What is true regarding S1 in relation to Vrot?

S1, also known as the decision speed, is critical for ensuring safe aircraft operations during takeoffs. In relation to Vrot, which is the rotation speed at which the aircraft should start lifting off the ground, S1 must be less than Vrot to allow for a safe takeoff.

When S1 is less than Vrot, it provides the pilot with a buffer. This buffer is crucial because if an engine failure occurs or any other emergency arises during the takeoff roll, the pilot has the opportunity to reject the takeoff safely before reaching Vrot. If S1 were to equal or exceed Vrot, the pilot would not have enough distance or time to stop the aircraft safely before attempting the rotation, increasing the risk of an accident.

In essence, having S1 be less than Vrot ensures that the pilot can make a decisive and safe choice regarding the continuation or aborting of the takeoff. This operational guideline is a fundamental part of safe takeoff procedures in aviation.