What was found
VHF 2 BELLY MOUNTED ANTENNA VIBRATIONS FELT BY FLIGHT CREW. EXTENDED NOSE (KIT 130-4050) AND EXTENDED NOSE EO/IR LIFT (KIT 130-4051) INSTALLED. THE VHF 2 ANTENNA VIBRATES DURING FLIGHT WITH THE EO/IR TURRET IN THE EXTENDED POSITION. THE VIBRATION IS BELIEVED TO BE CAUSED BY VORTEX SHEDDING FROM THE TURRET JUST FORWARD OF THE ANTENNA. THE VIBRATION STOPS ONCE THE TURRET IS RETRACTED. THIS WAS VERIFIED BY VIDEO RECORDING MADE BY AN EXTERNALLY MOUNTED CAMERA AFT OF THE ANTENNA. THE VIBRATION WAS CLEARLY VISIBLE WITH CORRESPONDING SKIN DEFLECTIONS. IN AN ATTEMPT TO CORRECT THIS DISCREPANCY, THE NOSE GEAR DOOR RIGGING WAS CHECKED BY TEXTRON AVIATION INC. AND FOUND TO BE IN ACCORDANCE WITH TEXTRON AVIATION INC. ICA P/N 130-590031-0658, CHAPTER 32-20-05 AND KIT 130-4050-0009/-0027 INSTALLATION INSTRUCTION ITEM 22. A DOUBLER WAS INSTALLED BY TEXTRON AVIATION INC. UNDERNEATH THE VHF #2 ANTENNA. DURING SUBSEQUENT FLIGHTS, A REDUCTION OF THE AIRCRAFT SKIN DEFLECTIONS IS OBSERVED. THE VIBRATION IS STILL VISIBLE ON THE ANTENNA AND CAN BE FELT BY FLIGHT CREW.