What happened
On February 10, 2024, at approximately 15:43 EST, a Boeing 777-222ER, registration N788UA, was descending through FL210 toward Newark Liberty International Airport (EWR) when it encountered moderate-to-severe turbulence. The aircraft was operating as a scheduled domestic flight from Los Angeles (LAX) under instrument meteorological conditions (IMC).
Prior to the encounter, the flight crew had monitored weather applications and received no significant turbulence warnings. While the crew was descending, the captain instructed the cabin crew to prepare for landing and activated the seatbelt sign. During the descent, the aircraft passed through a region of intense vertical acceleration, with recorded fluctuations between -0.55 g and +1.82 g.
As a result of the sudden movement, several crewmembers were lifted from their positions and struck the cabin ceiling. Three flight attendants sustained serious injuries: one suffered a shattered femur and spinal compression fractures, another sustained an intracranial bleed, and a third suffered a head laceration. At least one passenger was also reported to have struck the ceiling.
The investigation
Investigators analyzed Quick Access Recorder (QAR) data, which confirmed rapid vertical acceleration during the event. Meteorological analysis revealed the aircraft was flying near a cold front and a strong jet stream of 1t50 knots. The presence of transverse banding in satellite imagery and high eddy dissipation rate (EDR) values indicated the aircraft encountered convective updrafts and wind shear at the tops of rain showers.
An investigation of Air Traffic Control (ATC) communications revealed that an uninvolved aircraft, ACA548, had reported moderate turbulence to the controller approximately three minutes before the N788UA encounter. However, the controller did not disseminate this Pilot Weather Report (PIREP) to the United Airlines flight. Additionally, while an ACARS message containing a turbulence warning was sent to the aircraft, it could not be determined if the crew had read it before the encounter.