Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 50; Flight Crew Total 9000; Flight Crew Type 600
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Wake Vortex Encounter; Inflight Event / Encounter Weather / Turbulence
Flight Crew Returned To Clearance
Environment - Non Weather Related; Weather
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.
LJ55 Captain reported altitude deviation at FL270 due to either wake vortex or turbulence.