What happened
On 24 October 2017, a Batik Air Boeing 737-800, registration PK-LBY, was performing a scheduled passenger service from Jakarta to Medan, Indonesia. During the descent phase of the flight at approximately 24,500 feet, the aircraft encountered severe turbulence. The intensity of the atmospheric disturbance was significant enough to cause the autopilot to disengage, forcing the crew to fly the aircraft manually for 17 seconds before reengaging the system.
The turbulence lasted roughly 20 seconds, with the Flight Data Recorder capturing vertical accelerations ranging from 2.334 G to -0.482 G. The impact of the turbulence caused several interior components to fail, including the breakage of the aft lavatory ceiling, the displacement of passenger service units, and the dropping of oxygen mask containers.
Following the event, the crew discovered that two occupants had sustained injuries: one flight attendant suffered a fractured leg, and one passenger sustained a serious cervical spine injury. The aircraft continued its descent and landed safely at Kualanamuly International Airport, where medical assistance was requested upon arrival.
The investigation
The KNKT investigation focused on the meteorological conditions and the aircraft's flight path. Investigators confirmed that the aircraft was airworthy and the crew held valid licenses. Meteorological data indicated that the area was prone to developing isolated embedded cumulonimbus clouds, which could reach altitudes above 45,000 feet. The investigation also reviewed the crew's actions, noting that the Second in Command had activated the fasten seat belt sign prior to the most intense period of turbulence. Additionally, the investigators examined the airline's internal response and the communication protocols used during the event.
Findings
- The aircraft encountered severe turbulence while descending through 24,500 feet.
- The vertical acceleration recorded during the event reached a peak of 2.334 G.
- The turbulence caused structural damage to the cabin interior, specifically affecting the aft lavatory and passenger service units.
- One passenger and one flight attendant sustained serious injuries, while another flight attendant sustained minor injuries.
- Weather forecasts had previously indicated the potential for thunderstorms in the destination area.
Safety action
Following the occurrence, Batik Air implemented several safety measures, including issuing a reminder to pilots regarding turbulence anticipation procedures. The airline's Safety Security and Quality Directorate also released a safety circular specifically addressing turbulence encounter anticipation and conducted an internal investigation into communication procedures regarding urgency declarations with air traffic controllers.