Originally Posted by number_6
No airline used the top deck for a lounge after the SUD (stretched upper deck) was introduced. All of the non-SUD 747s have been scrapped by now. The original 747 had space for only 4 seats upstairs, thus the desire to use it as a lounge instead. I think one airline used it as crew quarters, not for pax use. This was before they got the crew quarters in the tail on the later 747 designs.
Not quite. There are still a few passenger 747-200s that come through London Heathrow regularly on scheduled flights, Iran Air and Pakistan International can be seen often, also Syrianair 747SPs that have the same upper deck arrangement. They have put business-class seats up top.
The first airline to fully seat the 747 was Canadian charter carrier Wardair, who got their first 747-100 in 1973. They put economy 3+3 seating up there, about 24 seats (4 rows) all told.
I've never heard of all-crew seating up there (except on freighters), possibly a misinterpretation of the later crew compartment.
Here is a picture of a fully-Y seated 747 original-size upper deck, in this case an Iran Air 747SP taken a couple of years ago. This aircraft has been through Heathrow in recent times as well. In this case 24 seats are visible, as well as a small galley.