I'm working my way through "On Glorious Wings", a collection of short stories
edited by Stephen Coonts.

In at least a couple of the stories from the first part of the 20th century,
there are references to airplane mechanics as "Ack Emma". I think the stories
where these references appeared had British authors, so it might be a Brit thing.

Why are/were airplane mechanics called Ack Emma?

Thanks,

Dave