1936, 40 C on 90 C. Airmail, overprint in orange-red on a mixed franking with 30 C on 90 C on an airmail registered letter from "Zuerich Flugplatz 23. VIII. 37" to Bern, with arrival stamp on the reverse side from the following day, rare, certificate Liniger, (Zumstein No. F23, F24 a s Fr. 1. 200.-)