An emergency door opening mechanism for use with a locking mechanism of a pneumatic cylinder/differential engine for a power-operated door, said pneumatic cylinder/differential engine including a pair of aligned cylinders (1, 2) and a pair of associated pistons (4, 5) having a rack and pinion assembly including a gear, said rack and pinion assembly connected between and controlled by movement of said associated pistons (4, 5) for opening and closing of said door, wherein said locking mechanism includes a locking rod, a plunger associated with said locking rod for causing extension and retraction of said locking rod and a spring member associated with said plunger for maintaining said plunger and locking rod in an extended position for contacting and locking said gear during a "door closed" position, said emergency door opening mechanism comprising: (a) a series of cams (26, 27) associated with said locking mechanism comprising a first cam, a second cam in rotational engagement with said first cam and a torsion spring cooperating with said first and second cams, said second cam having a portion in contact with said spring member of said plunger and rotation of said first cam causing rotation of said second cam and compression of said spring member to retract said plunger and said locking rod with respect to said gear; (b) an emergency cable for applying a force to said first cam causing said series of cams (26, 27) to rotate and cause said locking mechanism to be released during emergency door opening; and (c) an air dump control lever associated with said series of cams (26, 27) and an air dump valve controlled by said air dump control lever for releasing air pressure from said pneumatic cylinders upon rotation of said series of cams (26, 27) during emergency door opening wherein release of air pressure enables a manual opening of the doors; (d) said first cam includes a beak portion and a notch portion located below said beak portion and said second cam includes a finger portion which rests within said beak portion prior to an emergency door opening command and moves to said notch portion upon rotation of said first cam during an emergency door opening sequence thus jamming said first and second cam together thereby maintaining the locking rod and plunger in a retracted position with respect to said gear. (a) a series of cams (26, 27) associated with said locking mechanism comprising a first cam, a second cam in rotational engagement with said first cam and a torsion spring cooperating with said first and second cams, said second cam having a portion in contact with said spring member of said plunger and rotation of said first cam causing rotation of said second cam and compression of said spring member to retract said plunger and said locking rod with respect to said gear; (b) an emergency cable for applying a force to said first cam causing said series of cams (26, 27) to rotate and cause said locking mechanism to be released during emergency door opening; and (c) an air dump control lever associated with said series of cams (26, 27) and an air dump valve controlled by said air dump control lever for releasing air pressure from said pneumatic cylinders upon rotation of said series of cams (26, 27) during emergency door opening wherein release of air pressure enables a manual opening of the doors; (d) said first cam includes a beak portion and a notch portion located below said beak portion and said second cam includes a finger portion which rests within said beak portion prior to an emergency door opening command and moves to said notch portion upon rotation of said first cam during an emergency door opening sequence thus jamming said first and second cam together thereby maintaining the locking rod and plunger in a retracted position with respect to said gear.