Mauchan to SA in c 1936

[Gillian Mauchan]

Hi

I have been trying to find the records of when my father arrived in South Africa. All I know is that he came with his mother and sister by sea in the mid 1930's - his father may or may not arrived on the Flying Boat which commenced service to the Vaal Dam in 1937.
I have looked on the Passenger list site and there are no passenger records for them at ths time (there are later records for his mother, father and sister in the 1950's).
His name was Andrew Mauchan, sister Sheena parents Andrew and Margaret. They previously lived in Airdrie where the two kids were born. I have anecdotal evidence that Andrew snr embarked on the Flying Boat from London so it is possible that the rest of the family may have sailed from there

Any ideas as to where I can look?

Gillian