The first flight of the A340 occurred on 21 October 1991, marking the start of a 2,000-hour test flight programme involving six aircraft. From the start, engineers noticed that the wings were not stiff enough to carry the outboard engines at cruising speed without warping and fluttering. To alleviate this, an underwing bulge called a "plastron" was developed to correct airflow problems around the engine pylons and to add stiffness. European JAA certification was obtained on 22 December 1992; the FAA followed on 27 May 1993.