<< >> NASA ASRS Report 1032887, August 2012

A G200 experienced an altitude loss in moderate turbulence at FL410 so after the autopilot pitched up and aircraft speed decreased to maintain FL410; the crew descended to FL370 to maintain stable flight.

Attributes
ACN	1032887
Time
Date	201208
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Gulfstream G200 (IAI 1126 Galaxy)
Operating Under FAR Part	Part 135
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 25 Flight Crew Total 7600 Flight Crew Type 500
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Inflight Event / Encounter Weather / Turbulence

Narrative:

In level flight at FL410 after being in cruise at altitude for approximately 1/2 hour; we experienced some moderate turbulence. Then we felt a buffet and the airspeed started decreasing. The autopilot started pitching the aircraft nose high to maintain altitude. I increased to max take-off power and disconnected the autopilot. We could not maintain altitude and the airspeed was decreasing so we requested descent to FL390. Upon reaching FL390 we continued to feel buffet and requested FL370. We continued the descent to FL370 and the turbulence cleared up. We continued the flight at FL370 for approximately 30 minutes in light turbulence. We requested FL390 for the rest of the flight and did not have any turbulence at FL390.

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Original NASA ASRS Text

Title: A G200 experienced an altitude loss in moderate turbulence at FL410 so after the autopilot pitched up and aircraft speed decreased to maintain FL410; the crew descended to FL370 to maintain stable flight.

Narrative: In level flight at FL410 after being in cruise at altitude for approximately 1/2 hour; we experienced some moderate turbulence. Then we felt a buffet and the airspeed started decreasing. The autopilot started pitching the aircraft nose high to maintain altitude. I increased to max take-off power and disconnected the autopilot. We could not maintain altitude and the airspeed was decreasing so we requested descent to FL390. Upon reaching FL390 we continued to feel buffet and requested FL370. We continued the descent to FL370 and the turbulence cleared up. We continued the flight at FL370 for approximately 30 minutes in light turbulence. We requested FL390 for the rest of the flight and did not have any turbulence at FL390.

Data retrieved from NASA's ASRS site as of July 2013 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.