BY ORDER OF THE SECRETARY OF THE AIR FORCE AIR FORCE ...

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AFMAN 11-217V1 3 JANUARY 2005
clearances. The transition layer may be published, or it may be supplied by ATC via the
ATIS or during arrival. Half flight levels may be used: for example, “FL 45.”
18.6.5. Transition Layer. That area between the transition altitude and transition level.
Aircraft are not normally assigned altitudes within the transition layer.
18.6.6. Transition Between Flight Levels and Altitudes. The vertical position of an
aircraft at or below transition altitude shall be expressed in altitude (QNH or QFE as
appropriate). Vertical position at or above the transition level shall be expressed in terms
of flight levels (QNE). When passing through the transition layer, vertical position shall
be expressed in terms of flight levels (QNE) when climbing and in terms of altitudes
(QNH or QFE as appropriate) when descending. After an approach clearance has been
issued and the descent to land is commenced, the vertical positioning of an aircraft above
the transition level may be by reference to altitude (QNH or QFE as appropriate)
provided that level flight above the transition altitude is not indicated or anticipated. This
is intended for turbo jet aircraft where an uninterrupted descent from high altitude is
desired and for airfields equipped to reference altitudes throughout the descent.
18.6.7. Altimeter Errors. The allowable altimeter errors at a ground checkpoint in ICAO
are different than in the US and vary by airport elevation and atmospheric pressure. Use
the following tables to determine allowable altimeter errors. If your aircraft flight
manual is more restrictive than the values shown in these tables, comply with the
guidance in your aircraft flight manual.
Table 18.5. Allowable Altimeter Errors at Ground Checkpoint for Airports Up to 3500
Feet Elevation With Atmospheric Pressure at or Above Standard.
Airport Elevation Atmospheric Pressure Altimeter Range Allowable Difference
3500 Feet or Below At or Above Standard 0-30,000 Feet ±60 Feet
3500 Feet or Below At or Above Standard 0-50,000 Feet ±80 Feet