Instrument Approaches

Thanks for all your questions~ Before we starts, these information is more on IFR level; therefore, if you got a bit confused. That's very normal. Just comment below for your questions, and I will shred some light for you~

Lets look into Instrument approach.

In IMC Instrument meteorological condition, Instrument approaches is an aid to guide the aircraft down to Minimum; then, pilot will have to visually fly down to the runway.

During IFR training, you will learn some basic IFR procedure; SID/Cruise/STAR/IAP.

We will focus on IAP on this post. Instrument Approach Procedure can breakdown to two main categories: Precision Approach and Non-Precision Approach.

Precision Approach(PA) is an instrument approach and landing using precision lateral and vertical guidance. In contrast, a non-precision approach(NPA) procedure only provides horizontal guidance. (Also, there is Approach with vertical guidance APV.)

The most common Precision Approach is ILS Instrument Landing System.

Usually ILS composed with 4 parts: Localizer (lateral guidance) , Glideslope(Vertical Guidance), Marker Beacon(distance measure) and minimum. A lot of approaches has replaced Marker Beacon with DME. In general, DME provide more accurate distance information. Besides, MLS and GLS also consider Precision approaches as they both provide Precise vertical guidance.

And Non-precision is same as Precision without vertical guidance. (LOC, VOR, NDB, RNAV...) That's why most of the ILS approach will also have a LOC minimum. (Blue highlighted area)

As the GPS technology is advancing, it can maintain its accuracy not only lateral, but also able to provide vertical guidance. However, it is not consider a very precise vertical guidance; therefore, it is consider as Approach with Vertical guidance.

Q)Why Precision Approach?

The precision approach can ensure the aircraft descend along the glide precisely; therefore, Precision approach is approved for a 200ft AAL minimum (CAT1)

Q)What is IAF/IF/FAF? Is it a must to overfly all of them?

IAF Initial Approach Fix, the starting point of the approach. Usually the STAR will transition and lead to IAF. And it is the starting point of the Initial Approach Segment and lead to the Intermediate approach segment.

IF Intermediate Fix. Initial approach segment ends at Intermediate fix, and it begins the Intermediate segment and lead to Final approach segment.

FAF Final Approach Fix. The end of Intermediate fix and start of Final Approach segment, Final Approach Fix is where the glideslope intercepts the glideslope-intercept altitude on Precision Approach. During Non-precision approach, FAF is the starting point where aircraft establish to the final approach course, and it will depicted as Maltese cross.

Normally, we will enter join the approach Via STAR thru the IAF; however, if traffic permitting, ATC might clear for an early intercept of the final approach course. In that case, overflying IAF and IF is not required; however, overflying FAF is a must. (consider Initial approach segment and intermediate segment is the fore-play; the Final approach segment is the real thing!😈)

Checking your understanding, Where is the FAF on the Chart above? Whats the minimum altitude.

Q)Is it required to have OM/MM/IM for ILS approach?

Aforementioned, we need a distance measuring equipment for our approach. In the old days when DME is not commonly available, Marker Beacon is used to locate the Fixes. OM Outer Market to identify FAF; MM middle marker to identify overflying the minimum/MAPt for CAT 1 approach. (decision is required! runway in sight? continue? go around?) Inner Marker IM is usually placed over the threshold, the expected DH for Low Vis operation.

But since DME is more and more common, marker beacon is slowly phrasing out.

Q)On non precision approach, how to gauge the vertical profile?

On non precision approach, if DME equipped, you can follow the DME/ALT table to gauge the vertical profile; if DME is not available, based on the ground speed, you can time the descend from passing FAF to Missed Approach Point MAP. E.g. Given your Ground speed at 100kt; you passed the FAF now, with maintain roughly 540ft/min descend, you will be at MAP in 4mins 11 sec. If runway not insight, missed approach is Manditory.

BTW, side question! From the picture below, Do you have any idea whats this? And how to use it?

Q)How to commence a NPA while using FPA? will it descent like an ILS?

Well, in order to understand that, we need to understand the BIRD (Track/FPA).

Normally, we operate the aircraft via HDG/ VS (and Manage Nav, but simplify the explanation, I will compare HDG/VS and Track/FPA.

HDG/VS is very simple and straight forward (if you have problem understand that, I m sorry that I can help~); however, when selected TRK/FPA, the aircraft will maintain the selected Track; regardless the wind and drift angle, it will maintain same track. Same apply to FPA; once selected FPA is engaged, the aircraft will follow the selected flight path angle, regardless the up and downdrafts. It will descent at the same angle.

That's very helpful when commencing a non-precision approach.

Because there will be the same descend angle (usually 3⁰ descend) from FAF to touchdown zone. Therefore, once you establish the proper descend angle over the FAF, you shall reach to minimum as scheduled distance. Of course, during the descend, you will need to crosscheck the DME/Alt table for discrepancy and do SMALL correction.

E.g. On the RPLL ILS 06 chart above; once you commenced and established 3⁰ descend over the D7.8IML(FAF), you shall able to follow the proper descend angle/path, and reach 380ft MSL at 1.1nm IML.

If not runway in sight til D0.8 IML (MAPt), Missed approach procedure is Mandatory.

It shall have a similar descent path like an ILS; but ILS follows the Glideslope signal and provide guidance. FPA is only a tools to help constant descend angle, which will not provide any guidance.

Q)When G/S inop, ILS can downgraded to LOC app, what if LOC inop?

Well~That's a good question! It brings up to another question.

Can we descend on Glideslope without establish on LOC? Comment what you think! I will answer this question later!

Q)Turboprop and Jet characteristic during App?

Of course, the handling and configuration is a bit different; but in terms of Instrument approaches, the biggest different would be their Target Approach Speed.

Turboprop is usually consider Category B based on it Approach speed. Jet usually has a higher approach speed and higher weight. In case of go-around at minimum, due to its speed and weight, it has a higher momentum; and it requires more time to react before positive climb. That's why in some airports, there is different minimum or visibility requirement for different App Categories.

Q)What's DME arc? and how to commence an DME arc?

Some approach require DME arc to lead the aircraft to FAF. Simply fly and maintain certain DME thru an arc to Final approach course. For commencing, I will start another post for detail discussion on DME arc.

Q)Why only 3 entries in Holding?

There is 3 entries for holding. ( Direct, Parallel and Teardrop)

It is because these 3 entries covered the whole 360⁰; regardless what radial ATC ask you to hold on.

I have opened a new discussion about Holding pattern.

Go ahead unload all your questions about holdings there~

Q) LDA, circle to land and procedure turn

A localizer type directional aid (LDA) or Instrument Guidance System (IGS) is a type of localizer-based instrument approach to an airport. It is used in places where, due to terrain and other factors, the localizer antenna array is not aligned with the runway it serves. Circle to land usually seen in terrain surrounded airports. Instrument approach is only available from one side. Therefore, when wind is favorable on the other side; pilots might required to commence instrument approach from one side, and visually circle to land on the other side of the runway.

Procedure turn is simply a U turn by commencing a teardrop entry. Fly outbound 45⁰ for 1 minutes then 180⁰ turn and re-intercept the course.

Q)Airbus CAT3 Single vs CAT3 Dual? What are the difference?

In Airbus terms, CAT3 Dual means Fail operational CAT3 Single means Fail Passive.

Lets discuss in depth in Low Vis post~ Don't wanna confuse other guys here~lol

Q)EOSID vs EOSTAR?

When Engine out, the aircraft might not able to maintain the required climb gradient for the SID; so Engine out SID needed; it is a Pre-planned departure for limited climb performance to stay clear of obstacles. ( it varies on companies and airports.)

However, I have never heard a EOSTAR. ( let me know if you come across 1, I would like to learn about it!) In case of EO, you would not want to fly into terrain area. If ever, I believe ATC shall Radar Vector or direct you to certain fix to avoid terrain. When flying over terrain area during cruise, we shall review the company establish escape route. In case Engine flameout, we will be ready to follow the established route to divert (and avoid the terrain, EVEN IF the alternate airport is farther away.)

Got more questions about Instrument Approaches?? Comment below!!

if you have any thots or doubt, feel free to comment below~ I will reply on your answer~