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B733, en-route, Santa Barbara CA USA, 1999
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| Summary |
|---|
| On 2 September 1999, a United Airlines Boeing Boeing 737-300 in the cruise at FL240, experienced severe turbulence due to an encounter with the wake vortex from a preceding MD11 on a similar track which had climbed through the level of the B737 with minimum lateral separation, 1.5 minutes earlier. |
| Event Details | |
|---|---|
| When | September 1999 |
| Actual or Potential Event Type |
Wake Vortex Turbulence |
| Day/Night | Day |
| Flight Conditions | VMC |
| Flight Details | |
|---|---|
| Aircraft | BOEING 737-300 |
| Operator | United Airlines |
| Domicile | United States |
| Type of Flight | Public Transport (Passenger) |
| Origin | Los Angeles |
| Intended Destination | San Francisco International Airport |
| Take off Commenced | Yes |
| Flight Airborne | Yes |
| Flight Completed | Yes |
| Flight Phase | Cruise |
| ENR | |
| Location En-Route | |
|---|---|
| Origin | Los Angeles |
| Destination | San Francisco International Airport |
| Location | |
|---|---|
| Approx. | near Santa Barbara, CA |
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| |
| WAKE | |
|---|---|
| Tag(s) | ICAO Standard Wake Separation prevailed, In trail event |
| CS | |
|---|---|
| Tag(s) | Turbulence Injury - Cabin Crew Turbulence Injury - Pax with Seat Belts off"Turbulence Injury - Pax with Seat Belts off" is not in the list (Disruptive Pax, Turbulence Injury - Cabin Crew, Cabin Stowage - Pax Items, Toilet compartment fire, Cabin furnishings fire, Evacuation slides deployed, Pax oxygen mask drop, Unauthorised PED use, IFE fire, Cabin air contamination, ...) of allowed values for the "CS" property. |
| Outcome | |
|---|---|
| Damage or injury | Yes |
| Aircraft damage | Minor |
| Injuries | Few occupants |
| Causal Factor Group(s) | |
|---|---|
| Group(s) | Aircraft Operation |
| Safety Recommendation(s) | |
|---|---|
| Group(s) | None Made |
| Investigation Type | |
|---|---|
| Type | Independent |
Description
On 2 September 1999, a United Airlines Boeing Boeing 737-300 in the cruise at FL240, experienced severe turbulence due to an encounter with the wake vortex from a preceding MCDONNELL DOUGLAS MD-11 on a similar track which had climbed through the level of the B737 with minimum lateral separation, 1.5 minutes earlier.
Synopsis
This is an extract from the official report into the accident published by the National Transportation Safety Board (NTSB).
"The flight had just leveled off at FL240 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 nm21,298 m
21.298 km
69,875.328 ft
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."
Related Articles
WAKE
Further Reading
For further information see the NTSB Report (LAX99LA291)