The design eye position, also known as eye datum or design eye reference point (DERP) is one of the key aspects of cockpit design. It is used to size the cockpit windows and defne the location of all the controls, displays and instruments.
Some aircraft manufacturers provide reference points which the pilot uses while making the seat adjustments. These reference points could be e.g. 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 is to have the seat adjusted so that the eyes of the pilot are at the optimum location for visibility, inside and outside the cockpit, as well as in the correct position for access to the cockpit switches and knobs.
When the pilots are properly seated and aligned with the eye reference point, they will have adopted the optimum position to operate the aircraft because they will:
- have all of the instruments and displays on the front panel are in their feld of view.
- be able to reach and operate all of the aircraft’s controls through their full range of motion or deﬂection with their seat harness fastened.
- have an optimal feld of view through the cockpit’s windows to see what is around them outside the aircraft.
- maintain the best cut-off angle that will provide the longest visual segment. This is especially important to get visual references during Low Visibility Operations.
- have an optimal view of the heau-up display (HUD), if one is installed.
Regulations require that aircraft manufacturers provide a means which will aid the pilots to position themselves with precision and allowing them to have the best point of view from their seat.
EASA CS 25.773 and FAA FAR 25.773 state that for nonprecipitation conditions, the following apply:
- Each pilot compartment must be arranged to give the pilots a sufficiently extensive, clear, and undistorted view, to enable them to safely perform any manoeuvres within the operating limitations of the aeroplane, including taxiing, take-off, approach and landing.
- Each pilot compartment must be free of glare and reflection that could interfere with the normal duties of the minimum flight crew. This must be shown in day and night flight tests under nonprecipitation conditions.
EASA CS 25.777 and FAA FAR 25.777 state that "The controls must be located and arranged, with respect to the pilots' seats, so that there is full and unrestricted movement of each control without interference from the cockpit structure or the clothing of the minimum flight crew when any member of this flight crew from 1.58 m (5ft 2 inches) to 1·91 m (6ft 3 inches) in height, is seated with the seat belt and shoulder harness (if provided) fastened."
A pilot seated in a position that is too low may experience the following:
- having diffculties to reach all of the system controls located on overhead panel.
- reduced situational awareness on the ground which may increase the risk of collision with airbridges, buildings, ground support vehicles or other aircraft on the ramp.
- inaccurate perception of the flight path during the final approach.
- have a blind area, reducing the cut-off angle and thus limiting the visual segment.
If seat position that is too high, the possible effects can be:
- inaccurate perception of the flight path during final approach
- impaired view of the instrument panel and in some cases, upper PFD and ND hidden from view
- operating the rudder pedals through their full range would be more diffcult
Position Adjustment and Best Practices
The ﬂight crew must adjust their seating position before the aircraft moves, typically before the pushback or engine start.
General adjustment procedure:
- Adjust the seat longitudinal and vertical position to align the eye-level with the eye reference indicator and also check that the glareshield does not obstruct the view the upper PFD and ND.
- Adjust the armrest to a position where the hand can grip the sidestick naturally without stretching the forearm and with a straight wrist. If the armrest is correctly adjusted, the forearm should rest comfortably on the armrest and the pilot will only need to move their hand and fngers to give the appropriate inputs to the sidestick.
- Adjust the pedals position using the adjustment lever. Ensure the pedals can be moved through their full range of motion.
Towards the end of a ﬂight, especially for long sectors, the pilot’s position may change due to muscle fatigue often causing them to adopt a position that is lower than at the beginning of the ﬂight. Therefore it is recommended to re-adjust the seating position before commencing the approach.
During the cruise ﬂight phase where the pilots’ eye level alignment is not as critical, pilots may adjust their seat to be out of the eye reference point position for increased comfort. To be able to face any unexpected situation, pilots should still ensure that they can reach all of the ﬂight controls and their view of the control panels is not impaired.