National Transportation Safety Board
Aviation Accident Final Report

 

 

Location:

Laverne, OK

Accident Number:

WPR12LA144

Date & Time:

03/20/2012, 0830 CDT

Registration:

N247WN

Aircraft:

BOEING 737-7H4

Aircraft Damage:

None

Defining Event:

Turbulence encounter

Injuries:

1 Serious, 141 None

Flight Conducted Under:

Part 121: Air Carrier - Scheduled

Analysis

The flight had been experiencing moderate turbulence along its route. Once the turbulence had subsided, the seatbelt sign was turned off. The flight attendants had resumed their service when the flight encountered three additional turbulence jolts. The aft galley flight attendant was trying to get seated and strapped into the jumpseat but was injured when another turbulence jolt occurred. She was thrown across the galley and hit her back/ribs on an object. Flight data recorder information showed that vertical accelerations fluctuated between about 0.75 g and 1.2 g; lateral accelerations also fluctuated during this period, between about +/- 0.05 g. An airmen’s meteorological information  advisory for moderate turbulence was active for the accident location at the time. A significant meteorological information advisory for occasional severe turbulence was active for an area west of the accident location.

Probable Cause and Findings

The National Transportation Safety Board determines the probable cause(s) of this accident to be:
The airplane’s encounter with severe turbulence during cruise flight, which resulted in a serious injury to a flight attendant.

Findings

Environmental issues

Clear air turbulence - Effect on personnel (Cause)

Factual Information

HISTORY OF THE FLIGHT

On March 20, 2012, at 0830 central daylight time, a Boeing 737-7H4, N247WN, experienced turbulence during cruise flight near Laverne, Oklahoma. Southwest Airlines operated the airplane as Flight 162 under the provisions of 14 Code of Federal Regulations Part 121. The flight crew, 2 flight attendants, and 137 passengers were not injured; 1 flight attendant sustained serious injuries. The airplane was not damaged. An instrument flight rules (IFR) flight plan had been filed for the flight that departed Tampa International Airport (TPA), Tampa, Florida, at 0653 eastern daylight time. The flight was destined for Phoenix Sky Harbor International Airport (PHX), Phoenix, Arizona.

According to Southwest Airlines, the airplane was in cruise flight over Laverne when it encountered three turbulence jolts. The aft galley flight attendant was injured while trying to get seated and strapped into the jump seat when another turbulence jolt occurred. The flight attendant was able to perform all required safety duties for the remainder of the flight, but reported significant back pain upon arrival to Phoenix. The flight attendant was not transported to a hospital. On March 22, the flight attendant informed the company that she had been diagnosed with a rib fracture.

In statements submitted by the flight attendants, they reported that there was a long duration of turbulence during cruise. When the turbulence diminished, the seatbelt sign was turned off. They got up and then it started to become turbulent again. As the two flight attendants in the back of the airplane attempted to secure themselves in the aft jumpseats, one of them was thrown across the galley and hit her back/ribs on an object.

FLIGHT RECORDERS

Data obtained from the flight data recorder (FDR) showed that the airplane climbed to flight level 380 shortly after departure. About 0824, winds aloft speed calculated by the flight management computer (FMC) was about 140 knots from about 160 degrees true. For about 5 minutes around this time at flight level 380, vertical accelerations fluctuated between about 0.75g and 1.2g; lateral accelerations also fluctuated during this period, between about +/- 0.05g. At 0827, the airplane descended from flight 380 to flight level 340. Shortly after the descent began, the fluctuations in vertical and lateral accelerations decreased, fluctuating between 0.997g and 1.004g and +/- 0.01g, respectively. After 9 minutes at flight level 340, during the period of otherwise decreased vertical and lateral accelerations, the vertical acceleration varied from about 0.255g to 1.7g within a 1-second period of time at 08:38:20. About 20 minutes after this vertical acceleration encounter, the FMC calculated a decrease in winds aloft at flight level 320 to under 30 knots for about 12 minutes; during this 12-minute period the winds aloft shifted from about 160 degrees true to 340 degrees true. 

Because this was not determined to be an accident until 2 days after the event, the cockpit voice recorder information was written over by normal use.

METEOROLOGICAL INFORMATION

A Senior Meteorologist completed a weather study. A 250-hectopascal (hPa) analysis chart obtained from the Storm Prediction Center and valid for 0700 central daylight time (CDT) identified a portion of a jet stream stretching north from central Texas into Canada. A jet streak (localized regions of very fast winds embedded within the jet stream) was identified in the vicinity of the accident location with southerly wind magnitudes greater than 150 knots. Calculations by the Rawinsonde Observation Program (RAOB) indicated the potential for significant clear-air turbulence between about 36,000 and 40,000 feet.

An Airmen’s Meteorological Information (AIRMET) advisory for moderate turbulence between FL220 and FL430 was issued at 0525 CDT and was active for the accident location at the accident time. A Significant Meteorological Information (SIGMET) advisory for occasional severe turbulence between FL330 and FL380 was issued at 0526 CDT for an area west of the accident location. This SIGMET was valid until 0926 CDT.

 

History of Flight

Enroute-cruise

Turbulence encounter (Defining event)

 

 

Pilot Information

Certificate:

Airline Transport; Flight Instructor

Age:

47, Male

Airplane Rating(s):

Multi-engine Land; Single-engine Land

Seat Occupied:

Left

Other Aircraft Rating(s):

None

Restraint Used:

Seatbelt, Shoulder harness

Instrument Rating(s):

Airplane

Second Pilot Present:

Yes

Instructor Rating(s):

Airplane Multi-engine; Airplane Single-engine; Instrument Airplane

Toxicology Performed:

No

Medical Certification:

Class 1 Without Waivers/Limitations

Last FAA Medical Exam:

03/14/2012

Occupational Pilot:

Yes

Last Flight Review or Equivalent:

02/03/2012

Flight Time:

23050 hours (Total, all aircraft), 18050 hours (Total, this make and model), 17350 hours (Pilot In Command, all aircraft), 189 hours (Last 90 days, all aircraft), 83 hours (Last 30 days, all aircraft), 6 hours (Last 24 hours, all aircraft)

 

 

Co-Pilot Information

Certificate:

Airline Transport

Age:

42, Male

Airplane Rating(s):

Multi-engine Land; Single-engine Land

Seat Occupied:

Right

Other Aircraft Rating(s):

None

Restraint Used:

Seatbelt, Shoulder harness

Instrument Rating(s):

Airplane

Second Pilot Present:

Yes

Instructor Rating(s):

None

Toxicology Performed:

No

Medical Certification:

Class 1 Without Waivers/Limitations

Last FAA Medical Exam:

10/18/2011

Occupational Pilot:

Yes

Last Flight Review or Equivalent:

09/09/2011

Flight Time:

7997 hours (Total, all aircraft), 3622 hours (Total, this make and model), 2810 hours (Pilot In Command, all aircraft), 143 hours (Last 90 days, all aircraft), 19 hours (Last 30 days, all aircraft), 5 hours (Last 24 hours, all aircraft)

 

 

Aircraft and Owner/Operator Information

Aircraft Make:

BOEING

Registration:

N247WN

Model/Series:

737-7H4

Aircraft Category:

Airplane

Year of Manufacture:

 

Amateur Built:

No

Airworthiness Certificate:

Transport

Serial Number:

32508

Landing Gear Type:

Retractable - Tricycle

Seats:

140

Date/Type of Last Inspection:

03/15/2012, Continuous Airworthiness

Certified Max Gross Wt.:

154500 lbs

Time Since Last Inspection:

103 Hours

Engines:

2 Turbo Fan

Airframe Total Time:

20917 Hours as of last inspection

Engine Manufacturer:

CFM INTL

ELT:

Not installed

Engine Model/Series:

CFM56-7B24

Registered Owner:

SOUTHWEST AIRLINES CO

Rated Power:

24200 lbs

Operator:

SOUTHWEST AIRLINES CO

Operating Certificate(s) Held:

Flag carrier (121)

Operator Does Business As:

 

Operator Designator Code:

SWAA

 

Meteorological Information and Flight Plan

Conditions at Accident Site:

Visual Conditions

Condition of Light:

Day

Observation Facility, Elevation:

WWR, 2189 ft msl

Distance from Accident Site:

26 Nautical Miles

Observation Time:

0835 CDT

Direction from Accident Site:

315°

Lowest Cloud Condition:

Clear

Visibility

10 Miles

Lowest Ceiling:

None

Visibility (RVR):

 

Wind Speed/Gusts:

7 knots /

Turbulence Type Forecast/Actual:

/

Wind Direction:

140°

Turbulence Severity Forecast/Actual:

/

Altimeter Setting:

29.73 inches Hg

Temperature/Dew Point:

8°C / 6°C

Precipitation and Obscuration:

No Obscuration; No Precipitation

Departure Point:

Tampa, FL (TPA)

Type of Flight Plan Filed:

IFR

Destination:

Phoenix, AZ (PHX)

Type of Clearance:

IFR

Departure Time:

0653 EDT

Type of Airspace:

 

 

Airport Information

Airport:

West Woodward Airport (WWR)

Runway Surface Type:

 

Airport Elevation:

2189 ft

Runway Surface Condition:

 

Runway Used:

N/A

IFR Approach:

None

Runway Length/Width:

 

VFR Approach/Landing:

None

 

Wreckage and Impact Information

Crew Injuries:

1 Serious, 4 None

Aircraft Damage:

None

Passenger Injuries:

137 None

Aircraft Fire:

None

Ground Injuries:

N/A

Aircraft Explosion:

None

Total Injuries:

1 Serious, 141 None

Latitude, Longitude:

36.551667, -0.619444 (est)

 


 


Administrative Information

Investigator In Charge (IIC):

Tealeye Cornejo

Report Date:

10/29/2013

Additional Participating Persons:

Tod E Jacobs; Federal Aviation Administration - CMO; Phoenix, AZ

Dennis Post; Southwest Airlines; Dallas, TX

Publish Date:

10/29/2013

Investigation Docket:

http://dms.ntsb.gov/pubdms/search/dockList.cfm?mKey=83196