There has been much discussion about how an aircraft with Tamarack Winglets behaves when a failure occurs. This page is intended to dispel misconceptions and rumors and to bring context to the public. As you can imagine, an aircraft must be demonstrated to be “safe” during failures and that is what certification is all about; Safety. There are very specific FAA regulations that define “safe” in the case of failure modes flight testing.
Certification flight testing included tests of failure conditions, such as single asymmetric deployments and dual (adverse) asymmetric TACS deployments. These failure conditions were shown to be controllable. We have uploaded a video of a TACS runaway or hardover where the TACS is forced into position and held in place at the maximum deflection throughout the event until recovery. Although not a likely scenario, certification requires all types of failures to be flown, at all airspeeds and flight regimes including a fuel imbalance, single engine, crosswinds, etc. For any failure condition, the aircraft must be easily recovered and continued safe flight to landing must be shown. Safe flight is defined as normal pilot skills, normal pilot forces and positive structural margins on the airframe.
In the video below, the aircraft is in level flight at 270 KIAS at 17,000ft with the autopilot engaged. The flight test engineer is in the cabin with the proprietary ATLAS manual control module, preparing to surprise the pilot with a TACS hardover to the extreme position, trailing edge up (worst case) on one side of the aircraft. The pilot is expecting it but doesn’t know when. The pilot needs to recognize the event happened and then respond accordingly. In this video, the pilot is acting very conservatively and does not even touch the controls until the autopilot disengages itself at 30 deg bank. The pilot then initiates a recovery per the AFMS guidance: Throttle at Idle, Speed Brakes Extended, Roll Airplane Level.
In the video, the airplane rolls to a maximum of 30 degrees in about 5 seconds and is recovered in about 4 seconds. Then the airplane is trimmed out, and normal flight is resumed at 160 KIAS. No special skills were needed and you can see it is not a very remarkable experience. It looks like a normal rolling maneuver. Once the airplane is trimmed out, the plane flies normally and it is hard to tell there is a TACS at full deployment - even during takeoffs and landings.
If the pilot were to grab the yoke at the moment the event is recognized, or quickly after that, the maximum bank angle is very small, as you can infer from the video. The benign nature of this improbable failure mode is the reason EASA and FAA, during the initial certification, determined that no special training was needed for our system, and that was verified with the latest review during this AD. They initially determined that it was sufficient to provide a statement in the Flight Manual Supplement we provide to all customers that effectively reads… the aircraft may roll if a failure occurs, here is how to recover. That also has not changed in the latest review during this AD, so effectively the original certification has been verified and validated again.