When a dehumidifier is installed during an extended MRG lay-up, what relative humidity must it maintain within the MRG casing?

The correct answer is that the dehumidifier must maintain a relative humidity of less than 35 percent within the MRG (Main Reduction Gear) casing during an extended lay-up. Maintaining this specific humidity level is crucial because it helps to prevent condensation from forming inside the casing. High humidity can lead to moisture accumulation, which may cause corrosion and other forms of deterioration to the internal components of the MRG. By keeping the humidity below this threshold, the equipment can be better protected and its longevity ensured during periods of inactivity.