The One-Eleven prototype , flown by test pilot Mike Lithgow , crashed on 22 October during stall testing , with the loss of all on board . The investigation led to the discovery of what became known as deep stall or superstall , a phenomenon caused by reduced airflow to the tailplane caused by the combined blanking effects of the wing and the aft-mounted engine nacelles at high angles of attack , which prevents recovery of normal ( nose-down ) flight . To prevent such stalls , BAC designed and added devices known as stick shakers and stick pushers to the One-Eleven 's control system . It also redesigned the wing 's leading edge to smooth airflow into the engines and over the tailplane . The specially modified aircraft used for testing this problem is now preserved at Brooklands Museum
crashed on 22 October
1963 BAC One-Eleven test crash
BAC One-Eleven