The FAA issued a Special Airworthiness Information Bulletin (SAIB) Jan. 18 in the wake of a crash investigation that revealed “many pilots have a misunderstanding of what the design maneuvering velocity (speed), VA, represents.”
While the informational bulletin stems from an airliner accident, the information applies to pilots of all certificated planes, as well as special light-sport category airplanes (S-LSA), experimental light-sport airplanes (E-LSA), and experimental amateur-built airplanes, according to FAA officials.
On Nov. 12, 2001, American Airlines Flight 587 crashed shortly after takeoff from New York’s John F. Kennedy International Airport, killing all 260 people aboard and five people on the ground. The National Transportation Safety Board (NTSB) determined “the probable cause of this accident was the in-flight separation of the vertical stabilizer as a result of the loads beyond ultimate design loads that were created by the first officer’s unnecessary and excessive rudder pedal inputs.”
In the SAIB, FAA officials note that “many pilots believe that as long as the airplane is at or below this maneuvering speed, they can make any control inputs they desire without any risk of harm to the airplane. This is not true. The design maneuvering speed (VA) is the speed below which you can move a single flight control, one time, to its full deflection, for one axis of airplane rotation only (pitch, roll or yaw), in smooth air, without risk of damage to the airplane.”
“Even though experimental airplanes may not have a published VA, they will still have some maximum maneuvering speed associated with the maximum structural design loads,” the SAIB continues. “Therefore, the pilot should be aware of what speed this is.”
Regulations governing the design strength requirements for airplanes require adequate strength for full control deflection (below VA). However, they do not require the manufacturer to make the airplane strong enough to withstand full control input followed by a full control input in the opposite direction, even below VA. Neither do they require the manufacturer to design the airplane for more than one simultaneous full control input, such as full ailerons with full elevator and/or rudder, according to the SAIB.
VA, as published in the airplane flight manual or pilot’s operating handbook, is valid for operation at the gross weight stated, which is typically at max gross weight.
“It is especially important to note that VA decreases as the airplane weight decreases,” the SAIB said. “At first, this may seem counter intuitive. All pilots understand that when the airplane is subjected to an external force, such as the aerodynamic force from a control surface, the airplane responds by accelerating (rotational acceleration) about one of the airplane’s axes.”
This higher acceleration gives rise to higher loads on the airplane structure. Therefore, as the airplane weight decreases, the allowable maneuvering speed must also decrease, to ensure that the airframe is not damaged.
Recommendations in the SAIB include:
- Do not apply a full deflection of a control, followed immediately by a full deflection in the opposite direction.
- Do not apply full multiple control inputs simultaneously; i.e., pitch, roll and yaw simultaneously, or in any combination thereof, even if you are below VA.
- Reduce VA when operating below gross weight.
For more information: FAA.gov