I was trying to get a list of all ILS approaches in the US, which brought me to the FAA Aeronautical Product Release API to retrieve all the DTPP (Digital-Terminal Procedures Publication) as five zip files.

I noticed the naming conventions of the files began with a five digit number (left padded with zeros). For instance, SEA ILS RW 16C (CAT II & III) had the name: 00582I16CC2_3.PDF

Although it is easy enough to parse out the remainder of the name (I for ILS, 16 is the RWY, ...), it was this five digit number I was most interested in.

Previously, I happened to noticed that all approaches at a single airport had the same AL number at the top of the approach (at the time, I didn't even know what AL stood for). See the top margin: enter image description here

Aeronautical Chart Users' Guide

I went to the Aeronautical Chart Users' Guide and found in the Section Instrument Approach Procedure Chart under U.S. Terminal Procedures Publication (p.98 on 2/23/24) some information:

At the center of the top margin is the FAA numbering system. This Approach and Landing (AL) number is followed by the organization responsible for the procedure in parentheses, e.g., AL-18 (FAA). Military procedures do no show an AL number, but do show the appropriate authority for the procedure, e.g., (USAF).

My questions:

  1. Where can I find the mapping of Approach and Landing numbers to "organization responsible for the procedure in parentheses"?

  2. Are these "organization's" just airports? Or might it include something that aggregates multiple airports in disparate locations?

  3. Does anyone know where to find the document that would describe the DTPP naming convention?



2 Answers 2


00582 in 00582I16CC2_3.PDF is the airport code in the metafile for the approach places. On the D-TPP website, you can find an XML file in the 'E' download ZIP file that will map the procedure to the file. These files are used by many companies to provide charts to users. i.e. Foreflight, FltPlan Go, etc.

You can also download the metafile XML file separately from the bottom of this website. https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/dtpp/search/

FAA digitial approach Metafile

In the metafile, you can search for <alnum="582"> and you will find the XML data for Seattle Tacoma Washington Airport KSEA.

<airport_name ID="SEATTLE-TACOMA INTL" military="N" apt_ident="SEA" icao_ident="KSEA" alnum="582">


I assumed the airports database "SITE_NO" is the same as the AL numbering system on the approach plates. The SITE_NO value for KSEA is 26395 and it is not the AL NUM. It is interesting to dig into the data freely given by the FAA though.

If you want to dig into the data a little more, you can download the 28 Day NASR Subscription where you can find the airport table linking the airport name to the primary key found in the procedures name. https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/NASR_Subscription/

  • $\begingroup$ Thank you so much, @wbeard52. I have spent the afternoon digging into these. It is incredible how much data is in here, and getting the 28DaySub*, unzipping and exploring the CSV's was invaluable. However, even after digging through all of this, I still haven't made the connection to that original AL-582. The best connections I found were AP_BASE.csv and APT_BASE.csv, in which the SITE_NO (primary key?) for SEA-TAC is 26395. But no reference to this AL-582, 582, or 00582. A full text search has thousands of hits for 582, as a number, so I could be missing it. Any other thoughts? $\endgroup$ Commented Feb 25 at 1:13
  • $\begingroup$ Brilliant! Thank you for that follow up of the alnum="582". I am curious if there is an effort to aggregate, present, and query this information in a tractable way. Thank you again for your help and explanation! $\endgroup$ Commented Feb 25 at 20:14
  1. AL numbers and the Office of Primary Responsibility (OPR, represented by the letters within parenthesis) are separate items. The AL number refers to the specific airfield. The idea was that if an airfield ever changed its name, identifier, or the name of the closest city, the AL number would remain the same. The first one was and continues to be Abilene Rgnl in TX. The OPR, on the other hand, is the office/agency responsible for that particular procedure. For example, the FAA may be the procedure designer for civil procedures, but the USAF may be the responsible organization for the high altitude procedures at the same airfield.
  2. As indicated in 1, these organizations may be the FAA, an outside agency that develops the procedure that is then certified by the FAA (FAA-O), the US Army, the US Air Force, the US Space Force, or the US Navy. The DoD no longer shows AL numbers on charts, hence the part “Military procedures do not show an AL number, but do show the appropriate authority for the procedure, e.g., (USAF)”
  3. I can’t help you with this one, but the naming convention typically includes the AL number, the approach type, and runway number.

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