TERPS 101

Since we trust our lives to procedures designed to TERPS standards whenever were in the soup, lets pull back the curtain just a little bit to see whats going on behind the scenes of our approach charts. Note that collectively the TERPS standards easily run over 1000 pages and often involve quite a bit of math, so this is intended to be an overview and is by no means exhaustive. We will be looking at basic concepts and how they apply to approach procedures in this article; in a future article well discuss standards for other phases of flight.

IFR Staff

Monday, October 28, 2019 at 12:00 AM ET

Verified

Key Takeaways:

TERPS (U.S. Standard for Terminal Instrument Procedures) is the fundamental set of standards defining acceptable criteria for ensuring flight safety on Instrument Flight Rules (IFR) procedures, primarily focused on obstacle and ground clearance.
Its core concepts, such as Required Obstacle Clearance (ROC), Obstacle Evaluation Areas (OEA), and Obstacle Clearance Surfaces (OCS), define obstacle-free airspace under various flight segments.
TERPS comprehensively addresses uncertainties by accounting for navigation errors, potential inaccuracies in obstacle location data, and assuming unknown obstacles (Adverse Assumption Obstacles) where data is lacking.
These rigorous standards directly determine instrument procedure minimums (e.g., Decision Altitude/Height, Minimum Descent Altitude, visibility) and are legally binding, forming the basis for all published approach charts.

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Successfully flying instruments requires several ingredients. There are the skills, knowledge, and reflexes developed during training. Varying amounts of technology must be in working order. However, the most fundamental requirement for the existence of IFR flying is literally blind trust. We trust (and hopefully verify whenever possible) ATC to keep us clear of traffic, and we trust our instrument procedures to keep us safe while navigating (it’s a bit harder to verify that one).

Putting this trust into human controllers and procedure designers who are just as fallible as anyone else is no small task, but it is mitigated by the existence of required standardized operating procedures. This doesn’t mean they are always done perfectly, but they statistically provide an acceptable level of safety.