National Transportation Safety Board
Aviation Accident Final Report

 

 

Location:

Pacific Ocean, United States

Accident Number:

WPR11LA203

Date & Time:

04/11/2011, 0700 UTC

Registration:

N766AN

Aircraft:

BOEING 777-223

Aircraft Damage:

None

Defining Event:

Turbulence encounter

Injuries:

2 Serious, 2 Minor, 227 None

Flight Conducted Under:

Part 121: Air Carrier - Scheduled

Analysis

As the airplane was climbing, the flight crew observed a small weather buildup in front of them. They requested a deviation around the weather, but the air traffic controller requested that they stand by. After entering the weather, they received clearance to turn; however, about 24,000 feet, the airplane encountered about 11 seconds of moderate, and then severe, turbulence. During the encounter, two flight attendants received broken ankles while conducting work in the aft cabin area. The digital flight data recorder revealed that during the encounter vertical acceleration forces went from 2.2G to 0.6913G within 1 second, to a minimum of 0.496G about 5 seconds after the 2.2G maximum.

A weather study conducted by a National Transportation Safety Board meteorologist revealed a frontal wave over the Japanese coast with a warm front extending eastward in the vicinity of the turbulence encounter. A gale force wind was expected. The region of the turbulence encounter also contained low to mid-level clouds with cloud tops near 14,000 feet; cumulonimbus cloud development, with tops up to 26,000 feet, was slightly upstream from the turbulence encounter. Review of the weather package given to the flight crew found no forecasts for turbulence and no Significant Meteorological Information advisories (SIGMETS) were in effect for the route of flight. At the time of the occurrence, there were no reports of turbulence from pilots ahead of the accident flight and the flight crew saw no indication of turbulence on their weather radar.

Probable Cause and Findings

The National Transportation Safety Board determines the probable cause(s) of this accident to be:
An inadvertent encounter with convective-induced turbulence upon entering cumulonimbus clouds.

Findings

Environmental issues

Convective turbulence - Effect on personnel (Cause)

Factual Information

On April 11, 2011, at 6:58:38 coordinated universal time (UTC), American Airlines Flight 170, a Boeing 777-223, N766AN, experienced severe turbulence during climb over international waters about 194 nautical miles east of Narita, Japan. Four flight attendants were injured; two flight attendants sustained minor injuries, while two flight attendants sustained serious injuries. There were no injuries to the other 227 passengers and crew, and the airplane was not damaged. The scheduled international passenger flight originated from Narita International Airport, Narita Japan and was en route to Los Angeles International Airport, Los Angeles, California under the provisions of Title 14 Code of Federal Regulations Part 121. 

The flight crew reported that as the airplane was climbing, they observed a small weather build up in front of them. They requested a deviation around the weather, but ATC informed them to standby. The first officer reported that when the flight crew received the clearance to turn the airplane was already in the weather. At about 24,000 feet, the airplane encountered moderate then severe turbulence for about 11 seconds. Although the seatbelt signs were still illuminated from takeoff, the flight attendants were working in the cabin at the time of the occurrence. 

During the turbulence encounter, both the number 2 and number 3 flight attendants received fractured ankles. The number 2 flight attendant was working in the aft galley when she was thrown to the floor of the airplane, landing hard on her right hand and the outside of her right ankle. The number 3 flight attendant was washing her hands in the 4R lavatory when she could not maintain balance and fell, striking her right foot.

The Digital Flight Data Recorder (DFDR) was sent to the National Transportation Safety Board (NTSB) recorders division for data analysis. According to the DFDR data, the event occurred at 6:58:38; at this time, the airplane was at a pressure altitude of about 24,000 feet, with a speed of 336 KIAS.  During the event, the vertical acceleration went from 2.2G’s to 0.6913G’s within 1 second, to a minimum G of 0.496 about 5 seconds after the 2.2G maximum. 

A weather study conducted by a NTSB meteorologist revealed a frontal wave over the Japanese coast with a warm front extending eastward in the vicinity of the turbulence encountered; developing gale force winds were expected. An upper level chart for 18,000 feet depicted west-southwesterly winds of 40-45 knots in the region. The region also contained low to mid-level clouds with cloud tops near 14,000 feet; cumulonimbus cloud development, with tops up to 26,000 feet, was slightly upstream from the turbulence encounter. At 0732, an airplane along a similar route reported wind at 24,000 feet from 245 degrees at 65 knots. 

Review of the weather package given to the flight crew by American Airlines dispatch found no forecasts for turbulence. No SIGMETS were in effect for the route of flight. At the time of the occurrence, there were no reports of turbulence from airplanes ahead of the accident flight, and the flight crew saw no indications on their weather radar of any returns.

 

History of Flight

Enroute-climb to cruise

Turbulence encounter (Defining event)

 

 

Pilot Information

Certificate:

Airline Transport; Flight Engineer

Age:

61, Male

Airplane Rating(s):

Multi-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:

04/01/2011

Occupational Pilot:

Yes

Last Flight Review or Equivalent:

10/26/2010

Flight Time:

174 hours (Last 90 days, all aircraft), 82 hours (Last 30 days, all aircraft), 0 hours (Last 24 hours, all aircraft)

 

 

Co-Pilot Information

Certificate:

Airline Transport; Flight Engineer

Age:

54, Male

Airplane Rating(s):

Multi-engine Land

Seat Occupied:

Unknown

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:

12/15/2010

Occupational Pilot:

Yes

Last Flight Review or Equivalent:

02/15/2011

Flight Time:

47 hours (Last 90 days, all aircraft), 47 hours (Last 30 days, all aircraft), 0 hours (Last 24 hours, all aircraft)

 

 

Co-Pilot Information

Certificate:

Airline Transport; Flight Engineer

Age:

56, Male

Airplane Rating(s):

Multi-engine Land

Seat Occupied:

Unknown

Other Aircraft Rating(s):

None

Restraint Used:

 

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:

10/19/2010

Occupational Pilot:

Yes

Last Flight Review or Equivalent:

 

Flight Time:

 

 

 

Aircraft and Owner/Operator Information

Aircraft Make:

BOEING

Registration:

N766AN

Model/Series:

777-223

Aircraft Category:

Airplane

Year of Manufacture:

 

Amateur Built:

No

Airworthiness Certificate:

Transport

Serial Number:

32880

Landing Gear Type:

Retractable - Tricycle

Seats:

263

Date/Type of Last Inspection:

 Continuous Airworthiness

Certified Max Gross Wt.:

648000 lbs

Time Since Last Inspection:

 

Engines:

2 Turbo Fan

Airframe Total Time:

33558 Hours at time of accident

Engine Manufacturer:

Rolls Royce

ELT:

Installed, not activated

Engine Model/Series:

Trent 892

Registered Owner:

AMERICAN AIRLINES INC

Rated Power:

 

Operator:

AMERICAN AIRLINES INC

Operating Certificate(s) Held:

Flag carrier (121)

Operator Does Business As:

 

Operator Designator Code:

AALA

 

Meteorological Information and Flight Plan

Conditions at Accident Site:

Visual Conditions

Condition of Light:

Day

Observation Facility, Elevation:

NRT, 141 ft msl

Distance from Accident Site:

194 Nautical Miles

Observation Time:

0630 UTC

Direction from Accident Site:

267°

Lowest Cloud Condition:

Few / 3000 ft agl

Visibility

25 Miles

Lowest Ceiling:

Broken

Visibility (RVR):

 

Wind Speed/Gusts:

65 knots /

Turbulence Type Forecast/Actual:

/

Wind Direction:

245°

Turbulence Severity Forecast/Actual:

/

Altimeter Setting:

 

Temperature/Dew Point:

-38°C

Precipitation and Obscuration:

No Obscuration; No Precipitation

Departure Point:

Narita (NRT)

Type of Flight Plan Filed:

IFR

Destination:

Los Angeles, CA (LAX)

Type of Clearance:

IFR

Departure Time:

0625 UTC

Type of Airspace:

 

 

Airport Information

Airport:

Narita International Airport (NRT)

Runway Surface Type:

 

Airport Elevation:

141 ft

Runway Surface Condition:

 

Runway Used:

N/A

IFR Approach:

None

Runway Length/Width:

 

VFR Approach/Landing:

None

 

Wreckage and Impact Information

Crew Injuries:

2 Serious, 2 Minor, 11 None

Aircraft Damage:

None

Passenger Injuries:

216 None

Aircraft Fire:

None

Ground Injuries:

N/A

Aircraft Explosion:

None

Total Injuries:

2 Serious, 2 Minor, 227 None

Latitude, Longitude:

35.893333, 143.871667 (est)

 


 


Administrative Information

Investigator In Charge (IIC):

Jefferey R Rich

Report Date:

11/29/2011

Additional Participating Persons:

 

Publish Date:

11/29/2011

Investigation Docket:

http://dms.ntsb.gov/pubdms/search/dockList.cfm?mKey=78892