The airplane departed Buenos Aires at 05:15 on a regular flight to R¡o Cuarto. It climbed to the cruising altitude of 4500 feet. At 07:03 the crew contacted R¡o Cuarto Tower and obtained weather information. Weather was below minima, but the crew decided to attempt an IFR approach and began their descent. The airplane descended below MDA until it flew into terrain. PROBABLE CAUSE: “The decision of the pilot to descend en route, without justifiable reason, below the minimum altitude prescribed for a night flight, and in weather conditions which made it his duty to follow IFR procedure a contributing cause probably being an error between control tower and aircraft in the transmission or interpretation of barometric pressure of QFE and QNH values.”