Re: Cockpit Windows

Date:         20 Jan 98 01:29:33 
From: (C. Marin Faure)
Organization: Northwest Nexus Inc.
References:   1 2
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In article <airliners.1998.40@ohare.Chicago.COM>,
ae562@FreeNet.Carleton.CA (Eric Thomas) wrote:

> Seth Heckard ( writes:
> > Pardon me if this is a stupid question, but why do older planes (such as
> > a Boeing 707, 727, or 737, and a DC-8 or -9 and MD-80) have an extra
> > cockpit window (or two) on top of the main row of cockpit windows?  And
> > why do newer, but similarly sized planes such as the A320 family and the
> > 757 have just one row of cockpit windows?
> The upper cockpit windows were installed so that pilots could have the
> option to navigate by the stars.  Also, when flying near the North Pole, a
> compass tends to be unreliable, which makes cockpit sky windows all the
> more necessary in order to use a sextant (naviagational tool).  However,
> in this day and age of GPS, the need for these ceiling windows has
> diminished.  Therefore, modern aircraft, especially commercial airliners,
> tend not to have these extra windows as high tech naviagational equipment
> has mostly eliminated the need for navigation by stars.

I'm not sure this is correct.  Aerial sextants require a bubble window, as
I believe the optics have to protrude above the skin of the fuselage.  You
can see these bubble windows on a host of older airplanes from the B-17
(it's on top of the nose in front of the windshield) to some models of the
707 (I believe it's over the aft portion of the flight deck).  I believe
the eyebrow windows were installed simply to improve visibility in a turn
and to let more light into the flight deck for map reading, etc.  As
flight deck instrumentation and displays became more and more
sophisticated, the need for eyebrow windows went away.  Also, with the
advent of CRT displays, the last thing you want on the flight deck is
light reflecting off the panel.  The new LCD displays are not degraded
nearly as much by extraneous light as CRT displays, by the way. Also, as
planes went to 2-pilot crews, it became desirable to put any overhead
controls as close to the pilots as possible, and the eyebrow windows may
have taken up space the designers wanted to use for something else.  I
suspect one reason the 737 has stayed with eyebrow windows is to avoid the
expense of changing the manufacturing tooling.  There may be structural
reasons to retan the windows as well, but I don't know what they are.

C. Marin Faure
  author, Flying A Floatplane