India Express B738 at Tiruchirappalli on Oct 12th 2018, impacted localizer antenna and wall on departure, captain's seat reclined during departure roll at 117 KIAS

Last Update: July 25, 2021 / 11:17:01 GMT/Zulu time

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Photo of Air India Express VT-AYD, Boeing 737-800 — Air India Express VT-AYD, Boeing 737-800 (Photo modified based on photo from
Konstantin von Wedelstaedt
/ Wikimedia Commons / License: GNU FDL 1.2)

Incident Facts

Date of incident
Oct 12, 2018

Classification
Accident

Airline
Air India Express

Flight number
IX-611

Departure
Tiruchirappalli, India

Destination
Dubai, United Arab Emirates

Aircraft Registration
VT-AYD

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

Airport
Tiruchirapally Civil Airport Airport, Tiruchirappally

Airport ICAO Code
VOTR

An Air India Express Boeing 737-800, registration VT-AYD performing flight IX-611 from Tiruchirappalli (India) to Dubai (United Arab Emirates) with 130 passengers and 6 crew, departed Tiruchirappalli's (also known as Trichy's) runway 27 at 01:18L (19:48Z Oct 11th) but impacted the localizer antenna runway 27 and damaged the wall protecting the localizer antenna runway 27, located about 305 meters/1000 feet past the runway end. The aircraft continued the climb to FL360 and was enroute over the Arabian Sea about 500nm west of Mumbai (India) when the crew was informed about the accident, turned around and diverted to Mumbai. The aircraft landed on Mumbai's runway 09 about 4:15 hours after departure. There were no injuries, the aircraft sustained substantial damage to the belly of the aft fuselage.

The airline reported officials of Trichy Airport informed the flight crew that the aircraft may have come in contact with the airport perimeter wall. The crew, unaware of any anomaly, responded that all systems were working normally. It was however decided to turn around and divert to Mumbai as a precaution. The captain had 3600 hours of flight experience on type thereof 500 in command, the first officer had 3000 hours of flight experience on type. India's DGCA have opened an investigation, both pilots are suspended pending the investigation. A replacement aircraft with a new crew is going to continue the flight.

India's DGCA opened an investigation.

Airport police reported the compound wall at the localizer antenna was 5 feet (1.5 meters) high.

NOTAM A2770/18 suggests the localizer antenna will not be back in operation before Jan 12th 2019.

In 2021 India's DGAC released their final report concluding the probable cause of the accident was:

The probable cause of the accident is “Delayed take-off due to reduction of take-off thrust N1 from 98 % to 77 % before reaching V1, inability of both the crew members to monitor the thrust parameters and to take timely corrective action. This resulted in tail strike and subsequent hitting of the localizer Antenna and boundary wall of the airport.

Contributory factors:

- PIC seatback recliner mechanism failure during take-off roll.

- Breakdown of Crew coordination during switching between PF, PM and back.

- Loss of situational awareness

The DGAC described the sequence of events:

The aircraft back tracked and lined up on runway centreline at the beginning of runway 27.

All checklists including the Before Take-off checklist were completed prior to commencement of Take-off. Thrust levers were advanced and TOGA was pressed when engine N1 reached 40 %. The PIC called for setting take-off thrust. Co-Pilot checked and verified that the take-off thrust was set and called out T/o thrust set, which was acknowledged by the PIC. When the aircraft speed reached ‘80 knots’, Co-Pilot gave out the call and the PIC cross checked it on his PFD.

PIC stated that during high-speed segment of take-off roll, at around 110-115 knots (as per DFDR it was 117 Knots), his seat recliner collapsed and he lost his balance. Both his hands were displaced from the control column as well as thrust levers. The DFDR records thrust reduction from 98% to 77%. The PIC immediately handed over the controls to Co-Pilot by calling out loud ‘Your Controls’ and as per him it took approx. 5 seconds to regain the correct seating position by adjusting collapsed seat recliner. After PIC recovered from the disbalanced position, he looked outside and realised that they are left with last 2000 feet of runway and aircraft still had not attained V1 speed of 143 Kts. The PIC took over the controls while the speed was close to V1 and aircraft was at 1000 feet to go marker, PIC pulled the control column aft to commence the rotation. Crew felt that aircraft rotation was slower and the force required on the control column was higher than normally required. In addition, they also experienced minor vibration during lift off which was described similar to wake turbulence. Once the aircraft was airborne, Co-Pilot called ‘positive rate’ and landing gear up command was executed.

Both cabin crew, stationed at L2 and R2 (rear stations), observed that aircraft acceleration had reduced while it was on take-off roll on the runway and the aircraft took off at a comparatively low height. Further, a thud sound which they perceive was due to baggage shifting in the aft cargo hold, was heard by both cabin crews. They communicated the same to Senior Cabin Crew (L1) after the seat belt sign went off in the cabin.

The duty officer ATC , Trichy observed on NAV aids status indicator that ILS localizer indication has turned red. The CNS was immediately informed to check the status of localizer and report.

CISF security guard stationed near crash gate (P6) heard a sound at around 1950 UTC.

Immediately, he passed the message to their control room that it appears that M/s Air India Express aircraft, during take-off, might have touched the boundary wall or fence and some smoke was also observed in the nearby area. Subsequently, the CISF control room intimated ATC, Trichy.

Once the aircraft got airborne and attained 400 feet height, PIC gave call out ‘HDG SEL’ and same was executed by Co-Pilot, the flaps were retracted, autopilot was engaged and aircraft followed the departure clearance and continued to the climb on track to destination.

At 1954 UTC, Trichy ATC informed crew that “while departure aircraft crossed at the end of Runway at very low altitude”. ATC asked the crew to confirm all ops normal. Subsequently, crew reported all operations normal.

At 1956 UTC, ATC Trichy passed the additional information to crew that “Fire Station reported that at the end of Runway 27 compound wall is broken”. Crew transmitted “OPS NORMAL AXB611”. NOTAM No. A 2266/18 was issued at 1959 UTC regarding unavailability of localizer facility at Trichy airport.

At 2001 UTC, crew requested ATC Trichy “can you come up with what happened”. Crew were apprised that “while you take off, you hit the localizer and boundary wall and localizer antenna broken”. Thereafter, crew replied that “ok sir copied thank you”.

The crew requested HAL ATC to level out at FL 210 so that aircraft speed could be reduced up to landing gear operational speed limit and landing gears could be checked for extension & retraction operation. During landing gear operational check, no abnormality was found. The crew also checked the other aircraft systems including pressurisation system, hydraulic system and engine parameters. It was observed that all the systems are normal and engine parameters were within the limits. Crew informed ATC about normal operations and continued their climb.

Once the aircraft reached its cruise flight level of FL360, the crew once again checked the hydraulic system pressure and quantity, Engine parameters and cabin pressurisation. At FL360, crew observed that pressurisation system of the aircraft was able to maintain differential pressure of 7.9 and cabin altitude of around 7000ft, which was normal as per FCOM. Hydraulic pressure and fluid quantity for both system A and B were checked. Pressure displayed in the cockpit was 3000psi, which was normal. As per the crew, engine parameters were completely normal.

As per the statement of Senior Cabin Crew (SCC), after the seat belt signs were off, cockpit crew called her inside the cockpit to confirm whether they felt any vibration or abnormal noise during take-off phase. The SCC informed the crew that during take-off roll, cabin crew stationed at L2 and R2, heard a thud sound which they perceive as some cargo having shifted as the aircraft pitched up. In addition to this, SCC also passed the information that aircraft speed got reduced once at the time of take-off roll. However, no other abnormality was observed in the Passenger Cabin.

Crew after taking into consideration that no abnormality was observed in any of the aircraft system or parameters and cross verification with SCC on the cabin status, decided to continue the flight to the destination.

At about 2024 UTC, Operator’s AME was called on site for inspection. He identified and confirmed that the broken VHF antenna and honeycomb structure debris present near the localizer antenna belongs to their aircraft. Thereafter, AME informed IOCC and briefed that there might be a possibility of severe damage to the aircraft based on his observation of the accident site.

While the aircraft was close to Muscat FIR point -TOTOX, crew were contacted by Mumbai ATC on HF communication and information was passed that M/s Air India Express wants the aircraft to be diverted to Mumbai. Crew checked the fuel and found that fuel available on board for landing was close to diversion fuel to Pune. Crew informed Mumbai Area that they would be able to land at Mumbai only if direct BBB route will be assigned to them. Crew were instructed to standby. Crew continued the flight to Dubai perceiving that if there would be any delay in response from Mumbai Area, in that situation they could have insufficient fuel for diversion.

While the aircraft was near waypoint TOTOX, Muscat ATC established VHF contact with the crew. Muscat ATC informed the crew that their company wants them to divert to Mumbai. The crew assessed the fuel requirements and checked with Mumbai Area for direct routing to BBB.

Muscat ATC confirmed that requested route was assigned and aircraft was directed to descend to FL350 and turn for a direct routing to BBB (Mumbai). Figure 2 indicates progress of flight after take off.

Crew requested Mumbai ATC for a straight in ILS runway 09 approach with full runway 09 and positioning of firefighting equipment as a precautionary measure on arrival. During approach to Mumbai, landing gears and flaps were extended early to check for normal operations and were found to operate normally.

The aircraft landed on runway 09 at Mumbai airport at 0008 UTC on 12/10/2018, exited via N5 and taxied into bay K6L. Normal deplaning of passengers was carried out and no injury was reported.

The captain (32, ATPL, 4,295 hours total, 4,045 hours on type) was pilot flying and was assisted by a first officer (51, CPL, 4,204 hours total, 3,884 hours on type) as pilot monitoring.

The DGCA analysed:

To establish the serviceability of PIC Seat, inspections and test were done at the OEM facility. After carrying out functional/ operational check on the seat, it was established that recline system of the seat was not locking in position and could be moved with minimal force due to incorrect adjustment of the cable assembly recline. However, after the adjustment of cable assembly-recline, the seat back moved fully & freely between stops and while the control lever recline was released, seat was locking in position. Furthermore, this functional check was repeated several times and results were found satisfactory.

During the inspection done on 12th October and 14th October 2018 at Mumbai, the force required to operate the Recline & Recline control lever was not recorded following procedures as laid down by the OEM. Therefore, the outcome of inspection at OEM facility is considered for this investigation report.

Last 75 Flight Hours/ 15 days Check was carried out on 9th Oct 2018 at Mangalore base and the operation was found satisfactory. In addition, before departure from Dubai & Trichy, the seat was operated by the crew and no discrepancy was recorded. However, these checks only cover the functional elements. The integrity checks of the mechanism is not covered in any of the maintenance schedules prescribed by the manufacturers. Whenever such a defect is recorded, either the provision of MEL are invoked or the seat is replaced with a serviceable one.

Thus, it is clear that recline mechanism failed during take off roll without any prior defect.

...

The PIC was PF from the start of take off roll as established by PIC statement and the left side column force signal, which registered a larger magnitude relative to the right side’s signal in the DFDR. In accordance with the take off procedure, the PIC as PF would have his left hand on the control column and his right hand on the thrust lever. At 117 knots the PIC seat reclined causing the PIC to fall back and become unsettled. Review of PIC statement, DFDR data, Simulator Assessment & Boeing Anthropometric study establishes that a momentarily aft control column pressure was applied and both thrust levers retarded from take off thrust of 98% to 77 % due to PIC hand grip position. The PIC announced your controls and handed over the aircraft to the copilot who now becomes PF. Since the Auto Throttle is in Throttle Hold mode above 84 Kts, the Auto Throttle is no longer commanding thrust requirements. The servos are disconnected and the thrust levers remain in their new position. The FMA displays THR HLD after 84 Kts till N1 is engaged after take off. As a result the airplane’s acceleration is reduced due to the thrust decrease, which can be observed in the speed and longitudinal acceleration parameters which is observed in the DFDR and remained till the aircraft was airborne.

The Co- Pilot while assuming the PF duties did not factor the PIC being momentarily incapacitated due to inability to perform function. As per Boeing FCTM, in the event of Incapacitation the pilot assuming the control must ensure all control levers and switches are in the correct position. In doing so, the co-pilot would be expected to detect the reduction of thrust, announce the abnormality and adjust the thrust levers back to take off thrust.

The co –pilot’s inability to restore the thrust may stem from the fact that the combination of events experienced were unanticipated. The Co-pilot carried out the PF duties by maintaining directional control and exerted positive pressure on control column as seen from DFDR.

The PIC adjusted his seating position and assumed controls by announcing “my controls”.

Subsequent to this the PIC assumed the PF duties and the co-pilot reverts to PM duties. At this moment neither crew member has observed the reduction in thrust for takeoff as the focus is now on the end of runway approaching and the rotation speed not having been achieved. At this stage, a rejected take off was no longer an option. With approximately 2000 feet runway remaining, the PIC exerts aft control column pressure to initiate the take off rotation. The PIC observed the rate of rotation & control forces were higher than normal and the same was corroborated with DFDR data. Computed airspeed at the initial rotation was 145 knots, consistent with the computed rotation speed (VR) of 144 knots.

During the simulator assessment replicating the incident flight, scenarios for recovery were assessed. The results are as below:

1. The Co-pilot rejects Take off 5 seconds after 117 Kts: the reject manoeuvre was possible with adequate margin. This was also established based on the Boeing performance analysis without the 5 second delay.

2. PIC Rejects Take Off after resuming PF Duties: The Reject manoeuvre resulted in an overrun.

3. PIC advances thrust to Max rated with 2000’ of runway remaining (B737 QRH windshear manoeuvre): Take off with adequate margin was possible. There was no tail strike or excursion from the paved surface.

From the above it is concluded that:

- Had the PIC announced “Reject” after announcing “your controls”, as he was unsettled, a reject take off manoeuvre could have been carried out safely by the Co-pilot.
- Had the PIC advanced the thrust to maximum rated (forward stop) on assuming controls, the aircraft would have got airborne safely. (since no derate take off thrust was used)
- Had the PIC rejected take off assuming controls, the aircraft would have overrun.

The reduction in longitudinal acceleration caused by the thrust reduction led to the liftoff point being later than what is expected for the normal take off performance for given conditions.

The PIC experienced slower rotation rate and higher control column force required than normal.

The same is corroborated by the DFDR data and subsequent inputs from Cabin Crew. The PIC increased the control column force aft in order to get airborne. This caused a higher rotation rate, a pitch angle of 10.7 degrees leading to tail strike on the undulated soft surface for 17 meters followed by aft fuselage contacting the localizer antenna and boundary wall as the aircraft pitch was 11.4 degrees. This is corroborated by increase in vertical acceleration from the DFDR.

Based on the above information, the crew were aware that their take off initiation was later than normal. The crew also felt light turbulence as they got Airborne. This perception of turbulence was due to the aircraft contacting the localizer Antenna and the boundary wall and would have lasted for few seconds as stated by the crew and corroborated by the DFDR.

Shortly after the aircraft was airborne, ATC Trichy advised the crew that the:

- take off was low as observed from CISF watch post located near the boundary wall.

- compound wall was broken as advised by Fire Station

- aircraft hit the localizer and Boundary wall and localizer antenna broken. (This was in response of crew query as to what had happened)

The crew decided to carryout system confidence check by levelling at FL 210. This included Hydraulic, Landing Gear, Pressurisation and Engine Parameters. At the time of this check all parameters were found to be normal as per the crew statements and corroborated with the DFDR.

Given the information available to the crew based on their observations and subsequent ATC communication, the probability of structural damage should have been ascertained. Had the crew recognized the possibility of structural damage from the information available to them, it is likely that they would consider not pressurizing the aircraft and accessing a suitable airport for landing. The B737 QRH for tail strike also requires the crew to not to pressurize the aircraft and land at nearest suitable airport.

A Comprehensive decision making Model should have been used to effectively address the threat and error management. The crew’s decision to continue to destination was based on confidence checks alone.

Related NOTAMs:
A2766/18 NOTAMN
Q) VOMF/QMRXX/IV/NBO/A/000/999/
A) VOTR B) 1810111959 C) 1810121000 EST
E) ILS RWY 27 NOT AVBL DUE LLZ ANTENNA BROKEN BY AIRCRAFT HIT

A2767/18 NOTAMR A2766/18
Q) VOMF/QMRXX/IV/NBO/A/000/999/
A) VOTR B) 1810112139 C) 1810121000 EST
E) ILS RWY 27 NOT AVBL DUE LLZ ANTENNA BKN BY ACFT HIT

A2768/18 NOTAMR A2767/18
Q) VOMF/QISXX/IV/NBO/A/000/999/
A) VOTR B) 1810111959 C) 1810121000 EST
E) ILS RWY 27 NOT AVBL DUE LLZ ANTENNA BROKEN BY ACFT HIT

A2770/18 NOTAMR A2769/18
Q) VOMF/QISXX/IV/NBO/A/000/999/
A) VOTR B) 1810120023 C) 1901121000 EST
E) ILS RWY 27 NOT AVBL DUE LLZ ANTENNA BROKEN BY ACFT HIT

Metars:
VOTR 112100Z 00000KT 5000 BR FEW018 SCT100 27/25 Q1007 NOSIG=
VOTR 112030Z 00000KT 5000 BR FEW018 SCT100 27/24 Q1007 NOSIG=
VOTR 112000Z 00000KT 5000 BR FEW018 SCT100 27/24 Q1007 NOSIG=
VOTR 111930Z 00000KT 5000 BR FEW018 SCT100 27/24 Q1008 NOSIG=
VOTR 111900Z 00000KT 5000 BR FEW018 SCT100 28/25 Q1008 NOSIG=
VOTR 111830Z 20002KT 5000 BR FEW018 28/25 Q1008 NOSIG=
VOTR 111800Z 19003KT 5000 BR FEW018 28/25 Q1008 NOSIG=
VOTR 111730Z 19003KT 5000 BR FEW018 28/25 Q1008 NOSIG=
VOTR 111700Z 20003KT 6000 FEW018 28/24 Q1008 BECMG 5000 BR=
VOTR 111630Z 19004KT 6000 FEW018 29/24 Q1008 NOSIG=
VOTR 111600Z 20003KT 6000 FEW018 30/24 Q1008 NOSIG=