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Mrs. Bruce was the first female pilot to fly between England and Japan.
Literal
Mrs. Bruce [topic-は] England-Japan-interval [object-を] flew first [genitive-の] female pilot was.
A biographical sentence, encyclopedic in register. The relative clause 英日間を飛んだ ('flew the England-Japan interval') modifies 女性パイロット ('female pilot'). 英日間 is a compound: 英日 (England-Japan) + 間 (interval, space between) = 'the space between England and Japan.' The particle を on 英日間 is the 'path を' (traversing a space), same as 空を飛ぶ ('fly through the sky'). The copula であった is the formal literary past, matching the encyclopedic register. 'Mrs. Bruce' refers to Mary Bruce, who made a long-distance flight from England to Japan in 1930.