SAIB aims at better V-speed understanding

January 20, 2011

Think you know your V-speeds? The FAA has released a special airworthiness information bulletin (SAIB) providing information to pilots after determining from a crash investigation “that many pilots have a misunderstanding of what the design maneuvering velocity (speed), V A, represents.”

The investigation followed the Nov. 12, 2001, crash of American Airlines Flight 587, which killed all 260 people on board and five people on the ground. The NTSB determined that the vertical stabilizer separated in flight “as a result of the loads beyond ultimate design loads that were created by the first officer’s unnecessary and excessive rudder pedal inputs.”

“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,” the FAA said in the SAIB. “This is not true.

“The design maneuvering speed ( V A) 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.”

The SAIB states that even though the accident aircraft was operated under Part 25, the concept of maneuvering speed is relevant to all types of airplanes. It explains that the regulations governing airplane structure design strength require adequate strength for full control deflection below V A—but that manufacturers are not required to make airplanes strong enough to withstand full control input in one direction followed by full input in the opposite direction, or for more than one full control input.

This type of education—bridging the gap between what manufacturers test and what pilots think they test—was among the recommendations provided by an industry study of the certification process for Part 23 aircraft. AOPA chaired the study’s pilot interface working group that discussed flight testing, operation, and pilot training, and found a disconnect between aircraft certification and operation. In 2009, the group suggested more emphasis on pilot understanding of V speeds and the protection actually given at those speeds, among other recommendations.

The SAIB also explains that the V A number published in an airplane flight manual or pilot’s operating handbook is valid for operation at a specific gross weight, typically max gross weight. V A decreases as the airplane’s weight decreases. It recommends pilots reduce V A when operating below gross weight according to the following formula: V A-NEW = V A √(W NEW­/W MAX-GROSS).