The transition level is the lowest flight level above the transition altitude. I believe on the SVMI chart with a published Trans Alt: of 12'000, you would set your altimeter to 1013mb/29.92Hg upon reaching 12'000' indicated. Depending upon company SOP, the standby altimeter might also be changed at the transition altitude/level or at top of climb/top of descent. In most modern aircraft, not doing so will result in some form of an altimeter missmatch error. Keep in mind that, in reality, the transition level 'floats' based on the QNH - the lower the QNH, the higher the transition level - If the QNH is low and the pilots wait until approaching FL180 to change the altimeter subscale, an Level Bust is possible.Д«oth primary altimeters are changed at the same time. If the cleared level is FL180, an early change is prudent.Дescending, even when cleared to an altitude at the time cruising level is vacated, the altimeters will remain on standard pressure until just prior to the transition level. In practice, this will see the pilots changing to QNE (depending upon the altimeter subscale) as they climb through 18000 feet.

Guidance on changing barometric pressure setting:ДЎ.all changes shall be made in the standard pressure region (ie above 18,000 ft) andДў.the change is to take place just after entering or just prior to leaving the standard pressure region. This restriction ensures that a minimum of 1000' vertical separation is maintained between the aircraft at 17000' on QNH and the one at the lowest useable level on Standard Pressure Setting (QNE). If the altimeter setting is lower, the lowest useable FL becomes FL190 or even FL200. Under conditions of QNH at or above 1013 mb, FL180 becomes the lowest useable FL.

In the US and Canada, the transition altitude is fixed at 18000 feet and the airspace above is known as the Standard Pressure Region

The airspace between the transition altitude and the transition level. The lowest flight level available for use above the transition altitude. The altitude at or below which the vertical position of an aircraft is controlled by reference to altitudes.

Latinvfr svmi altitud error