N788UA – BOEING 777-222ER – 2024-02-10 NTSB Accident Report

HISTORY OF FLIGHTOn February 10, 2024, about 15:43 EST, UAL1890, a Boeing 777-222ER, N788UA, encountered moderate to severe turbulence while descending to FL190 inbound to EWR. Of the 280 passengers and crewmembers on board, three flight attendants sustained serious injuries. The flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 121 as a scheduled domestic passenger flight from LAX to EWR.

Both flight crewmembers reported being well-rested before the flight and stated that they conducted a thorough preflight briefing, which included a review of forecasted turbulence near the EWR terminal area. The first officer (FO) used the WSI and SkyPath electronic flight bag (EFB) applications to assess turbulence reports, noting light to moderate activity near the usual WILLIAMSPORT3 arrival. Based on this, the crew anticipated and accepted a northerly routing via the FLOSI4 arrival for turbulence avoidance.

According to Automatic Dependent Surveillance–Broadcast (ADS-B) data, flight UAL1890 departed LAX at approximately 0831 Pacific Standard Time (PST). The FO was the pilot flying (PF) and the captain was the pilot monitoring (PM). The flight crew stated that the departure from LAX was uneventful, and the airplane leveled off at a cruise altitude of FL350.

About 1334 EST, the flight crew sent a message via Aircraft Crew Alerting and Reporting System (ACARS) to their dispatcher, stating that they were having a “smooth ride past hour or so, how’s descent into EWR.” About one minute later, the dispatcher replied, “so far only complaint is a moderate by a regional jet.” The flight subsequently climbed to its cruise altitude of FL370. There was no additional communication between the flight and the dispatcher until after the encounter with turbulence. The seatbelt sign was cycled ON and OFF in accordance with standard turbulence mitigation procedures, including passenger address (PA) announcements. The WSI and Skypath applications were continuously monitored, and no significant turbulence was indicated along the route or during the approach phase.

The FO stated that he was responsible for briefing the approach/arrival into EWR and in preparation for the brief, checked for potential turbulence using the WSI and SkyPath application to see if there were any reports of turbulence. Neither application revealed any significant indications of turbulence along their route. After the brief, the captain turned the onboard weather radar ON for the eventual descent into EWR.

As the airplane began its descent into EWR, ATC issued step-down clearances. About 1437, the flight began a descent to FL350 where it remained for about 20 minutes. The flight then turned towards an easterly direction and began a descent to FL330. About 1510, the flight began to descend to FL310.

At 1532:30, the crew of ACA548 (an uninvolved airplane) checked in with the R24A controller and was provided with a pilot weather report (PIREP) indicating moderate to heavy precipitation near the Hancock VOR (HNK), with light to moderate chop, in the descent from FL220 to FL190.

At 1535:10, the flight crew of UAL1890 checked in with the R24A controller and indicated that they were level at FL270. The R24A controller did not respond. In a postaccident interview, the R24A controller stated they did not respond at the time because they were completing other coordination. According to the flight crew, while passing through FL270, the captain announced via the PA that the flight attendants prepare the cabin for landing, followed by turning the seatbelt sign ON.

At 1536:00, the R24A controller instructed the flight to descend to FL240.

At 1538:14, the R24A controller conducted a position relief briefing with the R24C controller.

At 1540:38, the R24C controller instructed the crew of ACA548 to contact the Stewart sector (R05) controller. The crew of ACA548 acknowledged the frequency change and advised the R24C controller they had encountered moderate turbulence. The controller did not acknowledge or disseminate this PIREP to other aircraft, including UAL1890, as required by FAA procedures for Pilot Weather Report (PIREPs) solicitation and dissemination. In a postaccident interview, the controller stated they did not hear the PIREP.

At 1540:52, the R24C controller instructed UAL1890 to cross five miles past the HNK VOR at FL190. The crew acknowledged the instructions. The FO stated that he observed an overcast layer of clouds ahead and below that the flight would penetrate during descent. The flight crew stated there was no indication of potential turbulence as nothing showed on the airplane's weather radar or the SkyPath app. Additionally, there were no reports of turbulence provided by ATC or dispatch directly to the flight crew.

At 1541, a turbulence pilot report (PIREP) was sent to the flight via ACARS stating “YOUR FLIGHT IS IN CLOSE PROXIMITY TO A MOD TURB PIREP EVENT REPORTED BY A B789 AT 2022 (1522 local) Z FL220 LOCATION HNK RMK TB MOD CHOP 220-190 YOU CLOSEST POINT TO EVENT AT 2041Z”.  It could not be conclusively determined if the crew saw or read the message.

At 1542:18, the crew of UAL1890 asked the R24C controller to confirm they were instructed to cross five miles past the HNK VOR and the controller responded in the affirmative.

At 1543:06, the R24C controller instructed the crew of UAL1890 to contact the R05 controller. The crew acknowledged the frequency change and advised the R24C controller they had encountered “severely moderate turbulence.” The controller did not respond.

At 1544:07, the crew of UAL1890 checked in with the R05 controller and reported descending to FL190. The R05 controller acknowledged and advised the crew of precipitation and light to moderate turbulence along their route of flight. The crew responded and stated that they had encountered moderate turbulence when they were at FL210.

The flight crew reported that while descending through about FL210 in IMC, the airplane encountered moderate turbulence lasting a few seconds that caused unsecured items on the flightdeck to be thrown about. A visual break in the clouds was observed, and the crew initiated a right turn using heading select mode to exit the turbulent layer.

Following the event, the captain immediately called the cabin crew and was informed of multiple injuries with one flight attendant sustaining a head laceration. The flight crew declared a medical emergency and requested paramedics meet the airplane at the gate.

The remainder of the approach, landing, and taxi were uneventful. Upon arrival at the gate, passengers were instructed to remain seated to allow emergency medical services (EMS) personnel to board. Port Authority Police and EMS responded and attended to the injured flight attendants. Three aft-galley flight attendants (FA 2, FA3, FA 9) were transported to the hospital by ambulance. The captain and FO assisted in managing the cabin and supporting the crew and passengers during deplaning. Additional crewmembers later sought medical evaluation for head, neck, back, and extremity pain. Post-flight, two FAs were diagnosed with fracture injuries and a third was diagnosed with a sub-cranial bleed. AIRCRAFT INFORMATIONThe airplane was a Boeing 777-222ER, manufacturing Serial Number 26942. The airplane was manufactured in 1997, delivered to United Airlines in July of 1997 and it held a transport category airworthiness certificate. The airplane was configured with 4 flight crew seats, 14 flight attendant seats, and 276 passenger seats.

Figure 4: Accident Airplane, N788UA (Courtesy of planespotters.net)

At the time of the event, the airplane had two deferrals from the minimum equipment list (MEL). Those deferrals were for the broadband antenna and the autoland system. METEOROLOGICAL INFORMATIONThe National Weather Service (NWS) Surface Analysis Chart, centered over the northeastern United States for 1600 EST, depicted the accident site was located east of a frontal boundary.

The Constant Pressure Charts for 1900 EST indicated a mid-level trough over the Great Lakes region. These charts are updated every 6 hours and the 1900 EST time is the closest to the accident time. Troughs and fronts can act as lifting mechanisms to help produce clouds and precipitation when sufficient moisture is present. The 700-hPa constant pressure chart showed westerly wind around 40 knots, becoming a southwest 50 knot wind by 500-hPa, and about 30,000 ft identified the jet stream maximum, which stretched from Michigan eastward into New York, with winds of 150 knots and was located in the vicinity of the accident site.

The accident occurred in an area where a chance of general thunderstorms had been predicted.

Observations from the BGM Automated Surface Observing System (ASOS), around the accident time, identified marginal visual flight rules (MVFR) to visual flight rules (VFR) conditions around the accident time with IFR conditions due to visibility restrictions when the thunderstorm activity went across BGM between 1353 and 1453 EST. During the period from 1423 through 1453, BGM reported lightning activity associated with the thunderstorms. In addition, winds gusted as high as 31 knots.

An HRRR model sounding was created for the approximate accident site coordinates for 1600 EST. The sounding indicated a conditionally unstable atmosphere from the surface through 4,000 ft, transitioning to a stable atmosphere above 4,000 ft. Convective Available Potential Energy (CAPE) was 16 Joules/kilogram (J/kg), with the maximum vertical velocity (MVV) for this atmosphere calculated as 6 meters/second (about 1,181 ft per minute). Rawinsonde Observation (RAOB) indicated cloud cover in two layers between 3,000 ft and 18,000 ft with another cloud layer near 25,000 ft. RAOB also indicated moderate rime and mixed icing between 6,500 ft and 15,000 ft.

Based on the 1600 EST HRRR sounding, wind speed increased to 40 knots by 10,000 ft and t...