[2] This aircraft differed from the B.E.2 in eliminating welded joints and complex metal components in the structure, and having greater dihedral on the upper wing.

[7] Aircraft following this initial batch were completed to a revised design, with a new fin and rudder, its leading edge straight and lacking the earlier comma shaped horn balance, and powered by the Renault-related but more powerful 90 hp (67 kW) RAF 1a engine.

[2] Both crew were placed in a single, extended cockpit with the pilot forward,[2] allowing the observer a more effective field of fire, although in the event few F.K.3s were flown with armament.

Armstrong Whitworth were given a contract to build 150 aircraft with another 350 being built by Hewlett & Blondeau Limited at Luton.

Some of the early batch had twin high exhaust pipes that exited above the upper wing in B.E.2 style, but these were later replaced with rams' horns forward stubs.