CHI03LA237

A passenger sustained a broken ankle when the flight encountered moderate turbulence. The captain reported that the seat belt sign was on prior to entering a buildup. The captain stated, "However a passenger, ... had still not taken her seat. Apparently she had been in the lavatory when I turned on the seat belt sign, and was returning to her seat at the time of the encounter." An excerpt from an airline weather study stated, "Even though the main band of convective activity had passed the location of the incident, the possibility of a towering cumulus cell re-building behind the first band was indeed possible as the air mass was becoming gradually unstable again. ... Therefore, the pilot report of encountering a jolt of light turbulence followed by moderate turbulence is plausible."

On July 17, 2003, about 1545 central daylight time a Boeing 777-222, N779UA, operated as United Airlines flight 958 from Denver to Chicago, piloted by an airline transport rated captain and first officer, sustained a serious in-flight injury to one passenger when the flight encountered moderate turbulence near Beloit, Wisconsin. The 14 CFR Part 121 scheduled domestic passenger flight was operating on an IFR flight plan. Visual meteorological conditions prevailed at the time of the accident. The 2 flight crewmembers, 10 cabin crewmembers and the remaining 257 passengers were uninjured. The flight originated from Denver International Airport, Denver, Colorado, about 1300 mountain daylight time and was en route to Chicago O'Hare International Airport (ORD), Chicago, Illinois at the time of the accident. The flight landed at ORD at 1556.

The operator forwarded a copy of the captain's statement. The statement said:

On descent into ORD, approaching from the west, about 2 minutes

after the seat belt sign had been turned on, we penetrated a small

buildup that was difficult to avoid due to other weather and [Air

Traffic Control] constraints. We were painting extensive, very

threatening convective weather to the north and east of the airport,

but the cell we penetrated didn't even show on the radar. We

encountered a jolt of light turbulence, followed by a jolt of moderate

turbulence, total encounter about 5 seconds. My immediate concern

was for my flight attendants since I hadn't had time to warn them.

They were all OK, however a passenger, a woman approximately 70

years old, ... had still not taken her seat. Apparently she had been in

the lavatory when I turned on the seat belt sign, and was returning to

her seat at the time of the encounter. She suffered a badly broken ankle.

United Airlines provided a weather study, which is appended to the docket material associated with this case. An excerpt from that study stated:

Even though the main band of convective activity had passed the

location of the incident, the possibility of a towering cumulus cell

re-building behind the first band was indeed possible as the

airmass was becoming gradually unstable again. The cold front

east-west over southern Wisconsin did not pass the IL/WI border

until 2230UTC. As a result, there was time for cumulus and

towering cumulus to re-develop over the area. Therefore, the

pilot report of encountering a jolt of light turbulence followed by

moderate turbulence is plausible.