How do I read an IAP (Instrument Approach Procedure)?!?
First off, what is an IAP? An IAP in the simplest terms is what allows a pilot to get from point A to point B if he/she were to go NORDO (no radios). There are two types of instrument approaches, you have your Non-Precision (NDB, ARA, LNAV, VOR, LOC, TACAN, etc.) and then you have your Precision (PAR’s, ILS, LNAV/VNAV, MMLS, etc.). The difference in between these approaches are what’s given to you as you follow them to the runway. Are you provided only left/right guidance? Are you only provided a bearing and distance? Are you provided all of these aides? A precision approach is an instrument approach and landing using precision lateral and vertical guidance with minima as determined by the category of operation. A Non-Precision approach, is normally missing the vertical guidance.
So now that we’ve gotten the basic of what an IAP is, let’s look at how we read a chart. Here below, I have attached an ILS (precision) or LOC (non-precision) for RWY 8R at Hartsfield-Jackson Atlanta International (KATL). Each colored number and associated highlighted section will represent the section of the chart I am discussing.
So first up:
Always ensure you are looking at the correct chart. You will 99% of the time, on all products worldwide, find the approach, runway and airport in the top right hand corner.
This area is known as the Pilot Briefing Area. In this area, the pilot will be supplied with standard information such as frequencies they will encounter while flying this portion, the ATIS frequency, trouble T or no trouble T, inop lighting minima increases, circling restrictions, approach lighting system serving that approach and missed approach instructions.
This area, is called the Planview Area. This is the entirety of the approach as if you were looking down from on top of it. Let’s break this area down and discuss what most items mean.
3A. This is your Final Approach Course, most all Approaches will start with an IAF (Initial Approach Fix), which in this instance is GPEAT and end with a MAP, which in this is not located on the planview. At each way point you will get a name and RADIAL/DME from the course facility. In this case, it is the ILS serving 8R which is named I-ATL. So when you reach GPEAT, you will be 22.8NM from the naviad. You also be givin the final approach course, which is always published whole. In this case you see the final course being 095°. Now if we follow the course from GPEAT to the IF(Intermediate Fix) PEARI, we are given additional information. If you look that the course, 095°, you will see 5000 above that and (7.4) below it. The 5000 is the minimum decent altitude for that segment, you shall not descend below 5000ft until you reach PEARI. The (7.4) is the distance between each fix. So passing GPEAT, you will be 22.8 miles from the ILS system, descending no lower than 5000ft MSL and are 7.4 miles from PEARI. You will continue to follow those instructions all the way in.
3B. These are navaid facility identifiers. The will give you the navaid name, frequency and ident. Each type of navaid has its own symbol depiction. In the center of the airport, we have the ATL VORTAC, to the North East we have the PeachTree VOR/DME and near the center we have the FLANC, a compass locator at Outer Marker.
3C. This is the MSA for the area. MSA stands for Minimum Safe Altitude. Most MSA’s are a 25 NM range and can be broken up into different sectors allowing for different altitudes… if your have a mountain range to the north, but primarily flat low ground everywhere else, it allows you to set the northern MSA to allow for the mountains and set other areas lower. Since ATL is flat, we have a 3100ft MSL MSA in a complete 360° around the ARP, Airport Reference Point, which is the center of the airport.
This is simple an airport diagram.
This is the PROFILE view, drawn like you are standing next to the approach. It provides the pilot with the some of the same information as the plan view. On the profile view, you are also given the GS, which on this approach is 3.00° and the TCH (Threshold Crossing Height) of 53ft.
5A. Something to note about this approach, is this sentence right here. This is not uncommon to see. VGSI is another acronym for the PAPI’s. So what this is telling you is the lights on the ground, do not equal the same path as taking the GS/GP. Sometimes these differences are less than 0.01° difference and you wouldn’t notice, but we are required to place that note.
- Last, but not least, the minima’s table. Now, depending on where you are from, you will see either FEET or METERS when pertaining to visibility. In the United States it is done in feet. So lets dig right in to the S-ILS 8R: the first number up is what is called the DA (decision altitude), it is 1278ft MSL, it is at this point the pilot must decide “im going for it johnny!” or “ive not got the sack today….”, but in all seriousness, whether the pilot can continue, depends on a few things. The most important thing is, at that point, can he/she see the landing environment, be it the runway or approach lighting. He can you say?! Great news, he may continue the approach, He cant…. Well off to the TROY holding pattern.
If you look back at 5, just past the * youll see what looks to be a bolded V. That is called the Visual Descent Point, this is a point where the pilot may actually now, take over the approach visually if the conditions are met. The next number, 40 is the prevailing visibility/RVR required (RVR in hundreds of feet), so the pilot in this case, needs 4000ft RVR. Moving onto the next number, 254… this number will always differ on the type of the approach. This number represents the distance the pilot is from the ground at the DA/DH and or MDA based on an approach. When it is an ILS approach the number is based on the the touch down zone elevation. So for the ILS 8R (HAT), we take the DA (1278ft) and subtract the TDZE (1024ft) and we get 254ft. For the Localizer (HATh), you would take the MDA (1440ft) and subtract the the TDZE (1024ft) and we get 416ft. Some airports may not provide a TDZE and in which that case they should provide the height above threshold (HATh) in which you would use. For a circling approach, which is not authorized in this case, you would use the HAA (Height Above Airport) which would be the APT ELV. Moving onto the numbers in the parenthesis, we have our ceiling and prevailing visibility requirements. So the weather must be reporting a 500ft AGL ceiling at a minimum and visibility of at least ¾ mi prevailing. If this were a plate out of Europe, the RVR and visibility would be issued in meters.
O! and one last thing I forgot to explain, in area 6 is CATERGORY, that is the category that your aircraft falls under, you then follow that set of minima underneath!
Well that’s all! Hopefully you find it a tad bit easier to read an approach plate!
If you have any questions, feel free to ask!
Have a great one!!!
Also please bear with me, I did this all on my cell…