As you review AIM 5-4-5, note especially the following points:
- The procedure title and notes identify the navigation equipment required to join and fly an instrument approach procedure (IAP).
- If the IAP is aligned with the runway (“straight-in”), it is identified by the navigational system that provides final approach guidance and the number of the runway (e.g., VOR RWY 13).
- If the IAP provides only circling minimums, it is identified by the navigational system that provides final approach guidance and a letter (e.g., VOR A).
- If the IAP requires more than one type of equipment, the title includes a slash (e.g., VOR/DME RWY 31).
- The word “or” indicates that either type of equipment may be used (e.g., VOR or GPS RWY 15).
- WAAS (LPV, LNAV/VNAV and LNAV), and GPS (LNAV) approach procedures are charted as RNAV (GPS) RWY (Number) (e.g., RNAV (GPS) RWY 21).
The instrument approach clearance provides guidance to a position from which you can execute the approach, and clears you to fly that approach. Unless there is only one published instrument approach procedure for the airport or runway to be used, the approach clearance will include the name of the approach (e.g., "cleared for the RNAV(GPS) 17 approach."
Approach minimums are based on the local altimeter setting for the airport, unless otherwise shown on the instrument approach procedure chart. Adherence to the route (course), weather minimums, and altitudes (including published approach minimums) is critical to safe operation in IMC.
For approaches with vertical guidance (i.e., some form of electronic glideslope), approach minimums are expressed as a decision altitude (DA), which is the MSL altitude at which the pilot must start a missed approach if the required visual references are not in sight. For approaches with lateral guidance only (i.e., no vertical guidance), approach minimums are expressed in terms of minimum descent altitude (MDA). MDA, also referenced to MSL, is the lowest altitude to which descent is authorized on final approach or a circle-to-land approach without having the required visual references in sight.
Remember that approach minimums are published for different aircraft categories, as described in
AIM 5-4-20.
According to
14 CFR 91.175, you may not operate below MDA or continue an approach below DA unless the aircraft is continuously in a position to descend to landing on the intended runway with normal maneuvers and at a normal rate of descent, and you have the required flight visibility for the instrument approach procedure you are flying.
You must also have one of the following visual references for the intended runway:
- Approach light system*
- Threshold, threshold markings, or threshold lights
- Runway end identifier lights
- VASI or PAPI
- Touchdown zone, touchdown zone markings, or touchdown zone lights
- Runway, runway markings, or runway lights
* You cannot descend below 100 feet above TDZE using ALS unless the red terminating bars or the red side row bars are visible and identifiable.
