FAA To Amend Airworthiness Standards to Transport Airplanes

By Mike Mitchell

September 14, 2009, The Federal Aviation Administration proposes to amend the airworthiness standards applicable to transport category airplanes to clarify that flying at or below the design maneuvering speed does not allow a pilot to make multiple large control inputs in one airplane axis or single full control inputs in more than one airplane axis at a time without endangering the airplane’s structure.  

This proposed regulation is the result of an accident investigation and responds to a National Transportation Safety Board recommendation. The results of the accident investigation indicate that many pilots might have a general misunderstanding of what the design maneuvering speed (VA) is and the extent of structural protection that exists when an airplane is operated at speeds below its VA. This action is being taken to prevent this misunderstanding from causing or contributing to a future accident. 

The design standards also consider an abrupt return of the rudder control to the neutral position. The standards do not address full control inputs in more than one axis at the same time or multiple inputs in the same axis. Therefore, the structural design requirements do not ensure the airplane structure can withstand multiple control inputs in one axis or control inputs in more than one axis at a time at any speed, even below VA. 

The NTSB investigation identified what appears to be a widespread misunderstanding among pilots about the degree of structural protection that exists when full or abrupt flight control inputs are made at airspeeds below an airplane's VA. As a result, the NTSB recommended that the FAA amend all relevant regulatory and advisory materials to clarify that operating at or below maneuvering speed does not provide structural protection against multiple full control inputs in one axis or full control inputs in more than one axis at the same time.  

14 CFR 25.1583(a)(3) currently requires applicants to provide the VA, along with the following statement, in the Airplane Flight Manual (AFM): ``Full application of rudder and aileron controls, as well as maneuvers that involve angles of attack near the stall, should be confined to speeds below this value.'' Although the required AFM statement warns pilots against making full rudder or aileron control inputs at speeds above VA, it is silent on what control inputs can safely be made below VA. Pilots may misinterpret the AFM statement to imply that any control input can safely be made below VA. 

At the FAA's request, manufacturers of transport category airplanes voluntarily revised the AFMs for all major transport category airplane types currently in service to include a statement similar to the following: Avoid rapid and large alternating control inputs, especially in combination with large changes in pitch, roll, or yaw (e.g., large sideslip angles) as they may result in structural failures at any speed, including below VA.