What was found
AIRCRAFT WAS GROUNDED: STRONG ODOR ON TAKEOFF, SIMILAR TO BURNT FOOD OR PLASTIC. FLIGHT ATTENDANTS CONFIRMED THE OVENS WERE OFF AND THEY ALL SMELLED THE SAME SMELL THROUGHOUT THE CABIN. GOT BETTER AROUND FL 260 BUT LINGERED FOR REMAINDER OF THE FLIGHT. THE VERY STRONG ODOR RETURNED DESCENDING THROUGH 7000 FEET THROUGHOUT THE FLIGHT DECK AND CABIN. ALL FLIGHT ATTENDANTS REPORTED ODOR. A MIX OF CRAYON SMELL, HOT RUBBER AND PLASTIC. MAINETNANCE ACCOMPLISHED SMOKE ODOR FUMES TROUBLE SHOOTING AND A DECONTAMINATION OF THE ENVIRONMENTAL CONTROL SYSTEM PER TASK CARDS 26L00021001, 26L00021002 & 26L00021014. A SATISFACTORY LEAK / OPERATIONAL CHECK WAS ACCOMPLISHE DWITH NO ODORS OR FAULTS NOTED.