During a period of dual training, the instructor noticed that the oil temperature was rising to an undesirable level and that the oil pressure was falling. He elected to carry out a precautionary landing on a short, disused agricultural strip, rather than flying 20 minutes back to the aerodrome. The student was to carry out a short field landing under the supervision of the instructor, who was to talk her through the exercise. At about the point of touchdown, the press-to-talk switch in the rear pilot compartment failed and the student was unable to hear any further instructions. She became apprehensive about the length of strip remaining and applied heavy braking, which the instructor was unable to overcome, and the aircraft nosed over. An inspection of the aircraft revealed that a cleaning rag, which had been missed during the daily inspection, had partially covered the oil cooler, rendering it less effective.
