Smartlynx A320 at Tallinn on Feb 28th 2018, runway excursion after bad touch and go

Last Update: November 3, 2019 / 22:44:10 GMT/Zulu time

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Incident Facts

Date of incident
Feb 28, 2018

Classification
Accident

Cause
Runway excursion

Airline
Smartlynx

Aircraft Registration
ES-SAN

Aircraft Type
Airbus A320

ICAO Type Designator
A320

On Nov 3rd 2019 the Estonian Safety Investigation Bureau (ESIB) released their final report concluding the probable causes of the accident were:

Causal factors

This accident results from the combination of the following factors:

- The intermittent THSA override mechanism malfunction allowing to cause the loss of pitch control by both ELACs. The repetitive triggering of the ELAC (ELevator Aileron Computer) PITCH faults was caused by the non or late activations of the PTA micro-switches, which were due to the OVM piston insufficient stroke. The insufficient OVM stroke was caused by the THSA OVM clutch unit non-standard friction. The oil in the THSA OVM casing appeared to be with a higher viscosity than defined in the CMM. The higher viscosity might have reduced the friction of the OVM clutch unit, causing the THSA OVM nonstandard friction.

- SEC design flaw allowing for a single event, the left landing gear temporary dedecompression, to cause the loss of pitch control by both SECs. The absence of ground spoilers arming for landing in the context of touch and go's training may have contributed to the temporary decompression of the left main landing gear.

- The training instructor`s decision for continuation of the flight despite repetitive ELAC PITCH FAULT ECAM caution messages. The lack of clear framework of operational rules for training flights, especially concerning the application of the MEL, and the specific nature of operations that caused pressure to complete the training program may have impacted the crew decision-making process.

Contributory factors

- Smartlynx Estonia ATO TM does not clearly define the need for arming spoilers when performing touch-and-go training (ATO procedures not in accordance with Airbus SOP). The fact that there is no clear reference in the Smartlynx Estonia ATO TM Touch-And-Go air exercise section to additional procedures that should be used, in combination with lack of understanding of the importance for arming the spoilers during this type of flights contributed to TRI making a decision to disarm the spoilers during touch and go training enabling landing gear bounce on touch down.

- At the time of the event Airbus QRH did not define the maximum allowed number of resets for the flight control computers.

- At the time of the event Airbus FCTM did not require to consider MEL on touch-and-go and stop-and-go training.

- The oil in the THS OVM casing was with higher viscosity than defined in the CMM. The higher viscosity might have reduced the friction of the OVM clutch unit.

- The aircraft maintenance documentation does not require any test of the OVM during aircraft regular maintenance checks.

- Smartlynx Estonia ATO OM does not clearly specify the role in the cockpit for the Safety Pilot. The lack of task sharing during the event caused the ECAM warnings to be left unnoticed and unannounced for a long period.

- The crew not resetting the ELAC 1. The fact that ELAC 1 PITCH FAULT was left unreset lead to the degradation of the redundancy of the system.

Considering the remoteness of the loss control of both elevators, there is no specific crew training for MECHANICAL BACKUP in pitch during approach, landing and take-off. This condition of the aircraft occurred for the crew in a sudden manner on rotation and during training flight, where the experienced TRI is not in PF role and cannot get immediate feedback of the aircraft behaviour and condition. Despite these difficult conditions the crew managed to stabilize and land the aircraft with no major damage to the persons on board. The crew performance factors that contributed to the safe landing of the aircraft are the following:

- The TRI followed the golden rule of airmanship (fly, navigate, communicate), by stabilizing the aircraft pitch by using the trim wheel and by keeping the aircraft engine power as long as possible;

- The Safety Pilot started to play a role in the cockpit by assisting the TRI and student by informing them about the status of the aircraft and later on taking the role of the PM.

The ESIB reported the aircraft was performing training flights with 2 pilots, the captain (63, ATPL, 24,046 hours total, 13,500 hours on type) acting as training instructor, a safety pilot (34, ATPL, 3,024 hours total, 2,622 hours on type), 4 students and an Estonian CAA inspector on board. At the time of the occurrence a student (43, CPL, 228 hours total, 0 hours on type) was pilot flying.

The ESIB reported each student would do a number of touch and goes, a full stop landing, then the next student would take the right hand seat, fly the touch and gos, and so on. During the exercises the captain would remain in the left hand seat assuming the role as pilot monitoring, the safety pilot was in the first observer seat and the ECAA inspector in the second observer seat. The other students were seated in the aircraft cabin.

The aircraft had joined Smartlynx Estonia's fleet on Feb 10th 2018 and had flown 68 hours for Smartlynx before the morning of the training flights.

During the first three sessions ELAC1 and ELAC2 fault messages were repetitively triggered.

In the first session ELAC1 and ELAC2 messages were triggered twice each, both ELAC1 and ELAC2 were successfully reset each time, the remaining first session was without incident.

During the second session ELAC1 only triggered once, ELAC1 was reset.

During the third session ELAC1 messages were triggered twice, the first time ELAC1 was reset, the second time ELAC1 was not reset and remained in the faulty condition until end of flight and into the fourth session. During the last touch and go ELAC2 also triggered a fault message, ELAC2 was reset.

During the fourth session on the second touch and go, upon touchdown, ELAC2 again triggered a pitch fault message, the FBW reverted to alternate law (because both ELAC1 and ELAC2 were now in fault conditions), the fault condition however was inhibited during this phase of the flight. The instructor called "Rotate" when the aircraft reached rotation speed 130 KIAS again, the student confirmed he was rotating, however, the aircraft did not respond. Although the student pulled 13 degrees nose up on sidestick, both elevators remained in position 0 degrees and remained in that position until end of flight. The nose up input increased to near full deflection, the aircraft lifted slightly off at 152 KIAS and 0.3 degrees nose up pitch, the instructor began to provide nose up inputs prompting a "dual control" aural message, the instructor pressed the priority button and called "I have control".

The ESIB continued to describe the sequence of events:

4. At 15:05:15, the student released the orders on the sidestick while pitch attitude was still 0.3° Nose Up and the aircraft was airborne. The instructor was close to full Nose Up sidestick deflection (this position was kept for 14 seconds) and giving side stick roll position commands +5 and -5 degrees.

Four seconds later, while the aircraft was approximately 950m from the end of the runway 08, flying with the airspeed of 190 kt, at 19 ft, pitch attitude maximum of 2.8° Nose Up was reached, thrust levers were moved to IDLE and the flap lever was moved from CONF2 to CONF1, moving the flaps from conf. 2 to 1+F.

At 15:05:21 the instructor commanded “gear up” and the gear lever was selected to GEAR UP position. Two seconds later the aircraft reached its maximum altitude over the runway – 48ft and started to descend. The pitch attitude was 0.3° Nose Up, THS remained in 1.5° Nose Up position, and thrust levers were set back to TOGA.

While the landing gear was in transit, the aircraft hit the ground with aircraft engines approximately 200m from the end of the runway at 15:05:28 with the vertical acceleration of 2,85 g. The pitch attitude was 0.7° Nose Up. The airspeed was 192 kt. Two seconds after the impact, the airspeed increased to 206 kt, the pitch attitude to 9,1o Nose Up and the aircraft started to gain altitude at 6000 ft/min.

Seven seconds later, a FLAPS LOCKED and an ENGINE 2 FIRE were triggered with a MASTER WARNING and audio CRC. The aircraft was at 337 ft, the airspeed was 207 kt and the pitch attitude 19.3° (reaching its maximum of 21.8° pitch up at 15:05:38).

At 15:05:42, while the aircraft was in climb and the instructor still applying sidestick inputs in roll and pitch axis (and continued doing this until the end of the flight), the safety pilot declared “Manual pitch trim only, manual pitch trim only” (reads from PFD display). The Pitch attitude was 20,4°, and the altitude was increasing. The THS moved to 0.9° Nose Down, when the crew started to control the pitch of the aircraft by moving the THS with the pitch trim wheel and by engine thrust, by moving the thrust levers to 17° and then to IDLE. The pitch started to decrease.

At 15:05:53, the airspeed was 144kt the aircraft reached maximum height of 1590 ft the pitch started to decrease rapidly and the aircraft started to lose altitude.

The aircraft went into a dive, descending at 7200 ft/min. The instructor moved the thrust levers to 42° (TOGA) and five seconds later started to move the THS towards 4.2° nose up. The pitch attitude reached 25.7° nose down before increasing again. The aircraft reached a minimum height of 596 ft at 15:06:04 and normal acceleration reached +2,44 g. During this part of the flight, in addition to the existing MASTER WARNING, audio CRC and warning messages, several TAWS alerts were triggered SINK RATE, PULL UP, TERRAIN-TERRAIN and TOO LOW, TERRAIN.

At 15:06:23, as the instructor managed to stabilize the trajectory of the aircraft at an altitude around 1200ft and airspeed around 155kt by sidestick inputs on roll, and trim and thrust inputs on pitch axis. The instructor asked “Do we have engines” to which the safety pilot replied “We have engine two fire”.

At this point, the aircraft had L+R ELEVATOR FAULT (ELAC 1 PITCH FAULT, ELAC 2 PITCH FAULT, SEC1 and SEC2 lost control in pitch), pitch control in MECHANICAL BACKUP MODE, roll in DIRECT LAW, yaw in ALTERNATE LAW, engines 1 and 2 damaged from the impact, engine 2 on fire, flaps inoperative (FLAPS LOCKED).

At 15:06:29 the instructor declared to the tower “Mayday, Mayday, Mayday” (this call was not transferred to ATC). Seven seconds later, the safety pilot started to read loudly the ECAM display: “So we have flaps lock, flight control law, left right elevator fault, maximum speed 320, manual pitch trim use, do not use speed brakes”. The following 29 seconds the aircraft remained stable at around 1300 ft. The pitch attitude varied between 8° Nose Down and 16° Nose Up, with an average at 5° Nose Up.

At 15:06:58, the instructor declared again to the tower “Mayday, Mayday, Mayday”. The safety pilot took over the conversation by declaring: “Mayday, Mayday, Mayday, we have flight control fail”.

The instructor proposed to turn right, got it confirmed by the safety pilot, and declared it to the tower and informed about making a right turn and visually flying back to the runway.

At 15:07:44 the instructor commanded the safety pilot and the student to change their seats. At this point, the ECAA inspector and the student left the cockpit and were seated in the cabin.

34 seconds later, MASTER WARNING push button was pushed and the CRC ended. The instructor asked “what is the heading of the runway”, safety pilot replied “262” and changed the heading in the FMS.

The safety pilot declared to the tower: “Tallinn Tower, we are going for runway 26” and at 15:08:28 declared engine two fire to the tower and requested for a fire brigade.

Around 15:08:50, the safety pilot suggested moving the engine 2 lever to idle because of the fire. Instructor confirmed, but stated: ”If I am losing (an engine) and manual flying, I prefer (to land) when engines are working”. The thrust lever was moved to idle, but 3 seconds later it was moved back to the previous position to keep the engine working while flying the aircraft manually.

At 15:09:00 the instructor requested: “Gear down”.

At 15:09:19, engine 2 spooled down following a 100 second fire alarm and ECAM message ENG 2 FAIL. The Safety pilot informed: “Engine two is shut down”.

Twelve seconds later, the Instructor stated “Gear is down, flaps three”, to which the safety pilot stated “speed is checked, flaps three”, moving the slat/flap lever to position 3.

At 15:09:39, engine 1 spooled down. Both CVR and FDR stopped recording.

As the RAT automatically deployed, the CVR started recording again at 15:09:54. At this point the aircraft had lost electrical power in buses AC and DC1 and 2, electrical power in RH primary flight display (PFD) and navigation display (ND) and cabin light.

The safety pilot states: ”Gear is down. We don’t have engines” and starts reading the speed indication from the LH PFD to the instructor. At 15:09:56 “Speed 150”, at 15:10:00 “Speed 130”, At 15:10:02 “Speed 120”.

Approximately 15:10:12 the aircraft touched down hardly 150m before the runway threshold, burst all tires, decelerated on the runway and veered off stopping close to the left runway edge (20). During the impact, safety officer and one student suffered minor impact trauma.

All the persons on board evacuated the aircraft using the escape slide.

The ESIB analysed:

During the training flights the aircrafts` F/CTL system triggered several ELAC PITCH FAULTs while the instructor was manually stopping the trim wheel when the THS was returning to 0° after touch down (ground setting).

The investigation revealed that the ELAC PITCH FAULT messages were originated from the intermittent failure of the THSA (Trimmable Horizontal Stabiliser Actuator) OVM (Override Mechanism). The ELAC PITCH FAULT was triggered by the computer in control (ELAC1 or ELAC2) due to erratic signals coming from the PTA micro-switches. The incorrect triggering of the PTA micro-switches was caused by a non-standard displacement of the OVM output piston which, in turn, was caused by a non-standard friction curve of the OVM clutch unit. The oil in the OVM was measured to be with almost twice of the viscosity of the oil required by the manufacturer. The higher viscosity of the oil most probably contributed to having a non-standard friction curve in the OVM clutch unit. The investigation could not confirm this hypothesis it by experiment data nor could determine a documented origin of the wrong oil in the THS.

The fact that the aircraft maintenance documentation does not require any test of the OVM during aircraft regular maintenance checks could have contributed to the result that the wrong oil in the OVM was left unnoticed during aircraft exploitation.

Additionally, as the ECAM caution messages were inhibited during approach, landing and take-off and as they appeared after the aircraft passed 1500 ft, it made it hard for the flight crew to make a link between a hardware failure on landing and a repetitive computer failure messages appearing in level flight. This might have lead them to underestimate the problem as it was apparently solved by a single reset.

The fact that the ELAC 1 was left un-reset by the crew following the last F/CTL ELAC1 PITCH FAULT cannot be fully explained by the investigation. It has to be noted that the F/CTL ELAC 1(2) PITCH FAULT ECAM alert is for crew awareness and therefore has no associated procedure and aural warning. The flight crew can consider a system reset if it is authorized by the QRH system reset table (as for this case, it was). The absence of single chime for this ELAC1 PITCH FAULT situation as per system design, compared to the previous one for which a single chime of unknown origin was concomitant (and that was followed by ELAC reset by the crew) may have played a role in the absence of computer reset by the crew.

With respect to the decision to not continue the go and reject takeoff, the ESIB analysed:

During the event, as the TRI commanded „GO“ at 15:05:03, the student started to move the thrust levers to 42o (TOGA). The levers reached 42o at 15:05:07. At 15:05:13 the TRI discovers that the aircraft is not rotating and takes over the control. By that time CAS was 170 kt, and the aircraft was 1600 m from the end of the runway.

The decision to reject a take-off is normally a rule-based decision with clearly defined failure events and a calculated V1 decision speed. The manufacturer advises that a touch-and-go should not be rejected once TOGA is set, unless the commander is certain the aircraft will not safely fly and notes that there is no V1 decision speed on a touch-and-go.

As for this accident, by the time the TRI realizes that the aircraft is not rotating and as he takes over the control, TOGA power had already been selected and kept for 6 seconds. At this time the crew do not fully understand the condition of the aircraft, and on basis of the normal operational procedures, aircraft speed, location, engine speed, the TRI decides not to reject the take-off.

With respect to crew performance and CRM the ESIB analysed:

At 15:05:13, as the TRI realized that the aircraft does not rotate and as he took over the control of the aircraft, the PFD indicated MANUAL PITCH TRIM ONLY and L+R ELEVATOR FAULT on the ECAM display (and a continuous repetitive chime was triggered at 15:05:10). At that time, no crew member announced the L+R ELEV FAULT and MAN PITCH TRIM ONLY. The fact that initially there was no reaction to the ECAM warning (and the master warning) was probably due to information overload and confusion from the unexpected situation:

- the TRI was performing in performing 2 roles - Pilot Monitoring and as an instructor. Thus the task sharing was different from a normal situation,

- the aircraft control handover and the role change might have caused a delay in understanding the situation,

- the student pilots` performance compared to an experienced pilot was most probably lower in a stressful emergency situation,

- the fact that the aircraft was not responding to the inputs on sidestick might have generated a very high stress in thistime limited and dynamic phase for which actions are normally learned to be executed in a very quick and automatic way,

- the fact that the role of the Safety Pilot is not clearly defined might have caused confusion because the task sharing had to be improvised under a stressful situation.

At 15:05:42 while the aircraft was in climb, the Safety pilot started to read out loud the PFD message “MAN PITCH TRIM ONLY” to attract the TRI`s attention on the flight controls while the TRI and the student shared their lack of understanding of the situation. 36 s after the triggering of these messages the TRI started to control the aircraft pitch by using the pitch trim wheel and engine thrust, however kept applying inputs on the side stick (in all control axis) even it had no effect over aircraft pitch control.

Due to the rare nature of this situation – having the aircraft in mechanical backup during rotation – and the fact that the TRI had to take over the control of the aircraft and to understand the condition of it, caused confusion and the lack of understanding of this situation. The fact that there is no training for the crew for aircraft being in Mechanical back-up at rotation, the TRI had to learn and adapt flying the aircraft in pitch with trim and engine thrust while handling this unexpected situation.

As the role of the Safety pilot was not clearly defined in the ATO OM, the lack of pre-defined tasks and task sharing, led to the need for improvising and taking initiative by the Safety pilot in a very stressful situation, resulting this delay in understanding the situation and taking necessary actions to manage the situation.

After the crew had stabilized the aircraft flight path at 15:06:29 the TRI tried to make radio contact with the ATC tower and declare “Mayday, mayday, mayday”. Due to high workload of the TRI the communication was discontinued and at 15:07:00 the Safety pilot took initiative in taking over the radio communication. During the radio communication with the tower at 15:07:02 the crew made a decision to directly turn back, change the runway in the MCDU, and try to land the aircraft on the opposite runway. During this period the TRI never calls for ECAM actions. The Safety pilot takes initiative in this situation again at 15:06:39 and starts to read out loud the ECAM messages. At 15:07:44 after the command from the TRI, the student pilot and the Safety pilot change seats and the Safety pilot starts to support the TRI in radio communication and as PM.

Although engine 2 indicated fire, and engine 1 indicated oil low pressure issues, the TRI decided to keep the engines running as long as possible (until engine no. 2 spooled down at 15:09:21 and engine no. 1 spooled down at 15:09:38).

The crew actions in managing the prioritization of tasks – following the “golden rule” – fly, navigate, communicate, the initiative from the Safety pilot and the prompt decision to turn back, approach the runway as directly as possible (with the aircraft not being aligned with the runway axis) and keep the engines running as long as possible, enabled the crew to manage this situation, keep the aircraft under control and land the aircraft without casualties.
Incident Facts

Date of incident
Feb 28, 2018

Classification
Accident

Cause
Runway excursion

Airline
Smartlynx

Aircraft Registration
ES-SAN

Aircraft Type
Airbus A320

ICAO Type Designator
A320

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