What should a pilot set the altimeter to when operating between 13000 feet and flight level 150?

When operating between 13,000 feet and flight level 150, the pilot should set the altimeter to QNH given by ATC, which is the correct choice. This is because QNH represents the atmospheric pressure at sea level, allowing the pilot to maintain accurate altitude readings in relation to the true vertical position above sea level. Setting the altimeter to QNH as directed by ATC ensures that all aircraft in the airspace are operating under a consistent reference, which is crucial for maintaining vertical separation and safety among various aircraft.

In this altitude range, it is standard practice to utilize the QNH provided by air traffic control rather than standard pressure settings, which can lead to inaccurate altitude indications that could affect flight safety. At flight levels, pilots generally switch to the standard altimeter setting of 1013.2 hPa (hectopascals) when transitioning above flight level 180. However, since this question specifically pertains to the altitude range before reaching flight levels, the appropriate choice is to use the QNH.

Other options, such as 1013.2, regional QNH, or QFF, do not provide the same level of specificity or coordination as the QNH given by ATC for the particular airspace