BAe 125 Series 800
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 20; Flight Crew Total 11876; Flight Crew Type 35
Inflight Event / Encounter Other / Unknown
Flight Crew Diverted; General Declared Emergency
Weather; Aircraft
Cruising in occasional light chop at FL400 at Mach .74 = 220 KIAS. The airframe started to vibrate at a rate similar to moderate to severe chop. We thought we had an airframe flutter or automated flight control system malfunction. We requested a lower altitude and were cleared to FL350. In the descent we declared an emergency. The Captain used the autopilot to descend and level off at FL350 where he turned off the autopilot. The aircraft stopped vibrating. The Captain flew the rest of the flight by hand. We asked Center for a clearance to a nearby airport. They cleared us to the airport. In the descent we experienced some turbulence; but no more airframe vibration. We told Center fuel and souls on board; and that the aircraft was under control and we no longer considered it to be an emergency. We landed uneventfully. The passengers said the wing tips fluctuated up and down about 3 FT at a rate of about 3 oscillations per second. This lasted for about 3 to 4 minutes.
During a callback conversation the reporter stated Maintenance had determined there was a service bulletin regarding reported vibrations due to deteriorated aileron bearings and/or the manner in which sealant to spanwise wing skin seams associated with wing anti-ice is applied. The aircraft had been recently repainted and the sealant reapplied in a manner inconsistent with the requirements of that service bulletin. The sealant was removed and re-applied and one or more aileron mildly suspicious bearings replaced. Subsequent test flights were unable to reproduce the events which precipitated the report.
An HS-125 flight crew encountered moderate to severe airframe vibration while in cruise at FL400. The vibration ceased following a descent and disconnecting the autopilot; subsequently diverting to a nearby airport.