Skip to page content

USA Banner

Official US Government Icon

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure Site Icon

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

United States Department of Transportation United States Department of Transportation

AC 120-91A - Airport Obstacle Analysis

Document Information

Airport Obstacle Analysis
Date issued
Office of Primary Responsibility

This AC describes acceptable methods and guidelines for developing takeoff and initial climbout airport obstacle analyses andin-flight procedures to comply with the intent of the regulatory requirements of Title 14 of the Code of Federal Regulations (14 CFR) part 121, §§ 121.177 and 121.189; part 135, §§ 135.367, 135.379, and 135.398; and other associated one-engine-inoperative (OEI) requirements relatingto turbine-engine-powered airplanes operated under parts 121 and 135. The methods and guidelines presented in this AC are neither mandatory nor the only acceptable methods for ensuring compliance with the regulatory sections. Operators may use other methods if those methods are shown to provide the necessary level of safety and are acceptable to the FederalAviation Administration (FAA). This AC need not serve as the sole basis for determiningwhether an obstacle analysis program meets the intent of the regulations. However, the methods and guidelines described in this AC have been derived from extensive FAA and industry experience and are considered acceptable to the FAA when appropriately used. Mandatory wordssuch as “shall” or “must” apply only to those who seek to demonstrate compliance to a specificrule by use of a method set out in this AC without deviation. The contents of this document do not have the force and effect of law and are not meant to bind the public in any way. This document is intended only to provide clarity to the public regarding existing requirements under the law or agency policies.