View Full Version : Low Visibility Ops - sitting too low in flight deck calculaiton

17th Mar 2023, 23:51
Hello smart ppruners.

Looking to calculate the theoretical the of visibility if a pilot sits 1 cm too low in flight deck on an ILS approach.

ie If in the correct position at the minima of a CAT I ILS a pilot can see exactly 800m, using an average cutoff angle, roughly how much less would forward visibility would they see if they seated 1cm too low?

Please help if suitable. Any diagrams would also be most appreciated.

tubby linton
18th Mar 2023, 20:15
You are talking about less than half an inch. Sitting up straight rather than slightly slumped would make a difference but you are looking for lights and the runway.

Genghis the Engineer
18th Mar 2023, 22:16
I've never seen DEP (Design Eye Position) used with that degree of precision in civil aircraft certification.

But with the geometry you're describing anyhow, either the visibility is unaffected, or you can no longer see ahead because of the coaming. There's no intermediate position that I can see.


Sleeve Wing
17th Apr 2023, 15:04
I think the main consideration is that your seating position should be exactly the same for all low vis approaches. This should enable you to see the first ground contact at minima or above, showing the same, expected "picture".
A long time ago KLM and also British Midland used a simple, small metal aperture on the end of a chain suspended from the cockpit overhead. This was used to move your seat to line up the eye with the aperture and thus achieve the same personal position every flight and of course the same eyeline. Such positioning provided a consistent and expected "picture" of both the approach and the instrument panel.
Having said that, STILL FLY YOUR INSTRUMENTS to maintain the ILS glide path until you have sufficient clear eyeline to carry out a safe landing. The first tendency on becoming visual will stiil be to dip below the GP. This is because you will fly where your eyes automatically focus on the shorter visible distance ahead.