Why might a pilot flying under IFR request an altitude change?

A pilot flying under IFR, or Instrument Flight Rules, may request an altitude change primarily to comply with Air Traffic Control (ATC) instructions or to meet specific airspace requirements. These regulations are in place to ensure the safety and efficient movement of aircraft within controlled airspace. Air Traffic Controllers may direct pilots to change altitudes for various reasons, such as to maintain safe separation between aircraft, accommodate traffic patterns, or ensure compliance with the established flight levels. This adherence to ATC guidance is essential for safety in crowded skies and can help manage the flow of air traffic more effectively.

While avoiding turbulence, ensuring a smoother flight, or maintaining fuel efficiency may also be valid considerations for altitude changes, they are not the primary reasons under IFR. Safety, regulations, and compliance with ATC directives take precedence in operational decisions. Thus, the correct answer reflects the critical aspect of flying under IFR, which involves strict adherence to instructions and protocols laid out by ATC.