How does obstacle clearance change during an approach?

Posted by ShadowSinger2121@reddit | flying | View on Reddit | 4 comments

I heard somewhere that the guaranteed clearance changes depending on which leg of the approach you're on. Something like, 1000' on feeders, 500' after you pass an IAF, and 250' after the FAF. Is that correct?

Reply to Post

4 Comments

[-]

noahhl@reddit

Yes, it changes depending on the segment, location, type of approach, and other factors, but it's not so simple as 1000/500/250 in every case. [FAA Order 8260.3](https://www.faa.gov/documentLibrary/media/Order/Order_8260.3D_vs3.pdf) is 500 pages of detailed rules that procedure designers use. It's not worth reading every page unless you want to become a TERPS elf, but it is worth reading a few sections to get an idea of how procedures are constructed. If you have questions about a procedure you fly frequently, I also encourage checking the [Instrument Flight Procedures Gateway](https://www.faa.gov/air_traffic/flight_info/aeronav/procedures/). You'll often find the exact criteria that were used to design that procedure, including why minima might have changed a few feet in a revision.

[-]

ManNotHamburger@reddit

I thought TERPS elves were summoned in some kind of dark ritual not trained

[-]

Josephyr@reddit

Yes, that's correct. Here's a full breakdown from FAA Order 8260.3D (United States Standard for Terminal Instrument Procedures - TERPS) and ICAO PANS-OPS criteria **Feeder Routes** * Provide at least **1,000 feet** of obstacle clearance. **Initial Approach Segment** * Provides at least **1,000 feet** of obstacle clearance in non-mountainous areas. **Intermediate Approach Segment** * Provides at least **500 feet** of obstacle clearance. **Final Approach Segment** * Provides at least **250 feet** of obstacle clearance in non-precision approaches (i.e., approaches without vertical guidance like an ILS glideslope). * For precision approaches (e.g., ILS), the obstacle clearance is based on the obstacle evaluation area, which includes the **Obstruction Clearance Surface (OCS)** and the required TERPS slope criteria.

[-]

rFlyingTower@reddit

This is a copy of the original post body for posterity: --- I heard somewhere that the guaranteed clearance changes depending on which leg of the approach you're on. Something like, 1000' on feeders, 500' after you pass an IAF, and 250' after the FAF. Is that correct? --- Please downvote this comment until it collapses. --- I am a bot, and this action was performed automatically. If you have any questions, please [contact the mods of this subreddit](https://www.reddit.com/message/compose?to=/r/flying).