NTSB Factual Report

HISTORY OF FLIGHT

On August 7, 2015, at about 0015 Pacific daylight time, an Embraer ERJ-175LR, N204NN, encountered moderate turbulence near South Lake Tahoe, California, while en route to Reno/Tahoe International Airport (RNO), Reno, Nevada. The two pilots, a forward flight attendant, and 62 passengers were not injured; however, the aft flight attendant sustained serious injuries. The airplane was not damaged. The flight landed at RNO without further incident. The airplane was registered to, and operated by, Compass Airlines as flight 5939 (CPZ5939) under the provisions of 14 Code of Federal Regulations Part 121 as a scheduled commercial flight. Visual meteorological conditions prevailed at the time, and an instrument flight rules flight plan was filed. The flight originated from Los Angeles International Airport (LAX), Los Angeles, California, at 2333.

According to the captain, he advised the cabin crew to finalize the service activities and take their seats for the remainder of the flight. During their subsequent descent, the airplane had two separate encounters with severe turbulence. The forward flight attendant contacted the flight crew, and reported that the aft flight attendant was out of her seat and had injured her ankle. The captain requested the airport medical personnel to wait at the gate, and assess the flight attendant's injury.

The aft flight attendant reported that after the main cabin service was completed and the cart had been stowed, the captain made an announcement to warn the passengers and cabin crew of turbulence. The forward flight attendant had finished collecting service items and approached the aft galley. Both flight attendants continued to secure items because "there was a little rattling, nothing even close to needing to sit down." After the turbulence stopped the aft flight attendant continued to secure drink containers. When the turbulence resumed, the flight attendant was thrown towards the cabin ceiling twice. She hit her head on the emergency exit sign and subsequently fell onto the floor. A few seconds later, the second turbulent jolt threw her back towards the ceiling, and onto the floor at which time two passengers helped her to a jump seat. After several additional minutes of intermittent turbulence the forward flight attendant informed the flight crew that the aft flight attendant was injured. Upon arrival at the gate, the airport medical personnel assessed the injury.

On August 8, 2015, the injured flight attendant informed the company that she had been diagnosed with a right ankle fracture.

METEOROLOGICAL INFORMATION

A NTSB staff meteorologist prepared a report for the area and timeframe surrounding the accident.

The Automated Surface Observation System (ASOS) for Lake Tahoe Airport (TVL), South Lake Tahoe, reported a cloud layer near 14,000 feet near the time of the accident, with lightning detected in the distance within 25 miles northeast of the airport indication of convective echoes and precipitation.

The NWS Reno upper air sounding at 1700 indicated a defined inversion layer between 16,000-17,000 feet with a low-level wind maximum near the top of the inversion of 26 knots. The sounding depicted a conditional stable atmosphere, and indicated a potential of light-to-moderate turbulence at high levels. At 14,000 feet only light turbulence was indicated on the sounding. The level of maximum wind was identified at 44,000 feet with wind from 270 degrees at 93 knots, with the tropopause at 48,000 feet. At 14,000 feet, the wind was from 235 degrees at 12 knots with a temperature of 5 degrees C.

The Geostationary Operational Environmental Satellite (GOES-15) depicted an area of moisture channel darkening occurring immediately west of and bordering the turbulence location associated with downward vertical motion, with a sudden upward motion in the vicinity of the event suggesting convectively induced turbulence potential in the area.

Numerous pilot reports (PIREPs) indicated light to moderate turbulence at various altitudes over the area while one PIREP reported encountering moderate-to-severe-to-extreme turbulence with lightning at 12,000 feet near Las Vegas.

The NWS expected a few scattered rain showers and thunderstorms over the area, below severe limits, and had an AIRMET current for moderate turbulence between 28,000 and 40,000 feet due to the upper level low.

The complete weather formal email is appended to this accident in the public docket.

ADDITIONAL INFORMATION

According to the Federal Aviation Administration (FAA) Northern California Terminal Radar Approach Control Facility (TRACON) summary report, CPZ5939 reported moderate chop at 0017. The TRACON controller advised CPZ5939 to expect moderate chop during its descent to 14,000. CPZ5939 acknowledged and changed the report to moderate turbulence.

At 0018, CPZ5939 reported an encounter with severe turbulence, and asked the controller what information was reflected on radar. The controller responded there was a light precipitation 5 miles ahead of the airplane, and no moderate precipitation.

At 0019, the controller indicated that moderate chop had been reported 15 minutes prior for FL between 200 and 14,000.

At 0020, CPZ5939 reported improved conditions.

The complete summary report is appended to this accident in the public docket.

Flight Attendant Manual (FAM), section 5-35.3 on Turbulence Avoidance states that during moderate or occasional severe and/or severe turbulence, flight attendants are to stop all services and leave carts with brakes engaged until turbulence is reduced and secure themselves in nearest available seat. FAM 5-35.5 is appended to this accident in the public docket.

According to the Compass Airlines Safety Programs manager, pilots' responsibilities during turbulence are solely to notify flight attendants of a turbulent condition ahead of time. After the conditions subside, the flight crew will make a public announcement to inform the flight attendants and passengers.

NTSB Probable Cause

The airplane's encounter with moderate turbulence during descent, which resulted in a serious injury to a flight attendant who was not securely seated. Contributing to the accident was the flight attendant's decision to continue to secure items before the flight crew made an announcement that it was safe to continue with the service activities.