Does the court erred by failing to instruct the jury on the essential elements of armed robbery?

Fleming also contends that the district court erred by failing to instruct the jury on the knowledge requirement to sustain a conviction as an aider and abettor to armed robbery. "Where no objection was raised to a jury instruction at trial, reversal would be warranted only for plain error." See United States v. Boone, 951 F.2d 1526, 1541 (9th Cir.1991). The district court instructed the jury on all of the essential elements of armed bank robbery. See 18 U.S.C. 2113(a), (d) (1997). Fleming was charged as a coconspirator to armed robbery and not as an aider or abettor. Accordingly, the district court did not err by failing to instruct the jury on the knowledge requirement for an aider and abettor.