Complex sentence: The plane was modified to fix problems experienced in the old A.3, however, when the plane was tested using two 440hp Lorraine-Dietrich 12db engines, the results were quite modest.
Split into simpler sentences: The plane was modified to fix problems experienced in the old A.3. However, when the plane was tested using two 440hp Lorraine-Dietrich 12db engines, the results were quite modest.