LJ55 captain reported altitude deviation at FL270 due to either wake vortex or turbulence.

Attributes
ACN	1184462
Time
Date	201407
Local Time Of Day	1201-1800
Place
Locale Reference	ZTL.ARTCC
State Reference	GA
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Learjet 55
Operating Under FAR Part	Part 135
Flight Phase	Descent
Flight Plan	IFR
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument
Experience	Flight Crew Last 90 Days 50 Flight Crew Total 9000 Flight Crew Type 600
Events
Anomaly	Deviation - Altitude Overshoot Deviation - Procedural Clearance Inflight Event / Encounter Wake Vortex Encounter Inflight Event / Encounter Weather / Turbulence

Narrative:

During descent to FL270 we encountered turbulence or aircraft wake turbulence that did not allow the autopilot to level off at the assigned altitude of FL270 and continued to descend about 450 ft below the assigned altitude. I immediately disconnected the autopilot and climbed back to the assigned altitude of FL270. ATC did not inquire; most likely because we were not in rvsm airspace.

Original NASA ASRS Text

Title: LJ55 Captain reported altitude deviation at FL270 due to either wake vortex or turbulence.

Narrative: During descent to FL270 we encountered turbulence or aircraft wake turbulence that did not allow the autopilot to level off at the assigned altitude of FL270 and continued to descend about 450 FT below the assigned altitude. I immediately disconnected the autopilot and climbed back to the assigned altitude of FL270. ATC did not inquire; most likely because we were not in RVSM airspace.

Data retrieved from NASA's ASRS site 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.