by Jonathan M. Stern
The profile view depicts the approach from the side and provides all altitudes to be flown along segments of the approach, the distance within which the procedure turn must be completed, the distance from various points to the runway threshold, and other information. Minimum altitudes are indicated by underlining; maximum altitudes are indicated by overlining; and a combination of underlining and overlining indicates that an altitude is mandatory. An altitude with no underlining or overlining is a recommended altitude.
The profile view shows the distance within which the course reversal must be completed and the facility on which the distance is based. Upon completion of the course reversal on an ILS approach, the aircraft may be descended to the glideslope intercept altitude. That altitude is then maintained until the glideslope is intercepted. The profile view depicts the altitude that the airplane should be at when passing the LOM on glideslope.
The profile view on an ILS approach shows a threshold crossing height (TCH). The TCH is, as the name suggests, the altitude at which the aircraft crosses the runway threshold if it is on the glideslope.
Step-down fixes may also be depicted on a profile view. A step-down fix allows a pilot who can identify the fix to descend to a lower altitude. When the step-down fix cannot be identified, the previous minimum altitude applies.