Definition
An FAA Advisory Circular that provides guidance for pilots of large aircraft on ground deicing and anti-icing procedures, including pre-takeoff contamination checks, holdover times, and the use of deicing/anti-icing fluids. It is referenced in icing-related training material as a primary source of recommended practice for operating in winter conditions.
Plain English
An FAA guidance document that tells pilots how to handle ice, snow, and frost on a large aircraft before takeoff — what to spray on, how long it lasts, and how to check the airplane is clean enough to fly.
Context Anchor
Seen in FAA handbook references when a topic points pilots to more detailed information about aircraft icing and ground deicing.
Derivation
An Advisory Circular (AC) is the FAA's standard format for non-regulatory guidance. The number 120-58 places it in the 120 series, which covers air carrier and commercial operations.
Why Pilots Care
Ensures pilots stay within legal duty limits to maintain safety and avoid violations.
Intuition Check
Do not read “Advisory” as “optional and safe to ignore.” In FAA use, an Advisory Circular is official guidance, even when it is not a regulation by itself.
Example Sentence 1
Before departing on a snowy morning, the captain referenced AC 120-58 to confirm the holdover time for the Type IV fluid being applied.
Example Sentence 2
Chapter 4 summary referenced AC 120-58 for details on rest requirements during instrument training.