Boeing 757-222 accident near Modesto, California, December 1, 2011
On December 1, 2011 at about 9:39 pm local time, a Boeing 757-222, registered N547UA, was involved in an accident during approach (IFR initial approach) near Modesto, California. It was flown under scheduled airline rules (Part 121). 1 person was seriously injured; 151 others were unhurt. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
The flight's encounter with known severe turbulence associated with mountain wave activity, which resulted in a flight attendant sustaining a broken ankle.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- December 1, 2011 · about 9:39 pm local time
- Place
- Modesto, California · map
- Type
- Accident
- Injuries
- 1 person was seriously injured; 151 others were unhurt.
- Weather
- visual conditions (good weather)
- Aircraft
- Boeing 757-222 · all 757-222s on the register
- Registration
- N547UA · no longer on the register · serial 25368
- Damage
- Not recorded
- Flight
- Flight · scheduled airline rules (Part 121)
The NTSB's narrative final · quoted from the NTSB record
While en route at flight level (FL) 360, the captain of the commercial air carrier flight requested and was granted a lower altitude (FL 300) to minimize the effect that turbulence was having on the airplane. After the captain received pilot reports indicating that varying degrees of turbulence, mountain wave activity, and low-level windshear existed, he illuminated the seat belt sign and made an announcement for the passengers to be seated. The flight crew then advised the cabin crewmembers of possible turbulence and instructed them to prepare the cabin for landing, stay near their seats, and be seated immediately if turbulence was encountered. About 7 to 10 minutes later, while the airplane was at FL 300, the flight encountered moderate-to-severe turbulence. A flight attendant who was in the lavatory when the turbulence was encountered sustained a broken ankle after being thrown in the air twice.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
What happened, in order
- Turbulence encounter during approach (IFR initial approach) defining event
The NTSB's findings
- cause Environmental issues › Conditions/weather/phenomena › Turbulence › Terrain induced turbulence › Effect on equipment
Pilot
- Certificate: airline transport pilot
- Ratings: multi-engine land; instrument: airplane
- Flight time: 11,290 hours in all; 3,823 in this make and model
- Last flight review: September 1, 2011
- Medical certificate: Class 1 (with waivers/limitations)
- Seat: left
- Injury: no injuries
Co-pilot
- Certificate: airline transport pilot
- Ratings: multi-engine land; instrument: airplane
- Flight time: 9,469 hours in all; 6,782 in this make and model
- Medical certificate: Class 2
- Seat: rgt
- Injury: no injuries
The aircraft
- Airframe total time: 74,780 hours
- Last inspection: continuous airworthiness programme, December 1, 2011
- Seats: 178
- Landing gear: fixed
- Engine 1: P & W PW2040 (turbojet); 0 hours total
- Engine 2: P & W PW2040 (turbojet); 0 hours total
- Operator: United Airlines
The flight
- Departed from: DEN Denver CO at 6:15 pm
- Destination: SFO San Francisco CA
- Flight plan: IFR
- A second pilot was aboard
Weather at the time
- Light: daylight
- Wind: from 340° at 24 knots, gusting 29
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 66°F (19°C), dew point 19°F (-7°C)
- Altimeter: 30.02 inHg
- Observation at 8:53 pm from MOD, 62 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Cabi | 1 | 3 | ||
| Flight crew | 2 | |||
| Passengers | 146 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
The docket, the folder of records gathered during an investigation (maintenance records, photographs, witness statements, examinations), has not been read from the NTSB for this case yet; the list appears here once it has. Open the docket at the NTSB.
Everything on this page comes from the NTSB's public records. The narrative, probable cause and findings are the NTSB's own words; the coded tables behind the report are written out in plain English, with pilots' ages, home towns and medical details left out. The documents and photographs are the NTSB's docket, shown as the NTSB released them. This site's own text never names anyone involved. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.