Learjet 55
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Engineer
Flight Crew Last 90 Days 60; Flight Crew Total 22000; Flight Crew Type 50
Aircraft Equipment Problem Critical
General Declared Emergency; General Maintenance Action
Aircraft
While descending through FL200 at 280 KIAS; a hum was heard; followed by a louder buzz; followed by an abrupt roll and yaw to the left. I reduced airspeed to about 180 KIAS and the control forces lightened considerably. We immediately declared an emergency and continued straight ahead to our destination which we deemed to be our closest suitable airport. We configured early for landing at about 6;000 MSL to insure we had sufficient altitude and airspeed for recovery in the event the aircraft became uncontrollable during the landing re-configuration process. We flew the approach at Ref+15 and made an uneventful; although abnormal; landing. Upon deplaning; we discovered the left-hand aft wing/body fairing partially separated from the aircraft. Repairs were accomplished at a Bombardier Service Center and it was determined that improper sealing of a wing/body fillet forward of the failed faring allowed excessive air pressure to enter the fairing cavity and blew it off.
A LJ-55 flight crew suffered the partial loss of the aft left wing body fairing.  Maintenance determined the failure was the result of improper sealing of the wing body fillet forward of the fairing allowing excessive internal air pressures to develop; resulting in the separation.