Engine oil level AW139
By Pratt & Whitney's maintenance manual a visual inspection must be carried out every 12 flight hours of both the oil level and the oil filter impending bypass indicator.
Normally your aircraft maintenance staff has written this into the AMS as a daily task (off shore we fly about 7 hours a day per aircraft). So there should be no need for the pilot's to open the engine cowlings after the inspection has been carried out.
If you have found the level low after a dry run then someone missed this item.