Early production aircraft had unequal span wings, similar to those fitted on the B.E.1, and at first there was no decking between the pilot and observer's seats, although this was added later. Sandbag loading tests revealed that the safety margin of the rear spar was somewhat less than that of the front; to remedy this, a revised wing was designed with a deeper rear spar, and consequently a different aerofoil section. Later production aircraft also had equal-span wings. These modifications were retrofitted to the majority of the remaining earlier production aircraft.