What was found
ON THE GND WITH APU RUNNING FOR ABOUT 5 MINUTES, TAIL CONE BLD LEAK AMBER CAS MSG CAME ON. WITHIN 30 SECONDS COCKPIT & CABIN FILLED WITH SMOKE. INSPECTED TAIL CONE COMPARTMENT, NO SMOKE DETECTED. POWERED UP APU & RAN ENVIRONMENTAL SYS FOR 30 MINUTES, ALL INDICATIONS NORMAL, NO SIGNS OF SMOKE, HOWEVER DID OBSERVE LARGE AMOUNTS OF WATER VAPOR COMING FROM GASPERS DUE TO TEMP & HUMIDITY IN AREA, TIST, NO FLIGHT FAULTS FOUND, NO BLEED LEAKS FOUND IN TAIL CONE AREA, ALL CHECKS PERFORMED IN MAX COOL MODE IAW MM.