We pilots routinely kill ourselves. Not only is this a bummer for the people intimately involved in the wreck, its also bad for business. Cirrus Aircraft defined itself as a trend-setter in combatting this with certified aircraft when the first SR20s rolled off the line with whole-airframe parachutes in 1999. Better than just surviving a catastrophe at the expense of the airplane, however, would be recovering back to controlled flight. Cirrus again led the charge in light GA with “LVL” button as part of the Garmin Perspective avionics suite (a modified G1000) in 2008. More sophisticated than a simple rip-cord solution, the LVL (blue) button leverages the tumble-proof digital “gyros” to pitch and/or roll the aircraft back to level flight without overstressing anything. Avidyne came up with a similar feature called “Straight and Level” in its DFC 90/100 autopilots. This makes the feature retrofitable to aircraft formerly equipped with the STEC 55X. Both Garmin and Avidyne have protection against going too fast or too slow-in some cases even when the autopilot is technically turned off. This is taking us into uncharted territory: these autopilot systems can actually disobey the pilot for that pilots own good. All Airbus and “Im sorry, Dave. Im afraid I cant do that” pot shots aside, this begs the questions of whether these systems really work, whether they are worth the expenses, and, more philosophically, is this a direction we want to go? Right now the only contenders in small, certified aircraft is the Cirrus Perspective system and the Avidyne DFC-series, so we’ll focus on those.
Smart autopilot Tricks
Step one is clarifying what the systems do and don’t do. Weve tried both the Perspective and the DFCs one-button recovery to level flight. They work as advertised. The systems are even smart enough to unload the wings before attempting to roll level and pull up. Unofficial (but we’ll say reliable) sources have told us the DFC has even demonstrated recoveries from inverted dives. We expect the Perspective would do the same.
Both systems also have under- and overspeed protection when the autopilot is engaged. If the pilot commands a climb without adding sufficient power, such as during a botched missed approach, and the aircraft will slow to a specific speed and then pitch down just enough to hold that speed. Meanwhile, beeps, flashing text, and audible callouts will warn “Underspeed Protection Active.” Restoring power will restore the climb and disable the mode. Again, we tried it and it works.
The Avidyne system uses a similar tactic of the pilot commands a descent that crosses Vne: It pitches up. The Perspective system is different. It only offers overspeed protection with the Electronic Stability and Protection (ESP) thats part of the $39,900 Perspective 700 Select package. ESP was also retrofit on many Perspective SR22s sold before the function was offered.
ESP runs full-time, even with the autopilot off. If you overspeed the airplane, either by commanding too much descent on autopilot or by manually pitching down, the autopilot servos push back on the stick to slow the plane from 200 knots to 190 knots. Yes, the autopilot could be pitching down because you told it to descend, and then pitching back up not to overspeed-in an endless loop until the pilot fixes the problem. Good thing it isn’t smart enough to need psychotherapy.
Its only 10 pounds of force, so you could easily override it. In fact, when we tried a manual dive in an ESP Cirrus, we found the push subtle given the higher stick forces at 200 knots. The combination of the push and the visual and auditory warnings should get a pilots attention, however.
ESP also limits pitch and roll. Pitching to 17.7 degrees nose up or 16 degrees nose down will earn you that same 10-pound pushback toward level flight. Rolling past 45 degrees of bank will generate a five- to seven-pound push on the stick back toward about 30 degrees of bank along with only a subtle visual cue (see sidebar, page 9). An ESP aircraft (Garmin has the system running on some other G1000-equipped aircraft) cant get into a steep spiral. It may spiral and descend, but the bank will keep oscillating between 45 and 30 degrees. ESP can be temporarily disabled at any time if the pilot chooses.