Investigation brief · generated 2026-10-09 · source: NTSB public docket and accident database
BOEING 757-222 — Modesto, CA, USA, 2011-12-01
NTSB number
WPR12LA057
Operator
United Airlines
Registration
N547UA
Highest injury
Serious injury
Regulation
Part 121
Damage
—
Cohort
Part 121 airline
Recorder data
Tier 1 — decoded recorder tables
Every sentence below is taken directly from NTSB records — the accident database, the docket's recorder reports and the Board's findings — with its source noted. Nothing is paraphrased or inferred.
NTSB summary
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 flight's encounter with known severe turbulence associated with mountain wave activity, which resulted in a flight attendant sustaining a broken ankle.
Verbatim, NTSB determination.
Flight data recorder
Boeing B757-222 · N547UA — 248,434 samples, 23 parameters, 12:03:00.0 to 14:03:01.0.
Parameter
Max
at
Min
at
Final
at
Pressure altitude ft
36,037.0
13:14:01.8
-188.0
14:01:15.8
-149.0
14:03:00.8
Computed airspeed kts
323.0
13:39:18.7
0.0
12:03:00.7
0.0
14:03:00.7
Vertical acceleration g
1.9
13:39:20.0
0.3
13:39:21.3
1.0
14:03:00.9
Computed from the docket's tabular attachment; times as recorded (local or SRN as published).
Sequence of events (FDR factual report)
Time
Event
Page
1215 PST
Flight departed Denver International Airport (DEN)
1
13:39:16 PST to 13:39:44 PST
Vertical acceleration fluctuated between approximately 0 g's and 2 g's, peaking at a maximum of 1.91 g's and a minimum of 0.25 g's; lateral acceleration fluctuated between about -0.2 g's and 0.2 g's, peaking at a maximum of 0.21 g's and a minimum of -0.17 g's. Autopilot was engaged, pressure altitude was at approximately 30,000 feet, and computed airspeed was about 309 knots.
3
After 13:39:44 PST
Aircraft began its descent from 30,000 feet following the acceleration excursions
3
14:01:01 PST
Aircraft landed
3
Extracted by claude-sonnet-5; 3 of 4 stated events verified against the raw recorder data.