Aircraft Accident/Incident Report

Santa Barbara, California 93102
Thursday, September 2, 1999 14:06 PDT

NTSB Narrative Summary Released at Completion of Accident

The flight had just leveled off at flight level 240 with the autopilot still engaged. The seat belt sign had been off for about 5 minutes, and the cabin crew was in the process of preparing a beverage service. The airplane was crossing a VORTAC when the flight encountered turbulence the crew categorized as 'severe,' with a rapid right roll and pitch excursion. The captain disconnected the autopilot and attempted to counter the excursions with control inputs. As a result of the aircraft motions, 1 flight attendant sustained serious injuries, and another flight attendant and 13 passengers sustained minor injuries. The airplane sustained minor damage, limited primarily to ceiling tiles and seats. A review of the meteorological data showed no evidence of any atmospheric phenomena in the area. A simulation study comparing the known airplane response to control inputs versus the motion of the airplane as recorded on the DFDR data showed that the flight controls alone did not cause the recorded motion of the airplane. Radar data established that the flight was in trail of a MD-11 by 11.5 nmi and 97 seconds when the upset occurred. The MD-11 had climbed through the flight's cruise altitude and was 600 feet above the flight at the time of the encounter. Wake vortex studies by NASA have documented vortex descent rates between 270 and 440 feet per minute.

NTSB Probable Cause Narrative

The flight's encounter with wake vortices from a preceding heavy aircraft.

Event Information

Type of Event Accident
Event Date 9/2/1999
Event Day of the Week Thursday
Time of Event 1406
Event Time Zone Pacific Daylight Time
Event City SANTA BARBARA
Event State CALIFORNIA
Event Country --
Zipcode of the event site 93102
Event Date Year 1999
Event Date Month 9
MidAir Collision Indicator No
On Ground Collision occurred ? No
Event Location Latitude --
Event Location Longitude --
Event Location Airport
Event Location Nearest Airport ID
Indicates whether the acc/inc occurred off or on an airport Off Airport/Airstrip
Distance from airport in statute miles --
Degrees magnetic from airport --
Airport Elevation --
Weather Briefing Completeness Full
Investigator's weather source Weather Observation Facility
Time of the weather observation 1353 Pacific Daylight Time
Direction of event from weather observation facility (degrees) 300
Weather Observation Facility ID SBA
Elevation of weather observation facility 10
Distance of event from weather observation facility (units?) 25
Time Zone of the weather observation PDT
Lighting Conditions Day
Lowest Ceiling Height 0
Lowest Non-Ceiling Height 3000
Sky/Lowest/Cloud Conditions Scattered
Sky Condition for Lowest Ceiling None
Visibility Runway Visual Range (Feet) 0
Visibility Runway Visual Value (Statute Miles) 0
Visibility (Statute Miles) 10
Air Temperature at event time (in degrees celsius) 21
Dew Point at event time (in degress fahrenheit) 12
Wind Direction (degrees magnetic) 230
Variable Wind Indicator Unknown
Wind Speed (knots) 9
Wind Velocity Indicator Unknown
Wind Gust Indicator Not Gusting
Wind Gust (knots) 0
Altimeter Setting at event time (in. Hg) 29
Density Altitude (feet) --
Intensity of Precipitation Unknown
METAR weather report --
Event Highest Injury Serious
On Ground, Fatal Injuries 0
On Ground, Minor Injuries 0
On Ground, Serious Injuries 0
Injury Total Fatal --
Injury Total Minor 14
Injury Total None 98
Injury Total Serious 1
Injury Total All 15
Investigating Agency NTSB
NTSB Docket Number (internal use) 1786
NTSB Notification Source --
NTSB Notification Date Sep 2 1999 12:00AM
NTSB Notification Time 1515
Fiche Number and/or location -used to find docket information IMAGE
Date of most recent change to record May 25 2001 4:45AM
User who most recently changed record dbo
Basic weather conditions Visual Meteorological Cond
FAA District Office --

Aircraft Involved

Aircraft #1

Aircraft Registration Number N371UA
NTSB Number LAX99LA291
Missing Aircraft Indicator N
Federal Aviation Reg. Part Part 121: Air Carrier
Type of Flight Plan filed IFR
Flight plan Was Activated? --
Damage Minor
Aircraft Fire None
Aircraft Explosion None
Aircraft Manufacturer's Full Name Boeing
Aircraft Model 737-322
Aircraft Series Identifier 737-322
Aircraft Serial Number 24540
Certified Max Gross Weight 131000
Aircraft Category Airplane
Aircraft Registration Class U.S. Registered/U.S. Soil
Aircraft is a homebuilt? No
Flight Crew Seats --
Cabin Crew Seats --
Passenger Seats --
Total number of seats on the aircraft 141
Number of Engines 2
Fixed gear or retractable gear Retractable
Aircraft, Type of Last Inspection Continuous Airworthiness
Date of Last Inspection Mar 20 1999 12:00AM
Airframe hours since last inspection 1366
Airframe Hours 30420
ELT Installed No
ELT Activated Unknown
ELT Aided Location of Event Site Unknown
ELT Type --
Aircraft Owner Name WILMINGTON TRUST CO
Aircraft Owner Street Address RODNEY SQ NORTH
Aircraft Owner City WILMINGTON
Aircraft Owner State DE
Aircraft Owner Country
Aircraft Owner Zipcode 19890
Operator is an individual? --
Operator Name UNITED AIRLINES, INC.
Operator Same as Owner? No
Operator Is Doing Business As --
Operator Address Same as Owner? No
Operator Street Address P. O. BOX 66100
Operator City CHICAGO
Operator State IL
Operator Country
Operator Zip code 60666
Operator Code UALA
Owner has at least one certificate Yes - certificate holder
Other Operator of large aircraft? No
Certified for Part 133 or 137 Operation Unknown
Operator Certificate Number --
Indicates whether an air carrier operation was scheduled or not Scheduled
Indicates Domestic or International Flight Domestic
Operator carrying Pax/Cargo/Mail Passenger Only
Type of Flying (Per_Bus / Primary) Unknown
Second Pilot on Board Yes
Departure Point Same as Event No
Departure Airport Code LAX
Departure City LOS ANGELES
Departure State CA
Departure Country
Departure Time 1326
Departure Time Zone PDT
Destination Same as Local Flt --
Destination Airport Code SFO
Destination City SAN FRANCISCO
Destination State CA
Destination Country
Specific Phase of Flight --
Report sent to ICAO? --
Evacuation occurred --
Date of most recent change to record May 25 2001 4:09AM
User who most recently changed record dbo
Since inspection or accident --
Event Location Runway Number and Location 0
Runway Length --
Runway Width --
Sight Seeing flight No
Air Medical Flight No
Medical Flight --