2.3.12 ATC-Assignment of Levels and Altitudes Levels shall be assigned/reported as follows • For altitudes the word FEET shall follow the level indication. The word ALTITUDE may precede the level indication. • For flight levels, the level indication shall be preceded by the term FLIGHT LEVEL
Use of the Terms To and For According to ICAO PANS-ATM a level assignment may be given as follows:
Altitude ABC 123 CLIMB TO 5000 FEET Flight Level ABC 123 CLIMB TO FLIGHT LEVEL 150
However several countries have banned the use of the words TO and FOR in connection with the assignment / report of levels due to the risk of confusion with the corresponding numbers TWO and FOUR. In the following chapters the official ICAO wording is used. For further information on country specific RT phraseology please refer to the appropriate CRAR.