Spain: Aerogramme with Special Postmark for UPU 75th Anniversary

This is Greiner #10c, the rare variant with overlay type B (light-grey, with wide sealing flap angle).

The aerogramme was cancelled with a special postmark commemorating the 75th anniversary of the UPU (Universal Postal Union) in 1949. Philatelic usage.

Reference:
Greiner/Greiner, Aerogramme von Europa, 3e, 1993