I was booking a flight on Delta's Boeing 747-400 flight, and saw a strange thing on the seat map. The back few rows (rows 63 to 66) were missing the middle seats. Namely, Row 63 went like this:

63A (space) 63C (aisle) 63D 63E 63F 63G (aisle) 63H (space) 63K

I am traveling with a companion; I prefer the window seat, and my companion prefers the aisle seat. If the space were indeed an empty space, choosing 63A and 63C sounds ideal. But are the middle seats really not there? Or is it reserved for pilots and other airline personnel? If anyone has any advice on this, I'd appreciate the information. Thanks!