Transition Level

The Transition Level is the lowest available flight level above the transition altitude. At and above the transition level, the altimeter is set to the standard pressure setting of 1013.25 hPa (29.92 inHg), and altitude is expressed as a flight level (e.g., FL180).

• Transition Altitude: The altitude below which the altimeter is set to QNH (local pressure). Pilots set standard pressure (1013.25 hPa) when climbing through transition altitude
• Transition Layer: The airspace between transition altitude and transition level — aircraft should not level off in this layer
• Transition altitude varies by country: 18,000 ft in the US, 5,000 ft in the UK, 7,000 ft in Germany
• Transition level changes with atmospheric pressure and is published in the ATIS
• Ensuring correct altimeter setting prevents altitude errors and separation violations