howard hughs signed envelope

[tedtable]

I have what to appears to be a Howard Hughs commerative envelope from the 1939 New York Worlds Fair.
The top left it has "1939 New York Worlds Fair.
Below that is a rubber stamp talking about Howard Hugh's 1938 Around the World record flight. Next to the stamp is Howard Hughs signature. There is a second rubber stamp about his co-pilot along with the co-pilots signature. There are 6 post marked stamps on the envelope from the countries Howard Hughs landed in during the record flight. Each post mark is 1938.
Any idea what this is?
Any idea what the value on this would be or where I could get it apprased?

thanks..
Ted

[D&b antiques]

I would suggest you' contact and autograph collector or a first day cover collector.