Senna
Took my 8 wk old pup home in the aeroplane - he was sedated and sat in a doggy transport box.
When he was a couple of years old and 40 kilos used to put him in the back of the Seneca (take out the rear two seat) and tied his collar to the cargo lashing points.
He was pretty cool about the whole thing but have read that dogs' ears are pretty sensitive to pressure change therefore used to climb out quite shallowly and IIRC never exceeded 3,500'.
Only concern at the time was injury to him if I screwed up a landing.
Last time he flew was in a 747!
Stik