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HOW TO READ YOUR INSTRUMENT APPROACH CHART LIKE A PRO – PART 1

HOW TO READ YOUR INSTRUMENT APPROACH CHART LIKE A PRO – PART 1

INTRODUCTION

The objective of this tutorial is to teach pilots how to instinctively look at an instrument approach chart with a critical eye.In this lesson, we will attempt to unravel the mysteries of what the chart symbols mean, and what certain small details on the chart that, if not understood or complied with, can lead to significant consequences during an approach. I will refer to these as “gotchyas”.

At times, I will show an approach chart and ask the reader questions about the symbols or procedures on the diagram. The goal is to train the pilot to look closely at the fine details on the chart. Please do not feel bad if you get the answer wrong, since the objective is training, and not testing.

“FLYING” THE INSTRUMENT APPROACH CHART

A secondary part of this tutorial will address how to fly the vertical profile associated with the procedures on the chart. This will be covered in detail since many of my instrument students, even those who are already rated, have difficulty with this subject.

LET THE GAMES BEGIN

Question; There are three significant gotchyas on this approach. What are they?

Answer:  The first gotchya on this approach is that it is not authorized at night. The second one is that the maximum indicate airspeed at which you can legally fly this approach is 90 knots. Note that only Category A is authorized, with Cat B through D shown as NA. And the third one is the steep 4 degree approach angle for the VGSI, or in this case, the VASI.

Recall that approach categories are based on 1.3 x Vso, or the indicated airspeed you choose to fly. If that speed is greater than 1.3 Vso, the minimums for the next higher category must be used. As a review, here are the approach categories and the speeds associated with them;

  • Cat A; less than 91 knots
  • Cat B; 91 to 120 knots
  • Cat C; 121 to 140 knots
  • Cat D; 141 to 166 knots

FLYING THE VERTICAL PROFILE

Now let’s discuss how to fly this approach. Note that there is no vertical guidance available such as LPV or VNAV. There are two ways to fly the vertical profile for this approach. Using the tried and true “dive and drive” method, you cross JILUB at or above 2500 feet, then descend to cross ZOPDU at or above 1800 feet, then descend to the MDA of 1080 feet.

However, if your navigation equipment has WAAS, you will get a reference glide path on your GPS screen which, if followed, will result in a descent angle of approximately 3 degrees, the same as an ILS glideslope.

THE FINE PRINT!

There is a note in the profile box on the approach chart for the GPS RWY 7 at Skymanor that says;

“VGSI and descent angles not coincident (VGSI angle 4.00, TCH 31”.

VGSI means Visual Glide Slope Indicator, which in this case is a PAPI which, for Runway 7 is set for a 4 degree approach angle due to a displaced threshold and trees in the approach path. If the VGSI is followed, will result in a threshold crossing height of 31 feet.

Since the reference glidepath is 3 degrees, versus 4 degrees for the VGSI, once the runway comes in view, you will be below the visual glidepath, and will see all red lights. At this point, the pilot should level off at or above MDA, fly level until established on the VGSI, then follow it to the runway.

The PAPI or VASI always have precedence over the reference glide path at or below MDA or DA. The important point to remember is that reference glide paths do not guarantee obstacle clearance. Never fly the reference glide path below MDA or DA when there is a PAPI, VASI, or any other visual approach indication available.   

TECHNIQUES FOR FLYING THE VERTICAL PROFILE

Here is my technique for flying a glide path or glideslope. If I am at, for example, 3000 feet, and ATC clears me to maintain at or above 2500 feet until established on the final approach course, I stay at the higher altitude until intercepting the glide path, or glide slope. There is no reason to descend to the lower altitude if the clearance is to maintain “at or above”. The sooner the glide path is captured, the sooner you can figure out what power setting will keep you on the glide slope or glide path.

We will now discuss how to fly the ILS approach to Runway 22 at Wilkes-Barre/Scranton, PA using the glide slope.

Assume we are being vectored at 4000 feet when the controller tells us to maintain 4000 feet until established on the final approach course, cleared for the approach.

Question: How would you fly the vertical profile?

Answer: Again, there are two ways to fly the vertical profile for this approach. The easiest and safest way is to simply maintain 4000 feet until established on the localizer, intercept the glide slope, then fly it to the DA of 1201 feet.

The other method is, using the dive and drive technique, cross COSBY at or above 4000 feet, JULUT at or above 3200 feet, WEXIN at 2800 feet, intercept the glideslope, and fly it down to the DA.

Both methods work, but the dive and drive technique increases pilot work load, while unnecessarily introducing the possibility of an altitude bust.

Question: What is the significance of the fix XAGKE, and how will it affect you on the approach?

Answer: XAGKE is a stepdown fix, and it only applies if you are flying a localizer only approach, without any form of vertical guidance. Without any form of vertical guidance, you will be required to use the dive and drive method to cross XAGKE at 1740 feet before descending to the MDA. However, if flying the full ILS, the 1740-foot crossing restriction will be complied with by staying on the glide slope. Again, it is the pilot’s responsibility to verify that each crossing restriction is met, regardless of which method of descent is used.

To recap, when flying the localizer only approach, with no vertical guidance, the profile should be flown as follows, assuming you will want to be at the minimum crossing altitudes, and not above them;

Cross COSBY at 4000 feet, descend to cross JULUT at 3200 feet, descend to cross WEXIN at 2800 feet, descend to cross XAGKE at 1740 feet, then descend to the MDA of 1420 feet, stay at 1420 feet until reaching the black V on the approach chart (which will be discussed later), then begin a normal descent to the runway.

Note: If the approach does not have a glideslope, or if it is NOTAMed out of service, use your computed glidepath, if available, and simply fly it to the MDA, while checking that all altitude restrictions are met. But keep in mind that computed glide paths are non-precision approaches, and as such, you are still restricted to the MDA shown on the chart. 

Question: When flying this approach using the full ILS with a glideslope, what is the missed approach point?

Answer: It is the Decision Altitude of 1201 feet.

Question: What is the black V at the 1.7-mile fix, and how does it affect you on a full ILS approach?

Answer: The black V is a Visual Descent Point, or VDP, and they do not apply when flying an ILS with a glideslope, an LPV, or a VNAV path. The main function of the VDP is to prevent premature descents from MDA, which may result in getting too low prior to reaching the runway. They are intended to be used when flying without any form of vertical guidance, such as on a localizer only or LNAV approach, and are an aid in maintaining a stabilized approach from the MDA to the runway.

VPDs are designed so that if you cross them at the MDA, then make a normal visual descent to the runway, it will result in a 3 degree approach angle, the same as a glideslope. To use them properly, you must not descend below MDA until reaching the VDP.

As a side note, using a VDP is at the discretion of the pilot, and is not mandatory, but highly recommended. Now let’s have some fun with the RNAV/GPS RWY 5 Approach to the Pocono Mountains Municipal Airport.

Question: Since there are no instrument approaches to Runway 23 at KMPO, we are flying the RNAV/GPS RWY 5 approach and planning to circle to Runway 23. Night, IFR conditions exist with the weather being 900 overcast, 5 miles visibility, with surface winds 230 degrees at 15 knots. Can you spot the gotchya on this approach chart?

Answer: The critical eye will spot the gotchya, which is found in the fine print above the frequency line. While circling minimums exist weather wise, circling to Runway 23 is not authorized at night. Since this is my home airport, I know that just prior to the threshold for Runway 23, there exists rising, and unlighted, terrain and trees.

This example reinforces why instrument pilots simply must study the approach chart carefully, and with a critical eye! Failure to notice the smallest of details can have a significant impact on the safety or legality of the approach.

NOW FOR A LITTLE UNSUPERVISED SOLO

You are flying into the Pocono Mountains Municipal Airport in Day, IFR conditions, and planning a straight in RNAV/GPS approach to Runway 5. While flying level at 5000 feet, and going direct to WIBUM, you receive the following IFR approach clearance:

 “Bug Smasher 524 Hotel Sierra, cross WIBUM at or above 4000 feet, cleared for the RNAV GPS Runway 5 approach.”

Assuming you will be flying the LPV approach, how will you fly the vertical profile? What is the fix at YONUP, and how will it impact your profile?

CONCLUSION

I sincerely hope the information provided in this tutorial has been of use to my esteemed readership.

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