What is ONSPEED?
Optimum Approach, Landing and Maneuvering Angle of Attack
The ONSPEED Concept
ONSPEED is an angle of attack that is used for approach, landing and maneuvering flight. ONSPEED AOA is always the same. It's not affected by bank angle (G load), gross weight or density altitude. ONSPEED AOA is a function of L/Dmax AOA, which is a fundamental AOA that is designed into the airplane. ONSPEED AOA is not an airspeed. It is optimum AOA for approach and landing. It helps turning base to final and achieving stable parameters prior to the flare. It's a "just right, not too fast and not too slow" energy condition for landing. The tone allows the pilot to hear ONSPEED and provides easy to interpret cues to make pitch corrections. When the airplane banks, the tone automatically compensates--all the pilot has to do is adjust pitch based on tone cues to maintain a safe, optimum AOA for maneuvering, approach and landing. If the pilot maintains ONSPEED, the airplane cannot stall.
Why a Tone Instead of a Visual Display?
Hearing is an under-utilized cockpit resource. The aural AOA logic is a sonic image--literally an intuitive mental picture of ONSPEED or "fast" or "slow" relative to ONSPEED. There is no requirement to look inside the cockpit. The tone tells you how hard to pull or relax pressure on the stick or yoke to maintain ONSPEED angle of attack. It also tells you when you are at L/Dmax and provides progressive stall warning. These are the three key aerodynamic performance parameters when operating on the "backside" of the power-required curve. The airplane cannot stall when ONSPEED, and the aural logic assists with maintain positive aircraft control during maneuvering.
The fighter community in the US military was an early adaptor of angle of attack instrumentation and developed energy management tools for pilots. This small group of highly trained aviators has extensive
experience flying with AOA references and aircraft handling techniques designed to maximize aircraft performance (with a respectful nod to glider pilots and the soaring community!). The ONSPEED concept was developed by the military beginning in the late 1950's and first applied to approach and landing operations. The ONSPEED aural AOA logic was originally fielded in the McDonnell F-4 Phantom in an effort to reduce loss-of-control mishaps during maximum performance maneuvering as well as assisting during pattern operations--It proved to be highly effective. All US fighters use angle of attack as the primary reference for approach and landing, including landing aboard ship.