported that the flight was uneventful until descending through 1300 feet AGL on approach to Bourgas. The AAIU summarized the following sequence of events:
At 05:46:36 h, at 1292 ft altitude, HYD system page comes on ECAM lower display (SD) and caution message "HYD GREEN RESERVOIR LOW LEVEL" appears on ECAM upper display, listing specific crew actions (ECAM actions). This message remains active for 12 seconds and disappears at 1152 ft altitude. According to crew, after LOW LEVEL disappeared, following a CM1 command “Check systems’ status”, reads out the STATUS page, which shows “NORMAL” . This is confirmed by aircraft recordings at 05:47:16 h (STATUS PAGE appears), as GREEN HYD system had still normal pressure at this time and there were no faulty systems yet due to GREEN HYD system pressure. The pilots decided to continue down on prescribed route with autopilot engaged ON, because the ECAM warnings disappeared and they decided that there was no more need to read and do a relevant checklist.
At 05:47:53 h, at 400 ft altitude and speed of 139 kts, CM1 switches off autopilot AP1. Touchdown on the runway is normal, performed at 05.48:32 h in the normal landing area, 300 meters (1000 ft) from the threshold. The RWY is wet from a recent rain, but the braking action is good. CM2 reports partial (incomplete) activation of the spoilers. The pilot in command selected both reversers ON, but only the right one is activated. It appears a tendency for veering to the right, as in the beginning the RWY centre line direction is successfully maintained with the rudder only. Subsequently CM1, even importing maximal deviations of the rudder, separate (unsymmetrical) use of the brakes and attempting to operate the nose landing gear, fails to keep aircraft within RWY.
At 05:48:52 h and 61 kts the plane leaves RWY uncontrollably at a distance of 1750 meters from its beginning. The brakes and the right engine reverser remain activated at their maximal positions and the aircraft enters the soft ground, facing to the apron. At 05:49:05 h, GSPD = 27 kts, on course 095°, CM1 turns off the reverser and retracts the spoilers. CM2 reports to ATC: "TVS1482 leaving the runway." Aircraft passed 120 m out of the runway on the wet lawn, stopping at 5:49:12 h, about 30 m aside its centre, on course 152°, at a distance of 2006 m from the beginning of the runway. Excursing the runway, the aircraft passes over a few RWY lights, past over a drainage cover and hit a signboard on the ground.
After full stop of the aircraft, the commander orders the passengers and the cabin crew to keep their seats in readiness for emergency evacuation and stops the engines. Subsequently, this command is cancelled and coordinated with ATC and airport emergency services, all people on board are normally disembarked by mobile ladders and transported to the terminal.
The investigation determined (for their first hypothesis that weather contributed to the runway excursion) there was no evidence of any adverse weather that could have explained the sudden variation of the aircraft's path during landing.
The investigation determined that technical factors (second hypothesis) caused the runway excursion, however, pilot error (third hypothesis) escalated the events.
The AAIU analysed:
The Commission accepted that the aircraft was correctly dispatched with one inoperative and deactivated braking device on the left-hand main landing gear (LH MLG) according to A320 MEL Section 01-32 / System 32-42 Normal Braking / Item 42-01 Main Wheel Brake. The pilots were familiarized in advance, as it was confirmed by captain’s signature in TLB, certifying that A/C was taken into account the relevant MEL limitations. This way the aircraft was accepted by crew as airworthy and ready for flight. The restrictions (technical and operational) for admission to a flight in this condition require the following circumstances to be expressly provided:
1) The anti-skid system is operative, and;
2) Nose Wheel Steering is operative, and
3) Affected brake is deactivated or removed, and
4) Both reversers are operative, and
5) Green and Yellow systems are operative on operative brakes, and
6) Tachometers associated with operative brakes are operative, and
7) Flight performance penalty is applied.
The emphasized categorical requirements in points above 2), 4) and 5) have been irrevocably eliminated at the moment of the failure and the loss of „Green” hydraulic system, which means that at 05:46 h., at an altitude below 1900 ft by radio altimeter (Flt Phase 6), the aircraft in this condition has already been in trouble regarding the normal control, requiring particular attention by the crew. The short (12 s) appearance of ECAM warning signal during the final approach, at a altitude between 1292 ft and 1152 ft, was ascertained by the crew and the messages in the relevant ECAM pages HYDRAULIC and STATUS were checked. Crew decides to continue descent instead to cancel approach because of lack of necessity of corrective actions in the control card.
The complete loss of Green hydraulics occurred 35 seconds later, at an altitude of 740 ft, in the "inhibit phase".
After touchdown, the crew noticed partial spoiler activation and no activation of engine No 1 reverser. Only the right engine reverser was activated. Nose landing gear control did not respond.
Both pilots had not taken into account that with the loss of the Green hydraulics, the capabilities for deceleration of the aircraft were only as follows:
- 50% of the left-hand landing gear brake efficiency due to the deactivated braking device No 1;
- 100% braking efficiency of the right-hand landing gear of the alternative braking system;
- the remaining 3 spoilers 2, 3 and 4 (1 & 5 didn’t work on both wings);
- the right engine reverser.
The analysis, focusing primarily on the technical aspects as immediate prerequisites for the occurrence:
Normal landing gear retraction and extension are provided by the Green Hydraulic Power. Yet in the process of extending the landing gear, due to a ruptured flexible hose of RH MLG Downlock Actuator, at a working pressure of 3000 psi, for about 35-40 seconds, the entire contents of "green" hydraulic reservoir was sucked out and dumped into the atmosphere. All landing gears were still successfully extended and were mechanically locked in down position. At 05:46 h, an ECAM Message "HYD G RSVR LO LVL" appears for a few seconds, when the GREEN hydraulic fluid level fell at3.5 lt inside the Reservoir (normal level is 14.5 lt). At this time Pressure was normal and stayed normal until 05:47:24 when a Low Pressure signal occurs because the pump sucked air from the empty reservoir. As the engine pump was the only source of pressure in GREEN hydraulics, at the same time (05:47:24h) a message was emitted about total loss of entire GREEN hydraulics - ECAM Message "HYD G SYS LO PR". All subsequent messages and failures registered in Post Flight Report (PFR) were directly attributable to this major failure, as a critical role in the developments after the touchdown was the loss of nose wheel steering signalled at 5:49 am. - "WHEEL N/W STRG FAULT".
With the loss of "green" hydraulics, the following things got up completely unusable, without any alternative:
- Normal braking system;
- Auto braking system;
- ENG 1 Thrust Reverser,
- Nose Wheel Steering.
Primary and Secondary Flight Controls were affected, but they have multiple reservation and aircraft controllability was fully operational.
The landing was performed without nose wheel control, left-hand engine reverser and with availability of only one operational braking device at the left-hand main landing gear. In this configuration, it was evident that with fully engaged right-hand engine reverser combined with 100Z braking at the right-hand main landing gear and about 50Z at left, creates a strong asymmetrical torque to the right-hand direction. An additional factor for this torque was the arm between the right engine and the right main landing gear.
With view to above on the second hypothesis, the following conclusion might be drawn:
The broken hydraulic hose of RH MLG LOCK-STAY ACTUATING CYLINDER resulted in loss of the hydraulic fluid of "green" hydraulics and hence to its complete break-down, resulted in nonoperational state of some systems and controls.
With regard to the third hypothesis - pilot’s mistakes and omissions in flight management:
For the analysis of crew actions, the following was taken into consideration:
- The ASR and statements of both pilots;
- Flight Crew Documents;
- Information about flight time, duty time and crew rests provided by AO;
- MEL - Minimum Equipment List of SX-ORG aircraft;
- Post Flight Report (PFR) - recorded messages and failures;
- DFDR analysis;
- Weather information before and during the flight;
- FCOM, OM, QRH and MEL, related to the aircraft hydraulic systems and their operation.
During the analysis of this hypothesis, the Commission found the following:
- The flight was performed by a standard crew, consisting of a commander and a first officer with the necessary training and experience for the functions they perform. Their licenses and medical certificates were valid, issued in accordance with the requirements of EASA. The commander had a total experience of over 13,200 hrs, of which 2850 hrs flown on the A320 aircraft, while the first officer had totally 735 hrs, of which 521 hrs flown on A320.
- Flight proficiency checks and simulator training were performed on a regular basis and in accordance with regulatory control requirements.
- The information provided about working and rests hours showed, that the pilots were planned in full compliance with the requirements of Regulation 965/2012, Subpart ORO.FLT. There were no preconditions for accumulated fatigue having in mind the long rest before flight, the relatively short flight time and the lack of weather and navigational complications.
In the analysis, the crew actions were divided into three phases - pre-flight preparation, flight phase and final phase.
The dispatching of the aircraft with one inoperative and deactivated braking device on a main landing gear affected the aircraft performance, associated with recalculating the required accelerated-stop distance, and required landing distance, without usage of the automatic braking system (AUTO BRAKE) because of lack of requiring efficiency of the systems mentioned above.
The other brake device on the same main landing gear was worn almost completely, but still in affordable limits. Both right-hand MLG brakes were new, installed the previous day. And this means that the braking performance of left-hand main landing gear is 50%, while on the right-hand MLG it is at full 100%. These elements from the external aircraft inspection are mandatory in preflight preparation and the crew did take note of their peculiarities before signing the TLB by the commander, as it should. This state of brakes and the above-mentioned limitations in MEL 32-42-01A should be analysed with increased attention, included in pre-flight briefing, with recalculation of aircraft performance data (weight limits, speeds and required RWY distances), as well unusual aircraft behaviour in case of need of intensive braking.
At the final phase of the flight, after the touchdown, the aircraft had an inoperative reverser at the side of deactivated braking device, and with no possibility to use nose wheel steering. This was not a problem to keep the direction safely, to stop within the runway if the Alternate Braking system was operating normally and if the crew was prepared, that means the crew should analyse the situation, and to perform the necessary actions in a calm straight flight stage according to QRH, OM and FCOM.
According to DFDR analysis, after touchdown the PF attempted to use a full reverse of both engines to decelerate the aircraft and with maximum braking, pressing the pedals in a varying asymmetrical (more braking at LH brake) and symmetrical sequence. As a result of Green hydraulics failure, only ENG 2 Thrust Reverser was activated, which creates a right-hand torque.
The braking moment of both right-hand brakes was also greater than the one of the single left-hand brake device.
This veering moment should be compensated by using:
- the rudder,
- nose wheel steering (which is INOP due to HYD FAIL),
- asymmetrical use of brakes.
The rudder was effective in keeping landing roll direction at a speed higher than 60kts. After that the aircraft started gradually to turn to the right, the piloting pilot attempted split use of braking for a moment with a rudder fully deflected to the left, but left-hand braking device was insufficient to compensate the torque of high effective right-hand brakes and the right-hand engine reverser, still running at maximum reverse thrust. In such a case, the running reverser must be turned off or reduce its thrust and reduce the pressure on the right-hand brakes using the left-hand brake pressure to keep the direction and deceleration. It was possible that pushing again and keeping maximal pressure on right-hand brakes and full thrust of the right reverser, the pilot had tried to decelerate the aircraft more quickly, but this increased airplane veering to the right and predetermines the RWY excursion.
These CM1 actions indicate that the crew was unprepared for such concatenation of circumstances and had no clear idea about LDA. In fact, RWY length is 3200 m and it is enough for normal stopping without intensive use of brakes and without use of reversers. According to the Landing Performance Chart with one deactivated braking device, Actual Landing Distance will rise to 950 meters and the Required Landing Distance will be 1583 meters. Some recalculation was performed by the crew before the flight in accordance with MEL . During the flight and before descent such a scenario also wasn’t considered in details, and they turned out to be unprepared and their actions were subsequently wrong.
In line with the said in the third hypothesis, it could be concluded that the flight crew contributed to escalation of the emergency resulting from the technical failure.
B) 1707180629 C) 1707180820 EST
E) RWY 04/22 CLSD.
LBBG 180700Z 31003KT 280V350 9999 -SHRA FEW030TCU BKN044 18/17 Q1018 RERA NOSIG=
LBBG 180630Z 29003KT 260V350 9999 SHRA FEW033TCU BKN048 18/16 Q1018 NOSIG=
LBBG 180600Z 30004KT 9999 -SHRA FEW033TCU BKN048 18/16 Q1018 NOSIG=
LBBG 180530Z 32007KT 290V010 9000 -SHRA SCT030TCU BKN049 18/16 Q1017 RERA NOSIG=
LBBG 180500Z 34008KT 9000 SHRA SCT030 BKN049 17/16 Q1017 NOSIG=
LBBG 180430Z 03014KT 8000 SHRA SCT030TCU BKN049 17/15 Q1018 TEMPO 5000 SHRA=
LBBG 180400Z 05010KT 5000 SHRA SCT030TCU BKN049 18/15 Q1018 TEMPO 3000 SHRA=
LBBG 180330Z 01012KT 9999 FEW035 BKN049 19/13 Q1017 NOSIG=
LBBG 180300Z 01011KT 9999 FEW033 BKN049 19/13 Q1016 NOSIG=
LBBG 180230Z 36010KT 9999 FEW020 SCT033 BKN049 19/13 Q1016 NOSIG=
LBBG 180200Z 35014KT 9999 -RA FEW020 SCT033 BKN049 19/14 Q1015 RESHRA NOSIG=
This article is published under license from Avherald.com. © of text by Avherald.com.
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