WHILE CONDUCTING AN APCH TO ILS RWY 27L; ACR CAPT STATES HE OVERFLEW ACFT IN POS FOR TKOF ON RWY 22L. CAPT QUERIES CTLR ABOUT OP; BUT CTLR STATES EVERYTHING WAS LEGAL. CAPT HAS SERIOUS SAFETY CONCERNS REGARDING THIS TYPE OF OP. REDUCED VISIBILITY AND WX WERE FACTORS.

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WE WERE INSIDE THE OM ON A RWY 27L ILS TO ORD. TWR CLRED ANOTHER ACR TO TKOF IN FRONT OF US ON RWY 22L. FOR UNKNOWN REASONS THAT ACFT DELAYED THEIR TKOF. CONTRIBUTING FACTORS INCLUDED REDUCED VISIBILITY DUE TO LCL SNOW SHOWER AND NUMEROUS OTHER DEPS WAITING TO GO. WHEN OTHER ACFT FINALLY INITIATED TKOF ROLL; OUR ACFT WAS ON SHORT FINAL. THIS RESULTED IN OUR ACFT PASSING OVER THE TAIL OF THE DEPARTING ACFT WITH LESS THAN 200 FT VERT SEPARATION. TWR NEVER MODIFIED OUR LNDG CLRNC OR OTHER ACFT'S TKOF CLRNC. WHEN I QUESTIONED THE CTLR REGARDING THE INCIDENT; HE TOLD ME EVERYTHING WAS 'LEGAL' REGARDING THE OP. I HAVE SERIOUS CONCERNS REGARDING THE SAFETY OF THIS TYPE OF OP. CORRECTION ACTION: DURING PEAK TFC TIMES AND INTERSECTING RWY OPS; MORE STRINGENT SPACING REQUIREMENTS SHOULD BE USED FOR THIS PARTICULAR RWY CONFIGN. CALLBACK CONVERSATION WITH FACILITY SPECIALIST REVEALED THE FOLLOWING INFO: CALLED FACILITY SPECIALIST TO OBTAIN FURTHER INFO CONCERNING ACFT LNDG RWY 27L WITH ACFT IN POSITION ON RWY 22L. AN ACFT MAY BE IN POSITION RWY 22L ONLY S OF TXWY Q WHEN AN ACFT IS LNDG ON RWY 27L.