National Transportation Safety Board
Aviation Accident Final Report

 

 

Location:

Pawnee, NE

Accident Number:

WPR12LA119

Date & Time:

02/23/2012, 1430 CST

Registration:

N915WN

Aircraft:

BOEING 737-7H4

Aircraft Damage:

None

Defining Event:

Turbulence encounter

Injuries:

1 Serious, 1 Minor, 138 None

Flight Conducted Under:

Part 121: Air Carrier - Scheduled

Analysis

The airplane had been cruising in smooth air conditions for over 30 minutes when it suddenly encountered 2 to 3 seconds of moderate turbulence. The momentary altitude and roll deviation of the airplane, which was corrected by the autopilot, threw one of the flight attendants against the airplane structure, which resulted in a serious injury to her hand. The flight crew had not been given any turbulence advisories by air route traffic controllers, and the flight crew had not overheard any airplanes in the area reporting moderate turbulence. Immediately after the encounter, the airplane continued in smooth air conditions.

Probable Cause and Findings

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

Findings

Personnel issues

Illness/injury - Cabin crew

Environmental issues

Clear air turbulence - Effect on operation (Cause)

Factual Information

On February 23, 2012, about 1430 central standard time, a Southwest Airlines Boeing 737-7H4, N915WN, encountered 2 to 3 seconds of moderate turbulence while in cruise flight between Chicago, Illinois, and Los Angles, California. The Captain and the First Officer, both of whom were airline transport pilots, were not injured, nor were any of the 135 passengers. One of the three flight attendants received minor injuries, and a second flight attendant received a serious injury to her right hand. The airplane was not damaged. The 14 Code of Federal Regulations Part 121 scheduled domestic passenger flight, which departed Chicago Midway Airport about 55 minutes prior to the turbulence encounter, was en route to Los Angeles International Airport, Los Angeles, California. At the time of the event, the airplane was in visual meteorological conditions on an Instrument Flight Rules flight plan.

According to the flight crew, they were in level cruise flight in smooth air at Flight Level 360, when the airplane experienced the turbulence encounter. Although the airplane had encountered periods of light chop earlier in the flight, it had been in completely smooth air for about 30 minutes prior to the event, and there had been no report of turbulence from the Air Route Traffic Control Center, nor had the flight crew overheard any other aircrew stating that there was anything but smooth air in the area of the encounter. Although the flight attendants were in the process of serving drinks, the passenger seatbelt sign was still on from the earlier period of choppy air. At the moment of the encounter, the airplane experienced both a momentary altitude deviation and a left roll of less than 10 degrees, both of which were corrected by the autopilot, with a slight overshoot past the wings level position. During the encounter sequence, one flight attendant was thrown back against the aft galley door, whereupon her hand hit the recyclable can door. She then immediately felt pain in the hand. At that point in time, the Captain came on the public address system and directed the flight attendants to take their seats immediately, which they did until the flight crew was convinced that they had returned to smooth air conditions. Although the injured flight attendant continued her in-flight duties until the plane landed in Los Angeles, she ultimately went to Urgent Care for treatment. X-rays taken of her hand determined that she had a closed fracture of the carpal bone in her right hand.

According to both flight crew members, the airplane reacted in a manner consistent with it flying through the wake of another preceding or crossing airplane, and after the few seconds of the turbulence encounter, followed by the correction by the autopilot, the airplane returned to straight and level flight in smooth air.

 

History of Flight

Enroute-cruise

Turbulence encounter (Defining event)

 

 

Pilot Information

Certificate:

Airline Transport

Age:

52, 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):

None

Toxicology Performed:

No

Medical Certification:

Class 1 With Waivers/Limitations

Last FAA Medical Exam:

02/07/2012

Occupational Pilot:

Yes

Last Flight Review or Equivalent:

11/02/2011

Flight Time:

23500 hours (Total, all aircraft), 20550 hours (Total, this make and model), 16000 hours (Pilot In Command, all aircraft), 200 hours (Last 90 days, all aircraft), 75 hours (Last 30 days, all aircraft), 7 hours (Last 24 hours, all aircraft)

 

 

Co-Pilot Information

Certificate:

Airline Transport

Age:

44, 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:

07/18/2011

Occupational Pilot:

Yes

Last Flight Review or Equivalent:

09/17/2011

Flight Time:

9887 hours (Total, all aircraft), 6010 hours (Total, this make and model), 1977 hours (Pilot In Command, all aircraft), 208 hours (Last 90 days, all aircraft), 75 hours (Last 30 days, all aircraft), 3 hours (Last 24 hours, all aircraft)

 

 

Aircraft and Owner/Operator Information

Aircraft Make:

BOEING

Registration:

N915WN

Model/Series:

737-7H4

Aircraft Category:

Airplane

Year of Manufacture:

 

Amateur Built:

No

Airworthiness Certificate:

Transport

Serial Number:

36888

Landing Gear Type:

 

Seats:

145

Date/Type of Last Inspection:

02/09/2012, Continuous Airworthiness

Certified Max Gross Wt.:

154500 lbs

Time Since Last Inspection:

 

Engines:

2 Turbo Fan

Airframe Total Time:

14201 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:

SWA

 

Meteorological Information and Flight Plan

Conditions at Accident Site:

Visual Conditions

Condition of Light:

Day

Observation Facility, Elevation:

 

Distance from Accident Site:

 

Observation Time:

 

Direction from Accident Site:

 

Lowest Cloud Condition:

Scattered / 2700 ft agl

Visibility

10 Miles

Lowest Ceiling:

Overcast / 3200 ft agl

Visibility (RVR):

 

Wind Speed/Gusts:

19 knots / 25 knots

Turbulence Type Forecast/Actual:

/

Wind Direction:

300°

Turbulence Severity Forecast/Actual:

/

Altimeter Setting:

29.43 inches Hg

Temperature/Dew Point:

8°C

Precipitation and Obscuration:

No Obscuration; No Precipitation

Departure Point:

Chicago, IL (KMDW)

Type of Flight Plan Filed:

IFR

Destination:

Las Angeles, CA (KLAX)

Type of Clearance:

IFR

Departure Time:

1335 CST

Type of Airspace:

 

 

 

Wreckage and Impact Information

Crew Injuries:

1 Serious, 1 Minor, 3 None

Aircraft Damage:

None

Passenger Injuries:

135 None

Aircraft Fire:

None

Ground Injuries:

N/A

Aircraft Explosion:

None

Total Injuries:

1 Serious, 1 Minor, 138 None

Latitude, Longitude:

40.168889, -96.151944 (est)

 


 


Administrative Information

Investigator In Charge (IIC):

Orrin K Anderson

Report Date:

01/31/2013

Additional Participating Persons:

Owen Grimm; Lincoln FSDO; Lincoln, NE

Dennis Post; Southwest Airlines; Dallas, TX

Publish Date:

01/31/2013

Investigation Docket:

http://dms.ntsb.gov/pubdms/search/dockList.cfm?mKey=82993