 In 1954 , the RB.106 program was cancelled , necessitating the use of the backup Wright J67 engine instead . In 1955 , this engine was also cancelled , leaving the design with no engine . At this point , the Pratt & Whitney J75 was selected for the initial test @-@ flight models , while the new TR 13 engine was developed at Orenda for the production Mk 2s . 
