What aircraft was involved and where did it happen?

The accident on 2021-09-04 involved a Interglobe Aviation Ltd., registration VT-IYM, at IN.

What was the probable cause of the accident?

The accident was caused by the aircraft entering turbulent weather and the failure of both the cockpit and cabin crews to adhere to standard operating procedures regarding turbulence preparation and communication.

Cabin Crew Member Injured During Severe Turbulence Encounter

A flight crew's failure to communicate impending turbulence led to a cabin crew member sustaining a fractured leg during a scheduled flight to Bengaluru.

What happened

On 0 September 2021, an ATR 72-212A (600 version), registration VT-IYM, operated by InterGlobe Aviation Ltd, was performing a scheduled flight from Tiruchirapalli to Bengaluru. While cruising at 14,000 feet, the aircraft encountered a period of intense turbulence lasting approximately 26 seconds. During this window, the aircraft experienced significant vertical loads, including a sudden altitude drop of 250 feet.

At the time of the turbulence, a cabin crew member was moving through the cabin to provide service. The sudden movement of the aircraft caused the crew member to fall, resulting in a fractured left leg. The aircraft eventually landed safely in Bengaluru, where medical assistance was provided to the injured crew member.

The investigation

AAIB India's investigation focused on the sequence of events leading to the injury and the crew's adherence to standard operating procedures (SOPs). Investigators examined the flight data recorder (DFDR) and cockpit voice recorder (CVR) to reconstruct the flight path and crew communications.

The inquiry established that the crew had anticipated turbulent weather and had activated the seat belt signs approximately 15 minutes before the encounter. However, the investigation found that the pilot flying (PF) did not verbally notify the pilot monitoring (PM) or the cabin crew that the signs had been activated. Furthermore, the investigation noted that the aircraft's speed was not reduced to the recommended maximum rough air speed (VRA) of 180 knots, as the airspeed reached 207 knots during the event.

Findings

The aircraft encountered dry turbulence that was not detectable by the weather radar due to the lack of water droplets.
A significant communication failure occurred between the cockpit and the cabin; the pilot flying activated the seat belt signs without a verbal call-out or passenger announcement.
The pilot monitoring was preoccupied with paperwork and was unaware that the seat belt signs were illuminated.
The cabin crew did not follow SOPs, as the L2 crew member permitted the L1 crew member to continue service despite the seat belt signs being active.
The primary cause of the injury was the aircraft entering turbulent weather combined with the failure of both cockpit and cabin crews to follow established SOPs regarding seat belt usage and communication.