Reply received - Thanks !!:

15.2.2002 from Dave Mui, Chicago, USA
Per- the American Air Mail Catalogue lists a crash of 12/25/40 Pan Air do Brasil flight at Bahia Brazil.
It says a Sikorsky S-43 flying boat hit the top deck of a ship on landing on the Bay of All Saints and crashed into the water. Only a small amount of mail was recovered in water soaked condition. The illustration of the crash marking appears consistent with your cover. Cover is valued at $125.