Why sit on the Left?

[GrahamB]

It's down to architecture not swords. Airfield infrastructure was originally designed to be on the south side of airfields so that ground staff didn't habitually look into the sun when looking over the field. Since the northern hemisphere prevailing winds are s'westerly the pilot sat on the left to be able to communicate with ground staff while on the 'runway'.

If aeroplanes had developed in the southern hemisphere the pilot would sit on the right.

Weren't most early airfields build when aircraft were single seat or tandem configuration?

[eltonioni]

Clearly it doesn't matter which side you sit on in a single seat or tandem aeroplane.