<p>Intriguing shot.  I can make out "1717 New York" on the plane, and this has now been identified as the Heinkel He12 on board the German liner the Bremen. This cannot be the first flight as it was only when it arrived that it was christened "New York".  But it must be some time between July 1929 and the final flight in October 1931.
</p><p>From <a rel="nofollow" class="external text" href="http://celticowboy.com/Mail%20Service%20From%20German%20Passengerships%20Bremen%20And%20Europa.htm">celticowboy.com/Mail%20Service%20From%20German%20Passenge...</a>:
"On 22 July, 248 miles out from New York, [Captain Jobst] von Strudnitz was catapulted into the air in the He 12 which carried 660 lbs of mail. The Heinkel landed 2.5 hours later in New York Harbor where it was met by the mayor and other officials who christened the plane New York. During the return voyage the aircraft was launched near Cherbourg on 1 August, while still in the English Channel, and it reached Bremerhaven more than 24 hours before its parent vessel after a 600-mile flight. The 18,000-letter express mail cargo was immediately flown on to Berlin in a waiting Lufthansa aircraft. Eight further flights were made during the year. "
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One of many images that I am slowly importing from my whatsthatpicture.com website.  See the original at <a rel="nofollow" class="external text" href="http://www.whatsthatpicture.com/index.php?q=gallery&amp;g2_itemId=3190">www.whatsthatpicture.com/index.php?q=gallery&amp;g2_itemI...</a>
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/24469639@N00">whatsthatpicture</a> from Hanwell, London, UK
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/whatsthatpicture/3732269188/">Seaplane air mail service Heinkel HE12 D-1717 "New York"  aboard the Bremen</a>