US: PANAM Airmail labels

Here is a very rare error label from PANAM (Pan American Airways). It's not yet listed in Mair's catalogue.

Misprint: "BY PAN AMERICAN AIR MAIL SEKVICE"

Year: 1944, Gummed. Günter Mair's catalogue no: - USA-B-26c, perforated 11, sheets, 
black/light green-grey, 6******