Approach Types

Tizi
Apr 18
7 min read

Updated: May 9

"I shall follow the glideslope to the DA" - IFR student shooting a VOR approach.

To simplify the scrolling back and forth, this is the table of contents for this article.

Ground-Based Navigation Approaches
1. Very High Frequency Omnidirectional Range (VOR)
2. Localizer (LOC)
3. Instrument Landing System (ILS)
RNAV (GPS) - Based Navigation Approaches
1. Localizer Performance with Vertical Guidance (LPV)
  1. Widea Area Augmentation System (WAAS)
2. Localizer Performance
3. Lateral and Vertical Navigation (LNAV/VNAV)
4. Lateral Navigation (LNAV)
5. Advisory Vertical Guidance (+V)
GRAPHIC - Summary of Most Common Approaches
Less Common Approaches
1. RNAV (RNP) AR
2. Ground Based Augmentation System (GBAS) Landing System (GLS)
3. Localizer Type Directional Aid (LDA)
4. Simplified Directional Facility (SDF)

Ground-Based Navigation Approaches

The most traditional forms of approach use ground-based navigation sources. These are physical systems located on the ground across the United States: Very high frequency Omnidirectional Range (VOR), Localizers (LOC), and Instrument Landing Systems (ILS). There are a few more like NDB and various localizer types.

In Garmin-world, we describe these as "green needle" approaches, because the CDI changes color to green when choosing 'VLOC' (VOR / LOC) as a navigation source.

These are physical stations located on teh ground. The aircraft must be equipped with appropriate antennas and interfaces to tune into the station and receive information. For example, to tune to a VOR, you must have a VOR receiver antenna and a navigator to select the desired frequency.

With the advent of GPS, ground-based navigation equipment has been coming realtively obsolete. That doesn't mean it's not relevant (far from that, actually). However, since they are physical equipment, they require a lot of maintenance. If they brake, staff needs to be dispatched. If someone drives into the station with their car, staff needs to be dispatched to fix it. Get it? As such, more and more of these have been decommissioned. Nevertheless, the United States Government recognizes that relying solely on GPS-based navigation is risky, as an incapacitation of the satellite system would result in aircraft not being able ot navigate or land safely. As such, the FAA has established the Minimum Operational Network (MON), a series of ground-based navigation sources that will always be maintained. Airports that are served by the MON are labeled above the airport name on the IFR chart, as shown below.

Very High Frequency Omnidirectional Range (VOR)

The most basic approach using ground-based navigation sources is the VOR. I won't cover how VORs work in this article (read the article "VOR for Idiots" instead). VOR approaches are non-precision approaches with a Minimum Descent Altitude (MDA). This is an altitude below which an aircraft may not descend without having visual of the runway environment. The approach can be flown to the missed approach point (MAP) before the aircraft must execute the missed approach (i.e., the approach failed, the runway cannot be seen).

The VORs must be tuned into your navigation radio "NAV" and properly identified. You tune the various radials based on the specific approach plate.

The VOR approaches provide linear lateral guidance only. What I mean by lateral is that it does not offer any vertical guidance. The lateral guidance is not particularly precise. In fact, we call it linear guidance. The precision of the guidance does not change as you get closer to the runway. What do I mean by this? Imagine you are 5 NM out on a VOR course towards the runway. If your course deviation indicator (CDI) is fully deflected to one side, you are off-course by 10 degrees (off the tuned radial). If you maintain that deviation all the way to the missed approach point (MAP), you will still be 10 degrees of course. See the image below for reference. The two dots on the approach path represent the CDI deviation dots.

VOR approaches could be considered "old school". They are notoriously more difficult to fly, require more workload, and are dependent on a finely tuned VOR station (i.e., well maintained). You should also know that VORs can be imprecise and a bit iffy. Not the big ones like SAV, but the smaller ones that rely on local maintenance. To this effect, the FAA allows pilots to fly VOR approaches using GPS, as long as you are monitoring the VOR in some fashion (a secondary CDI or a bearing pointer will do just fine... I prefer the bearing pointer...).

You may notice that the VOR will often be the Initial Approach Fix (IAF) to the approach. That is because they belong to the traditional network of VORs and Victor airways. If you only had VOR navigation, you need a way to commence the approach from the enroute world (composed of VORs and Victor airways). For example, here is Savannah International (KSAV) VOR/DME-A approach (circling only).

Note how the SAV VORTAC is at the center of a vast network of airways (left): V3, V437, V441, V37, etc.). On the plate, the VOR is labeled 'IAF'. In this case, the IAF leads you to a simple procedure turn to capture the Final Approach Course (FAC) of 024 degrees.

Because there is no vertical guidance, it is the pilot's responsibility to descend respecting all the stepdown altitudes. Depending on the complexity of the approach, there could be few or many. There are two philosophies on descending to minimums on non-precision approaches without vertical guidance:

Stabilized Descent. This procedure uncourageous pilots to establish a stable continuous descent, verifying that all altitudes are respected. A drawback is that you may not break out of the clouds as soon as you may want.
Dive and Drive. This proceure involves descending as quickly as possible to the stepdown altitudes - dive - and leveling off until the next one is sequenced - drive. The point is to go as low as you can as quickly as you can in hopes of going visual. I need to emphasize that certain approaches require you to "dive and drive" to offer the pilot the opportunity to see the runway environment prior to the MAP and be in a position to land.

VOR approaches may require an extensive manipulation of courses, increasing pilot workload. Just like any other approach, they can also be flown vectors-to-final (VTF) with Air Traffic Control (ATC) support. Because of their imprecise nature - like the linear guidance - you can expect the MDA to be relatively high.

Localizer (LOC)

Localizer approaches are non-precision approaches with an MDA. Just like VOR approaches, the localizers are for lateral guidance only. The localizer antenna is traditionally located at the very end of the runway (departure end) and you need to tune the localizer frequency into your NAV and tune the appropriate course (radial). However, differently from VOR approaches, the guidance is very precise and gets better as you fly closer to the antenna. We call it angular guidance. The precision of the guidance changes as you get closer to the runway. What do I mean by this? Imagine you are 5 NM out on a VOR course towards the runway. If your course deviation indicator (CDI) is fully deflected to one side, you are off-course by X feet. If you maintain that deviation all the way to the missed approach point, you will will be a lot less than X feet off the course. See the image below for reference. The two dots on the approach path represent the CDI deviation dots.

Localizers also are relatively workload intensive. Depending on how you approach the IAF, you may need to transition from GPS to LOC (change navigation source) at the right time. Because localizers are a component of the instrument landing system (ILS) (see section below), LOC approaches are often combined with ILS plates: 'ILS or LOC RWY 10'. There are however cases where these are standalone procedures. The most famous is probably the one in Aspen, CO (KASE), where both the approach and the missed approach are composed of localizers (two, in fact!):

Just like the VOR approaches, localizers are flown vertically at the user's discretion, as long as the stepdown altitudes are respected. In the case of this approach, there are plenty of stepdown fixes and altitudes:

KASE Localizer Vertical Profile

Instrument Landing System (ILS)

The Instrument Landing System (ILS) approach is the only ICAO recognized precision approach with a Decision Altitude (DA). A decision altitude, or "DA", is an atltitude at which, on your descent, you must decide whether to continue to landing or execute the missed approach. This DA has a safety margin allowing you to descent slightly below it while you make the decision. Note that the DA becomes your missed approach point, since you are following vertical guidance down to the runway.

The ILS provides angular guidance both laterally and vertically by virtue of two separate antennas: the localizer (laterally) and the glide slope (vertically). The localizer is the same localizer used for the "localizer approaches" (see previous header).

ILS lateral (LOC) and vertical (GS) guidance

Because the ILS is composed of two antennas, you will very often see the ILS approach provide also localizer only minimums. The title may in fact say "ILS or LOC". This article talks about regulations concerning inoperative glideslopes, and how an ILS approach becomes a LOC approach.

Just like any approach with vertical guidance,

RNAV (GPS)-Based Navigation Approaches

With the advent of GPS, ground-based navigation equipment has been coming relatively obsolete. That doesn't mean it's not relevant (far from that, actually, did you read about the MON, above?).

GPS approaches are built "in space" based on GPS-altitude (GALT). They are referenced to Barometric altitude, but they are flown following guidance "floating in space".

In Garmin-world, we describe these as "magenta needle" approaches, because the CDI changes color to magenta when choosing 'GPS' (LNAV, LP, etc.) as a navigation source.

There are many lines of minima available for RNAV (GPS) approaches.