<< >> NASA ASRS Report 339267, June 1996

An air carrier B747-400 pilot reports that both he and his captain had to hand fly their aircraft in severe turbulence when the autoplt couldn't handle it. WX factors thunderstorms, severe clear air turbulence.

Attributes
ACN	339267
Time
Date	199606
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : pek
State Reference	FO
Altitude	msl bound lower : 37000 msl bound upper : 37000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zysh
Operator	common carrier : air carrier
Make Model Name	B747-400
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 200 flight time total : 21000 flight time type : 6000
ASRS Report	339267
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	inflight encounter : weather
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : exited adverse environment none taken : anomaly accepted other
Consequence	Other
Supplementary
Primary Problem	Weather
Air Traffic Incident	other

Narrative:

Encountered clear air turbulence causing substantial control difficulty but resulting in no aircraft damage and no personal injuries. Crew observed a small line of thunderstorms across the route, assessing visual and radar data, it was decided to cross said line within the 30 NM space separating the last 2 most westerly tops. In clear smooth air with light quartering headwind of approximately 30 KTS and no reports of turbulence any altitude. Turbulence began abruptly increasing in strength from moderate to heavy and at moments severe, but not choppy, more roller coaster like. It lasted 3-4 mins. The autoplt automatic disengaged and was re-selected a couple of times only to trip off again. Both pilots simultaneously handled the controls and throttles. Targeting an attitude of 4 degree nose up and wings level resulted in optimum stability. It ended as quickly as it started.

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Original NASA ASRS Text

Title: AN ACR B747-400 PLT RPTS THAT BOTH HE AND HIS CAPT HAD TO HAND FLY THEIR ACFT IN SEVERE TURB WHEN THE AUTOPLT COULDN'T HANDLE IT. WX FACTORS TSTMS, SEVERE CLR AIR TURB.

Narrative: ENCOUNTERED CLR AIR TURB CAUSING SUBSTANTIAL CTL DIFFICULTY BUT RESULTING IN NO ACFT DAMAGE AND NO PERSONAL INJURIES. CREW OBSERVED A SMALL LINE OF TSTMS ACROSS THE RTE, ASSESSING VISUAL AND RADAR DATA, IT WAS DECIDED TO CROSS SAID LINE WITHIN THE 30 NM SPACE SEPARATING THE LAST 2 MOST WESTERLY TOPS. IN CLR SMOOTH AIR WITH LIGHT QUARTERING HEADWIND OF APPROX 30 KTS AND NO RPTS OF TURB ANY ALT. TURB BEGAN ABRUPTLY INCREASING IN STRENGTH FROM MODERATE TO HVY AND AT MOMENTS SEVERE, BUT NOT CHOPPY, MORE ROLLER COASTER LIKE. IT LASTED 3-4 MINS. THE AUTOPLT AUTO DISENGAGED AND WAS RE-SELECTED A COUPLE OF TIMES ONLY TO TRIP OFF AGAIN. BOTH PLTS SIMULTANEOUSLY HANDLED THE CTLS AND THROTTLES. TARGETING AN ATTITUDE OF 4 DEG NOSE UP AND WINGS LEVEL RESULTED IN OPTIMUM STABILITY. IT ENDED AS QUICKLY AS IT STARTED.

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.