Austria, Scott 340, C17, C19, C27 on 1933 Glider Mail Cover GRAZ, AUSTRIA to MARIBOR, YUGOSLAVIA.  Three strikes of magenta GRAZ-MARIBPR special GLIDER MAIL cancels dated May 1933 tie all 4 stamps, triangular POSTNO-JAD / GRAZ - MARIBOR Flight Cachet in purple, two GRAZ cds cancels one day apart, AEROCLUB of Maribor handstamp at LL corner, black on blue Air Mail etiquette, addressed tp Zagreb. Reverse: Unsealed flap, minor mount remnant. A fresh and clean cover. Size: 7" x 4½".