What was found
IN FLIGHT HEAVY SMOKE BEGAN TO ENTER CABIN. WE RECIEVED APU OIL PRESS CAUTION MSG RAN QRH FOR THAT AS WELL AS SMOKE OM CABIN. WE SHUT DOWN APU. NO AUTO SHUTDOWN. COMPLIED WITH WORK SCOPE (CABIN SMOKE) AND REFER TO AML 3354481-1 FOR THE REPLACEMENT OF THE APU. APU ASSY REQUIRES REPLACEMENT WITH A SERVICABALE APU REMOVED+REPLACED THE APU IAW JOB CARD #200-49-10-00. OPS +LEAK CHECK GOOD.