Monmouth Airlines Flight 98 departed Wilkes-Barre at 22:53 for a short IFR flight to Allentown. Allentown Approach Control cleared the flight for a VOR approach and instructed the pilot to report when it was 12 miles North of the Allentown VOR. At 23:07, upon receiving the flight’s position estimate, Allentown Approach Control cleared Monmouth 98 for a VOR approach to a landing on runway 06. Monmouth 98 was requested to report when inbound over the Allentown VOR. The Beech then collided with the ridge of Blue Mountain at an elevation of 1540 ft (470 m). PROBABLE CAUSE: “The pilot’s nonadherence to approved approach procedures for executing a nonprecision instrument approach in instrument flight conditions. The Board further finds that there is a high degree of probability that the extensive on-duty time and actual instrument flight time prior to this accident resulted in the fatigue of both pilots and affected their judgment and decisions during the approach.”