Mittelholzer started in Zürich on 7 December 1926, flying via Alexandria and landing in Cape Town on 21 February 1927.

[2][3] In 1931, Mittelholzer was appointed technical director of the new airline called Swissair, formed from the merger of Ad Astra Aero and Balair.

[5] He died in 1937 in a climbing accident on an expedition in the Hochschwab massif in southwest face of Stangenwand in Styria, Austria.

[6] His mortal remains were cremated and buried in the urn vault of his mother Elizabeth "Elise", née Grunder (1856-1928), in the columbarium halls of the Feldli cemetery in St. Gallen.

The urns containing the ashes of his father Walter Ulrich (1860-1945), a baker, and those of three of his four sisters - Anna (1885-1969), Clara (1886-1963) and Gret (1899-1997) - were later buried there as well.