Rolls-Royce RB211-535E4 is a three-spool turbofan variant in the RB211 family for the Boeing 757. Rolls-Royce documents the E4 product across 40,100–43,100 lbf takeoff ratings; Boeing's 757 planning data assigns 40,100 lbf to the base RB211-535E4, while the exact -37, B-37, and C-37 siblings remain separately modeled.