91.239 Altimeter settings

• (a) A pilot of an aircraft must maintain the cruising altitude or flight level of the aircraft by reference to an altimeter that is set in accordance with the following:
  • (1) when operating at or above flight level 150, set altimeter to 1013.2 hPa:
  • (2) when operating at or below 13 000 feet, set altimeter to the appropriate area QNH zone setting or aerodrome QNH altimeter setting:
  • (3) when operating between 13 000 feet and flight level 150, set altimeter to the appropriate area QNH zone setting as advised by an ATC unit.
• (b) A pilot of an aircraft that is ascending or descending must set the altimeter in accordance with the following:
  • (1) when ascending above 13 000 feet, set altimeter to 1013.2 hPa:
  • (2) when descending through flight level 150, set altimeter to the appropriate area QNH zone setting or aerodrome QNH altimeter setting.