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Ishigami

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  1. Q = Quiet It simply means that ANVS is present and that the noise levels inside the cabin are lower. The Q was introduced to market this. Every Dash 8 since sometime around 1996 is a Q. The ANVS is series of microphones and actuators (ATVA: Active Tuned Vibration Attenuator) placed on several location of the fuselage. It also includes an accelerometer mounted underfloor, vibration transducer mounted on the reduction gearbox of each engine and a box to control it all the ANCU: Active Noise Control Unit which is also mounted under floor. The microphones pick up the noise inside the aircraft while the ANCU outputs certain vibration levels via the ATVAs depending on propeller RPM, cabin noise and their own location. The vibrations of the actuators and propeller are out of phase cancelling each other out thus leading to a quieter cabin. Nice “side” effect is that the structure is also stressed less since it oscillates less. I think there is really cool animation inside the CBT but I'm unable to find it on the web atm. The reason this system often operates in degraded mode or is even goes inop is that the system only works perfect if every part is operating and that means mostly every microphone, actuator and amplifier. (I've never seen a failed accelerometer or vibration transducer thus far) Once a certain amount of microphones, actuators or amplifiers fails the systems goes into degraded mode and when there are enough failures it goes inop. The reason your maintenance will not act immediately is that it is quite a lot of work. After all the actuators are mounted directly onto the fuselage via a small bracket. If you have to change one you have to disassembly the cabin in this area. The same goes for the microphones. They are placed all over the cabin and the most annoying ones are the ones behind side wall panels. Since there are so many ATVAs and mics chances are high that a few are U/S. There is only a inop indication for the crew. I imagine they never know when the system operates in degraded mode. For that to check you would need to access the maintenance panel above the wardrobe.
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