Which of the following is NOT correctly performed during a level speed change (LSC)?

Starting in slow cruise at 150 KIAS is not appropriately performed during a level speed change (LSC) because this maneuver typically begins in a normal cruise configuration. Normal cruise indicates a speed above the slow cruise range, generally around 200 KIAS or more. The purpose of the LSC is to demonstrate how to decelerate the aircraft while maintaining altitude and then stabilize at a slower indicated airspeed, usually transitioning from a faster cruise speed.

The other options accurately describe steps in performing a level speed change. Reducing power to approximately 31% helps facilitate the decrease in speed while allowing for altitude retention. Trimming for deceleration and stabilizing at 150 KIAS is a critical part of the maneuver to ensure the aircraft remains controllable as it slows down. Thus, understanding that starting in normal cruise is essential for an effective level speed change reinforces appropriate training procedures.