280KG EACH for the 747 front windows ?
No, they don't weigh THAT much !! About 150lbs (68kgs)
I'm not that strong and I've moved plenty of 'em over the years, -200's, -300's, SP's and -400's. (Mostly with a helping hand though)
Personally, one of my favourite components of the 747. Beautifully designed, constructed and very reliable. Of course originally designed and built in the '60's by draftsman without CAD or any computers- fantastic curved glass !
Below is copied from the Maintenance Manual.
FLIGHT COMPARTMENT WINDOWS - DESCRIPTION AND OPERATION
1. General
A. Six windows are symmetrically located around the forward end of the flight compartment. The windows are designated right side and left side windows No. 1, 2, and 3, as shown on Fig. 1. The corresponding left and right windows are identically opposite assemblies.
B. All flight compartment windows are of laminated construction. The No. 1 windows, which are the pilots' windshields, consist of a greater number of laminations to withstand bird impact.
C. Pressure sealing is accomplished with a gasket or rubber-beaded seal molded to the windshield frame and the No. 2 and 3 window step cuts. An aerodynamic seal is accomplished by filling the gap between window edge and fuselage skin flush with aerodynamic smoother. This also serves as a weather seal for keeping out moisture.
2. No. 1 Windows
A. The left No. 1 window is the captain's windshield. The right No. 1 window is the first officer's windshield. The left and right windshields are opposite assemblies and installations.
B.
Each windshield weighs approximately 150 pounds and consists of transparent layers secured between a Z-frame and mounting ring. The layer construction allows for thermal differentials and prevent crack propagation between the structural layers. The Z-frame and mounting ring attach to the fuselage structure surrounding the windshields.
C. Two types of No. 1 windows can be installed: a five-layer soda-lime glass laminate or a five-layer tempered glass and soda-lime glass laminate. Windows with a P prefix serial number are constructed of five basic layers: a glass outer layer, an interlayer, a glass structural ply, an interlayer and a glass crew shield. Windows with a T prefix serial number are constructed of five basic layers: an outer tempered glass layer, an interlayer, a glass structural ply, an interlayer and a glass crew shield, which is a structural ply. New and replacement T prefix No. 1 windows have outer glass ply with greater thickness for added strength.
D. The inner face of the face ply is covered with a conductive coating, which is part of the antifogging and anti-icing systems. Bus bars, embedded in the windshield layers, contact the conductive surface near the top and bottom of the windshield. Two temperature control sensors are laminated into the windshield adjacent to the conductive coating. Only one control sensor is used; one is a spare that is used only if the other fails. Wires from the bus bars and sensors extend through the windshield laminations to the terminals on the inner face.
Confusion can occur when the wrong part of the manual is referenced - my job is to make sure that this doesn't happen!! 2 quotes below from the removal/installation task.
One relates to the equipment required (generic in nature), the other to the window itself.
" Equipment and Materials Required
A. Crane equipped with 40-foot boom and capable of lifting 500 pounds or equivalent
B. Mobil mechanical lift (capable of extending to a height of 35 feet) or overhead
crane capable of lifting 500 pounds (i.e 227kgs) "
"
CAUTION: USE CARE WHEN HANDLING THE WINDSHIELD ASSEMBLY. IT WEIGHS APPROXIMATELY 150 POUNDS AND IS A HIGH COST ITEM. "