B747-100 Question
 

On the -100 series, behind the hump there is what can be described as a 'crickle'on the top of the fuselage.

Can anyone explain what this is and what it is for?

I may have the wrong "Crickle", but years ago I remember my ground Instructor saying their is/was provision for an Astro-dome (OK tracker!)
just aft of the Overhead escape hatch (Not kidding!), stick your head out (Not in flight) and have a look rearward, (Not 744/743) you may see the round panel that allow's for this installation.
about the size of a basketball hoop, maybe a bit bigger!

If it is a largish fairing right where the hump meets the fuse then it was an antenna ( possibly early attempt at SATCOM )
The round hole is a sextant mount ( hard to REALLY convince yourself that you no longer needed a NAV ) which later became the smoke evac device.

In the photo on this shortcut, I am refering to the bulge/crinkle on the top of the fuselage above the letters d & a.

http://www.!!!!!!!!!!!!!!/open.file/522612/L/

The small dome was originally for an "astrotracker". When Boeing first offered the military the 747 one of the requirements was not INS but an astrotracker. It was a navigation device that locked onto the stars and provided heading, drift information to the navigator. I know they were in the B-52, SR-71 and some F-4s.

No doubt the airlines passed on that and went with INS instead.

That's the one Jet-A :ok:

Thanks guys - been wondering about that for YEARS!