Approaches

The different type of IFR approaches and related information to flying them.

There are two basic kinds of approaches: Precision and Non-Precision. Precision, as the name implies, provide much more accurate navigation. Specifically, they provide more precise lateral and vertical guidance. Precision approaches prescribe a decision altitude or height where the pilot decides to either continue the approach or go missed. Non-precision, on the other hand, prescribe two things: a minimum descent altitude (or height), and a missed approach point. In a non-precision approach, you descend down to the MDA, then hold at or above that altitude until you either have everything needed to continue the approach, or you reach the missed approach point. If you reach the missed approach point, and are unable to continue the approach, you must execute the missed approach procedure.

Descending below MDA/DA

Part 91.175.

You can descend below the MDA/DA when all of the following conditions are true:

  • The aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers. i.e. no chop and drop/slipping.
  • The flight visibility is not less than the visibility prescribed in the standard instrument approach being used.
  • At least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:
    • The approach light system, except that the pilot may not descend below 100 feet above the touchdown zone elevation using the approach lights as a reference unless the red terminating bars or the red side row bars are also distinctly visible and identifiable.
    • The threshold.
    • The threshold markings.
    • The threshold lights.
    • The runway end identifier lights.
    • The visual glideslope indicator.
    • The touchdown zone or touchdown zone markings.
    • The touchdown zone lights.
    • The runway or runway markings.
    • The runway lights.

Approach Category

See AIM 5-4-7 (e).

The approach category for the aircraft is defined by the approach speed - VREF. Though, if you decide to fly the approach at a higher speed than VREF, then you must use the minimums specified for the category containing the speed you’re flying at (e.g. if you’re in a plane that with a VREF of 85 kts, but decide to fly the approach at 95 kts, then you must use the minimums defined for Category B).

Category ACategory BCategory CCategory DCategory E
Speed (kts)0 to 9091 to 120121 to 140141 to 165165 or greater

Circling

See AIM 5-4-20.

Circling is a maneuver conducted after an approach, but is not a type of approach itself. Circling is performed whenever the final approach course is not aligned with the runway (within 30°), when landing on a different runway from the approach flown, or when the runway is not specified in the approach (e.g. flying a VOR-A).

Circling may be done if the winds do not favor the runway the chosen approach is for - e.g. if winds favor runway 15, but the approach is for runway 25, then you might fly the approach for runway 25, circle to land runway 15.

See this article from CFI Notebook on circling.

Circling Minimums

Published minimums provide at least a 300 foot obstacle clearance when you remain within the appropriate area of protection. Remember to descend to the circling MDA/DA, not the straight-in MDA.

If no circling minimums are published, circling requires ATC authorization and at basic VFR (at least 1000 ft ceiling with visibility 3+ statute miles).

Remain at or above the circling MDA altitude until the aircraft is “continuously in a position from which a descent to a landing on the intended runway can be made using normal maneuvers”. This is typically just inside the 180. Abeam for most circling minimums would have you low on downwind.

Circling Radius

Depending on the approach category (speed you fly at), you have different circling radius - the minimum distance you must remain from the runway while circling to land.

Demonstration of the circling radius.

Standard Circling Radius

Circling approach protected areas developed prior to late 2012 use the radius distances shown below.

Circling MDACAT ACAT BCAT CCAT DCAT E
All altitudes1.3 NM1.5 NM1.7 NM2.3 NM4.5 NM

Expanded Circling Radius

Per the AIM, Circling approach protected areas developed after late 2012 use the radius distance shown below.

Circling MDA (feet MSL)CAT ACAT BCAT CCAT DCAT E
1000 or less1.3 NM1.7 NM2.7 NM3.6 NM4.5 NM
1001 to 30001.3 NM1.8 NM2.8 NM3.7 NM4.6 NM
3001 to 50001.3 NM1.8 NM2.9 NM3.8 NM4.8 NM
5001 to 70001.3 NM1.9 NM3.0 NM4.0 NM5.0 NM
7001 to 90001.4 NM2.0 NM3.2 NM4.2 NM5.3 NM
9001 and above1.4 NM2.1 NM3.3 NM4.4 NM5.5 NM

Missed Approaches

Most instrument approach procedures also have a missed procedure. These are described in the top-left box of the approach plate, and then visually depicted as part of the top-down view.

If you choose to, must, or are instructed to go missed, you follow those instructions. If you were not on the final approach course (that is, if you were circling to land), then you get back on the final approach course as part of going missed.

See this article from AOPA on going missed.

See this article from BoldMethod on going missed below the MDA/DA

PT - Procedure Turn

Depicted as a line with a barb from a course in an approach plate. The barb indicates the direction to turn. Procedure turns are maneuvers enable the following:

  • course reversal
  • descent from an IAF
  • Inbound course interception.

Procedure turns or hold-in-lieu-of-PTs are mandatory whenever they are depicted on the approach plate. However, they are not permitted when:

  • “NoPT” is depicted on the plate
  • Radar vectors to final
  • Conducting a timed approach from a holding fix.

The maximum speed when performing a procedure turn is 200 kts IAS. You must remain within the charted distance (usually 10 NM), and comply with published altitudes for obstacle clearance.

The shape of the maneuver is mandatory if a teardrop or hold-in-lieu-of-PT is published. Otherwise, only the direction.

A teardrop procedure may be be published instead of a procedure turn.

Do not perform a procedure turn when SHARPTT:

  • Straight-in approach clearance
  • Holding in lieu of a procedure turn
  • DME Arc
  • Radar vectors to final
  • NoPT shown on chart
  • Timed approach from a holding fix
  • Teardrop course reversal.

ILS - Instrument Landing System

the ILS is composed of two main parts: the localizer and the glide slope. In addition, there are marker beacons at specific locations.

The ILS is described mostly in AIM 1-1-9.

Localizer

The localizer is essentially a more-sensitive VOR that broadcasts a single radial. It’s located inline with the runway, behind the runway. It broadcasts 2 signals - one at 90 Hz, the other at 150 Hz. The intersection of the signals is aligned with the extended runway centerline, and the receiver on the airplane can interpret these to show how off course the airplane is.

boldmethod.com on the localizer signal

The width of it is between 3° and 6° - such that the width at the runway threshold is 700 feet. Usually, it’s a 5° total width (2.5° full deflection on each side, or 4 times more sensitive than a VOR). The coverage range is a 35° on each side of the centerline up to 10 NM. After that, out to 18 NM, with 10° each side of the centerline. It goes out to an altitude of 4500 feet.

boldmethod.com on the localizer service volume

Glide Slope

The glide slope provides vertical course guidance. The transmitter is located off to the side of the runway (about 250-650 away from the runway centerline), between 750 and 1,250 feet behind the runway threshold.

Similar to the localizer, the glide slope broadcasts 2 signals, at 90 and 150 Hz, with the intersection of them providing a - usually - 3° glide slope down to the runway.

A glide slope has a width of 1.4° (0.7° on either side), with a range out to 10 NM. As previously stated, it provides a 3° slope, unless otherwise charted.

⚠️ Due to, literally how physics works, there’s a false glide slope significantly above the normal glide slope.

boldmethod.com on the glideslope signal

Marker Beacons

Marker beacons provide range information over specific points on the approach. There are 3 that are part of an ILS, named the outer marker, middle marker, and inner marker. There also exists the back course marker, but that’s not part of the ILS approach.

Marker TypeLocationColorSignal
Outer Marker4-7 NM out. Approximately where the aircraft should intercept the glide slope.BlueDashes “- - -”
Middle Marker~3500 feet from the runway & 200 feet above the touchdown zone elevation. Where the glide slope meets the decision height.Amber“· - · -”
Inner MarkerBetween the middle marker and the runway threshold. Indicates where the glide slope meets the decision height on a CAT II ILS approach.WhiteAll dots. “· · · ·”
Back CourseThe final approach fix on “selected back course approaches”, not a part of the ILS approach.Whitetwo-dots “·· ··”

ALS - Approach Light Systems

See AIM 2-1-1.

  • Provides basic visible means to transition between instrument-guided flight into a visual approach.
  • The ALS extends from the landing threshold into the approach area up to:
    • 2,400 to 3,000 feet for precision instrument runways, and
    • 1,400 to 1,500 feet for non-precision instrument runways.
  • May include sequenced flashing lights, which appear to the pilot as a ball of light traveling towards the runway at 2 times a second.
  • The visible parts of the ALS configuration can help the pilot estimate flight visibility.

ILS Minimums

See this chart:

CategoryVisibilityDecision Height
CAT I2,400 feet or 1,800 feet200 feet
CAT II1,200 feet100 feet
CAT IIIa> 700 feet< 100 feet or no decision height
CAT IIIb150 to 700 feet< 50 feet or no decision height
CAT IIIc0 feetNo decision height

Last updated: 2021-05-27 22:36:50 -0700