What aircraft was involved and where did it happen?

The accident on 2017-09-04 involved a B-737-800, registration VT-AYB, operated by Air India Express Ltd., at COCHIN AIRPORT, IN.

What was the probable cause of the accident?

The accident was caused by the pilot's incorrect decision to initiate a turn before the intended taxiway link, exacerbated by poor visibility during heavy rain, low light conditions, and pilot fatigue.

Boeing 737 Excursion into Rainwater Drain at Cochin Airport

A Boeing 737-800 operated by Air India Express veered off taxiway C and into an open drain during heavy rain, causing significant structural damage.

What happened

On the night of September 4, 2017, an Air India Express Boeing 737-800, registration VT-AYB, was taxiing at Cochin International Airport following a flight from Abu Dhabi. During the taxi phase, the aircraft made an unplanned left turn approximately 90 meters before reaching Taxiway F. This maneuver caused the aircraft to exit the paved surface of Taxiway C and enter an open rainwater drain.

The impact of the excursion caused the nose landing gear to collapse. As the aircraft continued forward, the main landing gears also entered the drain, leaving the engines and the rear belly of the aircraft as the primary weight-bearing components. The pilot attempted to use engine thrust three times to pull the aircraft out of the ditch, but the aircraft remained stuck. Passengers were eventually evacuated via a step ladder from the L1 door. While there were 3 minor injuries among the passengers, no fatalities were reported.

The investigation

AAIB India investigators examined the cockpit voice recorder, flight data, and local meteorological conditions. The investigation established that the aircraft had landed late on Runway 21 due to heavy rain, which necessitated vacating the runway via C2 rather than the usual C3 exit.

Investigators also reviewed the visibility conditions, noting that while the weather was rainy, the taxiway centerline was nearly impossible to see. The investigation looked into the crew's coordination, noting that the co-pilot had requested a "Follow Me" jeep and advised slowing down due to poor visibility, but the pilot-in-command did not respond to these requests. Furthermore, the investigation noted that the aircraft was operating during the window of circadian low, a period of natural human fatigue.

Findings

The primary cause was the incorrect judgment by the pilot-in-command when initiating a left turn too early while navigating in low visibility and rain.
The taxiway centerline was barely visible due to the recent painting in March 2017 and the lack of reflective markers near the drain.
There was a lack of coordination between the crew, specifically a failure to respond to the co-pilot's concerns regarding visibility and the need for a "Follow Me" vehicle.
The pilot was operating during a period of high fatigue (circadian low).
The absence of Runway Visual Range (RVR) equipment and the lack of illuminated taxiway centerline lights contributed to the difficulty in navigating the taxiway.