Where a plaintiff files suit against a common carrier for an injury sustained after exiting the conveyance while descending a staircase on a platform owned by the common carrier, the common carrier only owes the plaintiff an ordinary duty of care.The 1st District Appellate Court affirmed in part and vacated in part a decision from Cook County Associate Judge Thomas M. Donnelly and Circuit Judge John P. Callahan Jr.On Dec. 24, 2009, Martha Avila slipped and fell down a staircase at an elevated (L) station owned by the …