Design Eye Reference Point: – DERP -Some aircraft manufacturers provide reference points which the pilot uses while making the seat adjustments. These reference points could be something as simple as two balls affixed to the glare shield which the pilot must line up visually. In a two-pilot aircraft the reference points could be formed by three balls in a triangle and each pilot would adjust the seat until the respective reference balls line up. The intent, of course, is to have the pilot adjust the seat in order for the eyes of the pilot to be at the optimum location for visibility, inside and outside the cockpit, as well as the correct position for access to the cockpit switches and knobs. The engineering that results in the manufacturer placing these balls on the glare shield is called ERGONOMICS. This optimum position for the pilot’s eyes is referred to as the Design Eye Reference Point.
If there is no information on the design eye reference point in the aircraft operating manual, then it is suggested that the pilot could write the manufacturer and request the information. Failing that, the following guidelines should be considered when attempting to locate the correct seat placement (height, as well as fore and aft placement):
(a) all flight controls must be free of restriction throughout the full travel of the controls;
(b) flight instruments and warning lights must be visible to the pilot without being obscured by items such as the top of the glare shield;
(c) forward out-of-the-cockpit visibility should be sufficient to ensure that things such as the nose of the aircraft do not block the view of the pilot, especially during a normal approach and landing; and
(d) the chosen seat position should be comfortable for the pilot.