WAKE TURB ENCOUNTER BEHIND ANOTHER 737. NIGHT OP.

Narrative

I WAS PF OF A B-737-200 ON APCH TO ORD. I HAD THE AUTOPLT ENGAGED AND WAS UTILIZING THE CTL WHEEL STEERING MODE. WE WERE GIVEN A SPD ASSIGNMENT OF 170 KTS; AND SINCE THIS WAS BELOW CLEAN MANEUVERING SPD FOR OUR GROSS WT (96000 LBS) I SELECTED FLAPS 2 DEGS. WHEN CONFIGURED AND STABILIZED AT 170 KTS AND 4000 FT MSL; THE NOSE ABRUPTLY PITCHED UP 5-10 DEGS AND THE ACFT ROLLED 40 DEGS TO THE L. I DISCONNECTED THE AUTOPLT AND RIGHTED THE ACFT. BECAUSE THIS WAS OBVIOUSLY A WAKE TURB ENCOUNTER; I RPTED IT TO APCH CTL AND ASKED 'WHAT TYPE ACFT ARE WE FOLLOWING?' THE REPLY WAS 'A 737.' I SAW THE LIGHTS OF AN ACFT AND TCASII INDICATED IT WAS 2 1/2 - 3 MI IN FRONT. THE REMAINDER OF THE APCH AND LNDG WAS UNEVENTFUL. THE SEVERITY OF THIS ENCOUNTER SURPRISED ME; AND I THOUGHT THAT IT WAS A HVY OR A 757. ALTHOUGH I WAS FLYING ON AUTOPLT CLEAN MANEUVERING SPD I HAD MY HANDS LIGHTLY ON THE YOKE; AND WE STILL ROLLED PAST 30 DEGS. HAD I BEEN DISTRACTED BY LOOKING AT A CHART OR CHKING ENG INSTS; ETC; I COULD HAVE VERY EASILY ENDED UP ON MY BACK; AND THIS WAS FROM ANOTHER 737! CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR CALLED BACK AND STATED THAT HIS ACFT WAS IN-TRAIL BEHIND THE OTHER 737. HE HAD BEEN IN LEVEL FLT FOR ABOUT 1 MIN. THE OTHER 737 HAD BEEN SEQUENCED INTO A POS IN FRONT OF HIS 737. THE CTLR HAD NOT ISSUED A TA. SINCE IT WAS AT NIGHT; IT WAS DIFFICULT TO ESTIMATE THE ACTUAL DISTANCE IN SPACING. THE TCASII INDICATED A MINIMUM OF 2.5 MI AND A MAX OF 3 MI. IN RESPONSE TO THE QUESTION; 'WHAT WERE THE MOST SIGNIFICANT CONTRIBUTING CAUSES FOR THE WAKE TURB INCIDENT' THE RPTR STATED INADEQUATE SPACING OR SEPARATION BEHIND THE OTHER ACFT. THOUGH THE OTHER ACFT WAS NOT A HVY; THE 737 GENERATED A SURPRISING AMOUNT OF WAKE TURB. HE SAID HE COULDN'T THINK OF ANYTHING HE WOULD HAVE DONE DIFFERENTLY. IN ORD THE SPACING IS NOT ALWAYS UP TO SEPARATION STANDARDS. HE BELIEVES THE ATC SHOULD ADHERE MORE CLOSELY TO THE SEPARATION CRITERION.