Flight Deck Cutoff Angle - Forward Visibility
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Joined: Jan 2004
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From: L'Alpe D'Huez
Flight Deck Cutoff Angle - Forward Visibility
Hello all.
Looking for some generic numbers to describe the loss in forward visibility if a pilot seated X cm too low in cockpit when approaching minima on ILS.
ie.. if a pilot is seated 5cm too low, what reduction in forward visibility would they experience? (Ie from 800m for CAT I at 300 feet).
Looking for some generic numbers to describe the loss in forward visibility if a pilot seated X cm too low in cockpit when approaching minima on ILS.
ie.. if a pilot is seated 5cm too low, what reduction in forward visibility would they experience? (Ie from 800m for CAT I at 300 feet).
Joined: Jan 2008
Posts: 1,269
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From: Denver
Capt Fathom's suggestion is good for a specific aircraft type (assuming one has the documents).
For a GENERIC ESTIMATION, this GENERIC document on the problem provides some dimensionless diagrams that may help figure a GENERIC geometry. Just choose and apply reasonable dimensions to the diagrams (eye distance from panel or other obstruction horizontally; pitch angle of aircraft on 3° glideslope (usually about 2-3° nose-up); actual height and slope of glareshield; and so on.
Of note, many modern aircraft (as you likely know) have eye reference indicators above the glareshield, to ensure correct seating (height above and distance from, the cockpit panel) for a correct eye position. And recent aircraft, originally designed in the glass-cockpit era, now have less-tall instrument panels to give pilots better downward vision (no doubt accounted for in the eye reference indicator's construction).
Also of note, it mentions just how a pilot could end up 5cm low even if their eye position was correct at the beginning of the flight - slouching from muscle fatigue after a long flight.
https://skybrary.aero/sites/default/...shelf/4247.pdf
For a GENERIC ESTIMATION, this GENERIC document on the problem provides some dimensionless diagrams that may help figure a GENERIC geometry. Just choose and apply reasonable dimensions to the diagrams (eye distance from panel or other obstruction horizontally; pitch angle of aircraft on 3° glideslope (usually about 2-3° nose-up); actual height and slope of glareshield; and so on.
Of note, many modern aircraft (as you likely know) have eye reference indicators above the glareshield, to ensure correct seating (height above and distance from, the cockpit panel) for a correct eye position. And recent aircraft, originally designed in the glass-cockpit era, now have less-tall instrument panels to give pilots better downward vision (no doubt accounted for in the eye reference indicator's construction).
Also of note, it mentions just how a pilot could end up 5cm low even if their eye position was correct at the beginning of the flight - slouching from muscle fatigue after a long flight.
https://skybrary.aero/sites/default/...shelf/4247.pdf
Last edited by pattern_is_full; 18th March 2023 at 17:15.
Joined: Dec 2003
Posts: 2,349
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From: Tring, UK
Interesting link but it seems a bit Airbus specific. I find Boeings tend to put you so far forward if you line up the little balls, or the rudder adjuster and the yoke markings, it becomes difficult to use the yoke fully and it feels rather uncomfortable. YMMV.
Joined: Sep 2016
Posts: 937
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From: USA
You could do the math on this (and I'm almost bored enough to do it just for fun) but the visibility lost from seating position is off the near end, while atmospheric conditions (the "visibility" on an approach around minimums, etc) is at the far end. So I don't see the related applicability. If you can't see the runway because of the fog, sitting higher won't help.
Joined: Jun 2001
Aviation Qualifications: ATPL
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Likes: 4,429
From: 3rd Rock, #29B
Hello all.
Looking for some generic numbers to describe the loss in forward visibility if a pilot seated X cm too low in cockpit when approaching minima on ILS.
ie.. if a pilot is seated 5cm too low, what reduction in forward visibility would they experience? (Ie from 800m for CAT I at 300 feet).
Looking for some generic numbers to describe the loss in forward visibility if a pilot seated X cm too low in cockpit when approaching minima on ILS.
ie.. if a pilot is seated 5cm too low, what reduction in forward visibility would they experience? (Ie from 800m for CAT I at 300 feet).
Capt Fathom's suggestion is good for a specific aircraft type (assuming one has the documents).
For a GENERIC ESTIMATION, this GENERIC document on the problem provides some dimensionless diagrams that may help figure a GENERIC geometry. Just choose and apply reasonable dimensions to the diagrams (eye distance from panel or other obstruction horizontally; pitch angle of aircraft on 3° glideslope (usually about 2-3° nose-up); actual height and slope of glareshield; and so on.
Of note, many modern aircraft (as you likely know) have eye reference indicators above the glareshield, to ensure correct seating (height above and distance from, the cockpit panel) for a correct eye position. And recent aircraft, originally designed in the glass-cockpit era, now have less-tall instrument panels to give pilots better downward vision (no doubt accounted for in the eye reference indicator's construction).
Also of note, it mentions just how a pilot could end up 5cm low even if their eye position was correct at the beginning of the flight - slouching from muscle fatigue after a long flight.
https://skybrary.aero/sites/default/...shelf/4247.pdf
For a GENERIC ESTIMATION, this GENERIC document on the problem provides some dimensionless diagrams that may help figure a GENERIC geometry. Just choose and apply reasonable dimensions to the diagrams (eye distance from panel or other obstruction horizontally; pitch angle of aircraft on 3° glideslope (usually about 2-3° nose-up); actual height and slope of glareshield; and so on.
Of note, many modern aircraft (as you likely know) have eye reference indicators above the glareshield, to ensure correct seating (height above and distance from, the cockpit panel) for a correct eye position. And recent aircraft, originally designed in the glass-cockpit era, now have less-tall instrument panels to give pilots better downward vision (no doubt accounted for in the eye reference indicator's construction).
Also of note, it mentions just how a pilot could end up 5cm low even if their eye position was correct at the beginning of the flight - slouching from muscle fatigue after a long flight.
https://skybrary.aero/sites/default/...shelf/4247.pdf
For off nominal seating, go measure your eye to coaming distance and apply a 1:60 for the quick solution, using the basic data from the FCOM, or do the trig. The eye height directly affects the visual cutoff but also the segment of observed surface, and that has issues with perception of rates. pitch attitude (speed/configuration/wind component) alter the cutoff as well. approximately each 5 kts changes the attitude by 1 degree... Every transport has a reference eye height, it is a design requirement and found in the AC 25-773-1 4(b) to meet the requirements of the Part. §25.773(d)
