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Nowadays they are no longer needed but why do they cover it up like in this photo? 737 What is the purpose and why aren't they used anymore?

Source

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They are mentioned in this discussion about cockpit windows – fooot Feb 10 at 15:44
up vote 24 down vote accepted

Wikipedia answers this on the Boeing 737 page:

Most 737 cockpits are equipped with "eyebrow windows" positioned above the main glareshield. Eyebrow windows were a feature of the original 707 and 727. They allowed for greater visibility in turns, and offered better sky views if navigating by stars. With modern avionics, they became redundant, and many pilots actually placed newspapers or other objects in them to block out sun glare. They were eliminated from the 737 cockpit design in 2004, although they are still installed at customer request. These windows are sometimes removed and plugged, usually during maintenance overhauls, and can be distinguished by the metal plug which differs from the smooth metal in later aircraft that were not originally fitted with the windows.

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All of that except the "navigating by the starts" comment sounds about right. Celestial navigation is done with a sextant, which needs a dedicated sextant port -- not through aircraft windows. You most certainly are NOT "following a star," because unless you're pointing at Polaris, you'd be following a star that's moving in the sky! – Ralph J Feb 11 at 3:22

To add to Steve's correct answer, Boeing has historically designed aircraft with less than ideal visibility for the pilot. Case in point: Their first all-metal passenger aircraft, the Boeing 247. Its design was ahead of its time and prompted TWA to convince Douglas to build the DC-1 and -2, but was marred by two details: The wing spar was not below the cabin floor level; instead, Boeing expected passengers to climb over the spar on their way to their seat. Many airlines were less enthusiastic and rejected the aircraft in favor of the DC-2 and -3, which also offered more seats.

The second detail was the cockpit window: It was sloped forward, so the visibility in the upper hemisphere was severely restricted. In turns the pilots were basically flying blind. The idea was to angle the window glass such that the instrument lighting would not reflect in the glass, but Boeing soon realized that this was creating new problems, and from the 247D on the window was sloped aft.

Boeing 247

Forward fuselage of the Boeing 247 (picture source)

When the 247 was offered to Lufthansa, it was rejected for this particular reason. I guess Boeing engineers were very sensitive to get the visibility right after the 247.

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Forward sloping glass... it would be interesting to see what that does in a wind tunnel. – FreeMan Feb 10 at 18:13
2  
@FreeMan: It did indeed increase drag a bit, which was another reason to never repeat this design detail ever again. – Peter Kämpf Feb 10 at 20:44
    
I just realized what "glare-shield" probably means now ... I wonder if it was put in Boeing aircraft at about the same time? – Steve Feb 10 at 21:55
    
I'd always heard that the eyebrow windows were a holdover from the KC-135 fuselage design, where having them was valuable for seeing a tanker aircraft when being refueled. (Most KC-135 aircraft aren't plumbed as receivers, although variants like the EC-135 are.) Wondering if that's accurate, or urban legend. – Ralph J Feb 11 at 3:18
    
@RalphJ: The tanker requirement sounds valid. I make no claim that Boeing transferred the experience directly from the 247 to the 737 - there is too much of a gap. – Peter Kämpf Feb 11 at 20:15

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