EMB145 FLC EXPERIENCE A LOSS OF CABIN PRESSURE AT FL350. AN EMER DSCNT IS STARTED; WITHOUT ADVISING ATC OF THE NATURE OF THE EVENT. A POTENTIAL CONFLICT ENSUES WITH ACR Y AT FL330. CREW DECLARES EMER AT FL220; HAD TURNED OFF COURSE DURING DSCNT. BOTH PLTS WERE LOW TIME IN ACFT.

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AT 35000 FT AUTOMATIC PRESSURIZATION CTLR FAILED. CABIN ALERT SOUNDED A 10000 FT WARNING. I PUT MY OXYGEN MASK ON AND WENT TO SWITCH TO MY MASK MICROPHONE. CAPT WAS FLYING AND INITIATED AN EMER DSCNT. HE PUT HIS MASK ON AND PUT THE CTLR INTO MANUAL TO CTL CABIN. WE LEVELED AT 22000 FT MSL WITH CABIN UNDER 10000 FT. WE DECLARED AN EMER AND DIVERTED TO CLE INSTEAD OF CONTINUING ON TO MKE. NO DAMAGE; NO INJURIES. CAPT MADE ALL THE DECISIONS. CAPT WROTE UP THE PRESSURIZATION AUTO CTLR. SUPPLEMENTAL INFO FROM ACN 370496: EXECUTED EMER DSCNT. WHILE DSNDING WITH A SHARP L TURN AWAY FROM THE AIRWAY; A TCASII WARNING WAS GENERATED DUE TO A HEAD ON ACR ACFT AT 33000 FT. FLT WAS DSNDING IN A RATE OF APPROX 6500 FT AND WENT THROUGH 33000 FT IN ABOUT 20 SECONDS. REACHING 22000 FT AN EMER WAS DECLARED. AFTER CONSULTING WITH DISPATCH; A DIVERSION WAS MADE TO CLE HOPKINS ARPT TO SWITCH ACFT. ACCORDING TO ATC CTLR I SPOKE WITH THE NEXT DAY; FEW ATTEMPTS MADE BY ATC TO WARN ME OF THE ACR FLT. WHILE DSNDING; I ATTEMPTED TO CTL THE CABIN AND ESTABLISH COM WITH MY FO AND ATC WHILE MY FO PULLING THE CHKLIST TO DETERMINE THE PRESSURIZATION PROB. MY OBSERVATION FROM THE WHOLE EVENT; IS THAT ATC SHOULD HAVE VECTORED ACR IMMEDIATELY RATHER THAN TRYING TO ESTABLISH A VERIFICATION WHETHER I AM DSNDING OR IT IS MODE C ERROR.