<< >> NASA ASRS Report 397750, March 1998

First officer of an air carrier medium large transport allowed aircraft to descend off cruising altitude by 400 ft due to moderate clear air turbulence. The turbulence caused minor injuries to 2 cabin attendants when they were unexpectedly thrown to the aircraft floor.

Attributes
ACN	397750
Time
Date	199803
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : lax
State Reference	CA
Altitude	msl bound lower : 28600 msl bound upper : 29000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zla
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : flight engineer pilot : commercial
Experience	flight time last 90 days : 240 flight time total : 4600 flight time type : 2000
ASRS Report	397750
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : clearance other anomaly other
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	other
Supplementary
Primary Problem	Weather
Air Traffic Incident	other

Narrative:

We were flying from sfo to san at FL290. A cold front had just passed through the area, but it was now clear and smooth. Approximately 40 NM north of lax we encountered moderate clear air turbulence. This was very strong moderate turbulence. However, we maintained control of the airplane so I would not classify it as severe turbulence. Unfortunately, it was strong enough to throw two of our flight attendants down, both had minor injuries, but were ok. During the encounter we lost 400 ft of altitude. We were in a strong downdraft and I decided it would be better on the airplane to lose the altitude rather than to aggressively try and stay on altitude. ZLA saw the altitude deviation and we reported the turbulence. The wind was blowing out of the west at 117 KTS. Made an uneventful landing at san.

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Original NASA ASRS Text

Title: FO OF AN ACR MLG ALLOWED ACFT TO DSND OFF CRUISING ALT BY 400 FT DUE TO MODERATE CLR AIR TURB. THE TURB CAUSED MINOR INJURIES TO 2 CABIN ATTENDANTS WHEN THEY WERE UNEXPECTEDLY THROWN TO THE ACFT FLOOR.

Narrative: WE WERE FLYING FROM SFO TO SAN AT FL290. A COLD FRONT HAD JUST PASSED THROUGH THE AREA, BUT IT WAS NOW CLR AND SMOOTH. APPROX 40 NM N OF LAX WE ENCOUNTERED MODERATE CLR AIR TURB. THIS WAS VERY STRONG MODERATE TURB. HOWEVER, WE MAINTAINED CTL OF THE AIRPLANE SO I WOULD NOT CLASSIFY IT AS SEVERE TURB. UNFORTUNATELY, IT WAS STRONG ENOUGH TO THROW TWO OF OUR FLT ATTENDANTS DOWN, BOTH HAD MINOR INJURIES, BUT WERE OK. DURING THE ENCOUNTER WE LOST 400 FT OF ALT. WE WERE IN A STRONG DOWNDRAFT AND I DECIDED IT WOULD BE BETTER ON THE AIRPLANE TO LOSE THE ALT RATHER THAN TO AGGRESSIVELY TRY AND STAY ON ALT. ZLA SAW THE ALTDEV AND WE RPTED THE TURB. THE WIND WAS BLOWING OUT OF THE W AT 117 KTS. MADE AN UNEVENTFUL LNDG AT SAN.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.