Technology: Smart rudder boost

Fired up and warmed up, with the clearance copied and loaded, the hardest part of the flight is over and all that remains is a two-hour flight to the lake where the weather is beautiful. The gear comes up, the propellers come back, and the clouds swallow the airplane into a sea of gray.

A smile grows on your face, because hand-flying a Baron is a joy. Your shoulders have just relaxed when it happens: a loud bang, the airplane yaws, and the airspeed starts to decay.

The lives of your family depend on what happens next. Thankfully this story is rare, but too often it has a sad ending.

Higher-performance airplanes have engine-out events that are more dynamic than those of lighter airplanes. Turboprops and jets often have rudder boost to aid the pilot in this critical situation. Light twins have always relied solely on a well-trained pilot to deal with an engine failure in flight.

GFC 600

The Garmin GFC 600 autopilot sets a new standard for autopilots in light aircraft. Its bundle of features called Autonomí includes Garmin Electronic Stability and Protection (ESP), a single-button return to level function, flight director, emergency descent mode, and a new feature announced in December 2020—Smart Rudder Bias for light multiengine airplanes. Recently I was invited to fly Garmin’s BE-58 Baron with the Smart Rudder Bias system installed at the company’s flight test facility in Olathe, Kansas.

Quick action and proper identification of the failed-engine propeller is essential in a light twin. This is best done from memory and known by many as the “The Drill,” and one of the key steps in that process is accurately identifying and verifying the failed engine. Pushing on the rudder to bring the ball back toward center and retarding the throttle on the suspected engine confirm which engine has failed. This is not as easy as it sounds and many a multiengine checkride has resulted in a pink slip for misidentification of the failed engine. Finding the correct amount of rudder “bias” to improve the engine-out flying characteristics of the airplane without masking the failed engine in the “identify” step is a delicate balance.

Garmin believed aircraft with the GFC 600 autopilot, yaw damper, and G500 TXi or G600 TXi electronic flight instrument system with engine information system included all the hardware needed to make dealing with an engine failure easier and safer. All with little more than a software upgrade to the properly equipped Beechcraft BE-58, -58A, and most of the Piper Navajo PA–31-300 through -325CR. More models are coming.

The rudder bias and electronic stability systems work in concert. Stability protection is armed all the time and when the aircraft exceeds bank or airspeed limits the system nudges the airplane back into a less aggressive attitude. It can be easily overpowered manually. Rudder bias is armed when the airplane exceeds its published VMC and engaged when the EIS senses a specified difference in engine power and yaw in the same direction. Engagement of the rudder bias system changes the engagement parameters of the stability protection, which will nudge the airplane back toward wings level at a much lower angle of bank (7 degrees) into the failed engine. If the pilot gets slow stability protection will nudge the nose down to maintain 90 KIAS.

Lowering the nose to protect airspeed decay is critical. Pilots today are learning their multiengine skills in airplanes like the Piper Seminole and the Beechcraft Duchess. These airplanes have benign engine-out handling and large-chord vertical stabilizers which reduce the yaw dynamics when an engine fails. As a result, the critical nature of the VMC event has been downplayed in recent years. Higher performance airplanes with short-chord vertical stabilizers can exhibit very violent VMC characteristics, up to and including a snap roll.

Let’s fly it

The G500 TXi with EIS in the demo BE-58 is a clean installation. Adding Smart Rudder Bias requires no additional preflight actions, and adds no cost to a panel upgrade. The winds were gusting in the high 30s and the ride was rough, but the GFC 600 took it all in stride until the turbulence subsided above 4,000 feet.

Disconnecting the autopilot, I rolled briskly toward 60 degrees of bank. The stability protection started pushing back at 45 degrees of bank. While easily overcome, it encourages reducing bank angle back to 30 degrees. Resisting the stability protection for 50 percent of the preceding 20 seconds, 10 seconds continuously, caused the autopilot to engage. Then the forces became much heavier and the airplane returned to a level attitude. Pressing the A/P disconnect button returned aircraft control to the pilot, and a 5-second press on the red button disabled stability protection completely. Pushing the red button at any time ensures the pilot is flying the airplane.

Simulated engine failures were next. With rudder bias disabled, even with the reduced power available at 4,500 feet, closing the throttle on the left Continental IO-550 produces a significant yaw. At lower altitudes, the power is higher and the yaw dynamics would be more pronounced.

With rudder bias enabled, retarding the throttle on the left engine caused an engine failure annunciation on the pilot’s primary flight display and yaw as expected, but considerably less. Setting zero thrust, the airplane stabilized in yaw at about the one-half ball out of center, which is desired to offset the sideslip caused by an engine-out. While rudder bias is engaged, banking the airplane over 7 degrees into the dead engine activates stability protection, and the airplane is nudged back toward a wings-level attitude. Immediately following an engine failure there can be some chaos and the system will reduce the dynamics in that phase.

In an actual engine failure, the next step is to execute “The Drill” from memory, followed by the engine failure checklist, which confirms the memory items were completed along with the secondary items as needed. The flight manual limitations for the GFC 600 require the rudder bias system to be disabled after the engine is secured. This is unfortunate as the system will fly the airplane in the correct zero-sideslip configuration at, or slightly above VYSE with the pilot’s feet on the floor.

The stability protection nudged the nose down when slowing the Baron below 90 KIAS to maintain that speed. This is a huge feature because many engine failure accidents occur because the pilot fails to maintain adequate airspeed. Whether the pilot is distracted or trying to stretch the glide, getting slow with a failed engine is always a bad idea.

The system is good, but it is not perfect. The power differential is determined by an algorithm of manifold pressure, fuel flow, rpm, and outside air temperature. This is a compromise defined by the sensors installed in the system. In turboprop aircraft, rudder boost is activated by a loss in engine torque, which is a definitive indicator. Should both magnetos fail simultaneously, the system would not be able to detect an engine failure. One could imagine several sensor failures that could preclude detecting an engine failure or annunciate a failure on an engine that might be operating normally. Only time will tell if these issues are a concern. The other concern is whether the system will make it harder to identify the failed engine in a cruise configuration where control forces required to deal with an engine-out are much lower. This could result in misidentification of the failed engine. The EIS system should help, but careful identification and verification of the failed engine in “The Drill” phase is still critical.

It’s all about training

I have experienced engine failures in nearly every phase of flight and watched numerous students do the same in training. The flight dynamics of the engine-out contribute to the chaos that ensues after an engine failure, and calming that is a good thing. But even in turbine-powered aircraft with rudder boost, auto-feather, and lots of excess power, pilots still manage to screw up. Training is the essential element that determines the outcome.

Training is important and the ever-increasing capability and complexity of the aftermarket avionics packages available create an opportunity for improvement in our industry. Pilots routinely drop off a mid-1970s Baron with steam gauges and a Century III autopilot and 30 days later pick up the same airplane with all the capability of the most modern bizjet. A quick flight around with one approach in visual conditions with the avionics tech is not adequate training.

Perfect is the enemy of good, and this is a good system. With almost no additional hardware (an additional switch), Garmin makes the moderately challenging engine-out scenario of a Baron comparable to the benign engine-out handling of a Piper Seneca. That is a big statement, but it is well deserved. Some will be drawn to this system because they see it as a way to buy experience and install it in the instrument panel. It is not that. How the Baron trip described in the opening ends on the fateful day depends on pilot proficiency, not hardware. That comes from good initial, and regular recurrent, training.

Doug Rozendaal is an experienced warbird pilot, aerobatic pilot, and designated pilot examiner.