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B738, Mumbai India, 2018
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On 10 July 2018, a Boeing 737-800 (VT-AXT) being operated by Air India Express on a scheduled domestic passenger flight from Vijayawada to Mumbai as IX213 marginally overran the wet landing runway 14 at destination after a stabilised approach was followed by a deep landing and the failure of one of the thrust reversers to deploy. With assistance, the aircraft, which was undamaged apart from tyre wear attributable to excessive braking and had remained on a paved surface just 5 metres beyond the end of the runway, was able to taxi to its assigned parking gate for passenger disembarkation.
An Investigation was carried out by the Indian DGCA Directorate of Air Safety in accordance with the Aircraft (Investigation of Accidents and Incidents) Rules 2017. Data from both the CVR and the FDR were successfully downloaded and together enabled a detailed reconstruction of the flight.
It was noted that the 44 year-old Captain had joined the operator as a trainee First Officer before being checked out as a Captain just under three months prior to the event under investigation. He had been PF for the flight and had a total of 3,491 hours flying experience, all but 283 hours of which were on type. The 62 year-old First Officer had joined the operator as a trainee First Officer in 2008 after a 30 year career in the Indian Air Force and was released as such 18 months later. After 5 years as a First Officer, he began command training but failed and continued as a First Officer. He had a total of 8,140 hours total flying experience which included 5,354 hours on type.
The flight, which followed a Mumbai-Vijayawada flight operated by the same aircraft and crew, proceeded normally prior to beginning descent. Inbound, it was noted from the Mumbai ATIS that the surface wind was 250° at 10 knots and that runway 27 was in use. However, soon after descent started, ATC advised that the landing runway would be the 2,471 metre-long runway 14 as per a NOTAM (which had not been included in the pre flight briefing pack supplied to the crew) which advised of an imminent one hour closure of runway 27 for maintenance access and the approach was set up and re-briefed accordingly. Considering the landing would be on wet runway, maximum autobrake was set.
The approach to runway 14 at Mumbai was stable and the AP was disengaged for a flap 30 landing at 450 feet agl. The flare was commenced at 50 feet agl but then lasted 14 seconds and touchdown in moderate rain did not occur until 963 metres past the runway threshold and when the thrust reversers were quickly selected, only the right one deployed. The First Officer immediately called the failure and the Captain cancelled reverse, reduced the thrust of both engines and commenced manual braking, asking the First Officer to assist. The aircraft overran the end of the runway by approximately 5 metres before coming to a stop still on a paved surface and undamaged apart from the two left main gear tyres having been worn beyond limits after excessive braking and, with assistance, it was subsequently possible to taxi to the assigned arrival gate.
Once the engines had been shut down, the CVR CB was tripped and an attending engineer saw that the no 1 engine inboard thrust reverser was stuck in mid position. After manually stowing it, a ground thrust reverser cycle was performed and, although thrust reverser operation was normal, both sleeves were intermittently lagging in operation and the inboard reverser was getting stuck mid-way during the stow cycle which would explain why the reversers had performed normally on the earlier arrival at Vijayawada.
It was noted that the landing had been made in the presence of a significant tailwind component which would not have been present on runway 27 and which was also almost 500 metres longer. It was also observed that the required landing distance had been calculated using the lower tailwind that was being reported at the time the calculation was made. It was also found from FDR data that the engine thrust was only marginally reduced when the flare was commenced and was not further reduced until just before touchdown (at 9 feet agl). The combination of excess thrust and the tailwind component served to prolong the flare and led to a touchdown well beyond the TDZ with almost 40% of the runway behind the aircraft. The corrective actions which followed the unexpected asymmetric reverser deployment were considered appropriate.
It was noted that the whist the crew had expected the runway surface to be wet, they had only realised that the runway was contaminated with water patches after touchdown and that on perceiving that the rate of deceleration was less than needed, it was considered that their decision to use maximum manual braking had been correct. The Investigation also considered that it was likely that dynamic aquaplaning had occurred for up to 5 seconds prior to the disconnection of the autobrake and had contributed to the distance it had taken to bring the aircraft to a stop.
Overall, it was considered that the CVR showed that flight deck CRM had been good throughout the flight.
Thrust Reverser Fault
It was found that following a flight from Dubai to Mumbai the previous day, the crew had made a Technical Log defect entry stating that on the landing roll, the no 1 engine reverser had “stuck at interlock” but after recycling, it functioned normally. After a system function test was unable to replicate the fault and a BITE check found no system fault, the aircraft was released to service and the fault did not recur until landing back at Mumbai the following day after which the fault was rectified by replacement of the thrust reverser middle & lower actuators.
The Cause of the event was determined as “the prolonged flare wherein nearly 40% of the available landing distance was consumed (before touchdown) followed by the failure of the no 1 engine thrust reverser due to defective thrust reverser middle & lower actuators”.
Two Contributory Factors were also identified as follows:
- Dynamic aquaplaning.
- The prevailing weather conditions.
The Final Report was completed on 14 March 2019 and subsequently published. No Safety Recommendations were made.