If experiencing a severe nose wheel shimmy, what initial action should you take?

Experiencing a severe nose wheel shimmy indicates that the nose gear is vibrating excessively, which can happen for various reasons, such as improper alignment or tire issues. The correct initial action of lifting the nose serves to relieve weight from the nose wheel, which can help reduce the severity of the shimmy. By raising the nose, you decrease the load on the nose wheel, thus allowing it to stabilize and potentially eliminate or lessen the vibration.

Other options do not address the underlying issue effectively. Increasing throttle can worsen the situation by increasing speed and possibly intensifying the shimmy. Turning the aircraft may lead to a loss of control if the shimmy is severe, while applying brakes immediately could cause the aircraft to nose over or exacerbate the shimmy due to differential brake forces. Therefore, lifting the nose is the most prudent first step when dealing with a severe shimmy.