Austria: Early Air Letter Form Franked at Full Air Mail Letter Rate

Air letter form (most likely of US origin) sent from Vienna (15. III. 48) to New York, US.
 
Franked at 2.20 S (air mail letter rate), which is 1 S UPU letter rate plus 1.20 S air mail surcharge (5 g of weight).
 
Foreign air letter forms used in Austria that early are quite uncommon.