Since the early days
of flight, angle of attack (AOA) has been a key aeronautical-engineering
parameter and is fundamental to understanding many aspects of airplane
performance, stability, and control. Virtually any book on these
subjects, as well as basic texts and instructional material written
for flight crews, defines AOA and discusses its many attributes.
AOA can be used for many
indications on the flight deck to improve flight crew awareness
of airplane state relative to performance limits. Dedicated AOA
indicators have been used on military aircraft for many years, but
this form of display has not been used often on commercial airplanes.
On Boeing models currently in production, AOA is used to drive stall
warning (stick shaker), stall margin information on airspeed indicators,
and the pitch limit indicator (PLI) on the primary attitude displays.
AOA information is combined with other data and displayed as an
integral part of flight deck displays.
Recent accidents and
incidents have resulted in new flight crew training programs for
upset recovery and terrain avoidance, and these in turn have heightened
industry interest in AOA as a useful flight parameter for commercial
The U.S. National Transportation
Safety Board (NTSB) has recommended visual indication of AOA in
commercial airplanes. This indication may take the form of a dedicated
AOA indicator or other implementation, such as the PLI.
A dedicated AOA indicator
shown on the primary flight display (PFD) recently has been developed
in cooperation with airline customers. The new indicator is offered
as an option on the 737-600/-700/-800/-900, 767-400, and 777 at
During the development
of the new indicator, discussions with airlines, the NTSB, and U.S.
Federal Aviation Administration (FAA) pilots and engineers provided
a unique opportunity to examine potential uses of AOA and the many
existing uses that have evolved in recent decades along with advances
in display and indication technology.
This article discusses
principles of AOA.
performance and AOA.
indications and flight crew procedures in current Boeing production
and uses of a separate AOA indicator.