Older turboprop twins get a new autopilot option, starting with Twin Commanders
There are thousands of aging twin-engine turboprops, and almost all of them have autopilots from another era. In most cases these older autopilots function well. Older units get their inputs from conventional gyro-stabilized platforms or, in avionics jargon, iron gyros. Their pneumatically or electrically driven rotating components sense roll and pitch, and the analog signals they send to the autopilot are continuous.
But these analog autopilots have been surpassed by the march of technology. Now, digital platforms, autopilots, and flight control systems are the rule, and for good reason. Analog signals can be interrupted or degraded by electromagnetic interference or precipitation static. Today's digital signals — a clean, noiseless stream of 1s and 0s — have the reliability and repeatability (consistent signals) that elude analog-based autopilot inputs. Perhaps more significant is that service and parts for older autopilots are rapidly becoming scarce.
Back in April, Meggitt Avionics/S-Tec certified the MAGIC 2100, the first digital flight control system (DFCS) designed to upgrade older turboprops from analog to digital technology. The Twin Commanders 690A and 690B were the first airplane models to receive supplemental type certificates (STCs) for the MAGIC 2100. Meggitt says it will go for approval in other twin turboprops, in this order: Cessna Conquest II; Beechcraft C90 King Air; the Twin Commander 840/900/980/1000 "Jetprop" series; the Cessna 425; and the Beechcraft Model 200 King Air.
The 2100 has plenty of functionality, intuitive controls, and an easy-to-read liquid-crystal display. At this point, it's certified to work only with Meggitt's MAGIC EFIS (electronic flight information system) — a central STCed feature of the Twin Commander Aircraft Corporation's "Renaissance Commander" upgrade program. This EFIS comprises a four-tube set of flat-panel, active-matrix color liquid-crystal displays — all 4.5 inches high and 5.3 inches wide. There's a primary flight display (PFD) and navigation display (ND) in front of the pilot, and two engine and instrument display system (EIDS) tubes to their right.
The autopilot uses an air data attitude heading reference system (ADAHRS) and associated sensors as its reference platform — in other words, to tell the autopilot the airplane's altitude, airspeed, and attitude (roll, pitch, and yaw). Instead of traditional spinning gyros, the ADAHRS uses vibrating quartz elements oscillating at a precise frequency to sense rate and acceleration. This data is sent on an ARINC 429 digital data bus to both the autopilot and EFIS units. Compared to gyroscopic reference platforms, the ADAHRS offers increased reliability and weight savings.
The 2100's two-line, split-screen display shows the active autopilot modes on the top lines, and the armed modes on the lower lines. An Up/Down push-button switch is used to select or change the airplane's airspeed or vertical speed, and a rotary knob is for selecting target altitudes. A series of push buttons across the bottom of the control panel is used to activate or deactivate the various modes: HDG (heading hold); NAV (en route nav tracking); APR (for VOR, GPS, localizer, and ILS approach procedures); REV (reverse sensing, for back-course approaches or tracking); IAS (airspeed hold); VS (vertical speed); ALT (altitude hold); and MNU (menu, for selecting screen brightness and modifying voice annunciations).
Voice annunciation is provided for several conditions. There's a "trim in motion" call-out whenever the electric pitch trim is operating, and a "check pitch trim" voice pipes up if an out-of-trim condition exists for more than three seconds. Altitude call-outs include those for 1,000 and 200 feet before a selected altitude is reached, plus a "check altitude" annunciation if the airplane deviates from a selected altitude by 200 feet or more. "Autopilot disconnect" is another voice call-out.
A test flight in a MAGIC 2100-equipped "Renaissance" Twin Commander showed off this flight control system's integrated capabilities. Except for takeoffs and landings, I flew the airplane using the whole range of the 2100's functions. Right after liftoff, I engaged the autopilot at 800 feet agl simply by pushing the AP button. This automatically commands the airplane to maintain its current pitch and roll attitudes. Pushing AP also enables the system's flight director and yaw damper. HDG and PITCH appeared in the display windows.
For vectors in the climb, the airplane followed the heading bug on the PFD's compass rose. Then the target altitude of 14,000 feet was dialed into the integrated altitude preselect using the inner and outer knobs of the ALT SEL rotary knob. With the UP button, a climb rate of 2,000 feet was selected. Now the display read VS 2000 on the top line and, on the lower line in smaller numerals, the armed altitude of 14,000 feet.
The voice counted down until the altitude hold captured, and ALT HOLD popped up on the top line, with 14,000 beneath it.
Our en route legs were flown using GPS, and the 2100's top line reminded us by showing NAV in large letters and GPSS (GPS roll steering, another feature) in smaller letters. Now the airplane would automatically fly the legs and make course changes — including any arc-entry procedures for instrument approaches — without the pilot having to touch a thing. For my GPS Runway 35 approach to the Bloomington, Indiana, airport, I pushed the APR button and APR and GPSS were annunciated. The descent was programmed with the VS button, and the descent rate was selected with the DN button. Down we went. From our direction of flight this particular approach uses a T-type entry beginning at the BEWHY initial approach fix. The 2100 hit BEWHY, tracked it for four miles or so, gracefully cut the corner at the final approach fix, intercepted the final approach course, then nailed it all the way down. All I had to do was reduce power, lower the flaps, and extend the landing gear.
VOR and ILS approaches are flown almost the same way; just make sure that your nav source selector is in the NAV or VLOC position. At the missed approach point or decision height, the 2100 can be disconnected using the yoke-mounted disconnect button, by pushing the GA (go-around) button on the yoke, or by pressing the AP button on the autopilot control panel.
For ILS approaches, the missed approach altitude can be set in the altitude preselect once you've captured the final approach altitude and before glideslope capture. If you have to perform a missed approach, hit the go-around button on the control yoke. Press the ALT SEL button once, and the missed approach altitude will appear in the display. Fly the flight director command bars, hit the AP button once you're at a safe altitude, and you're on your way to the missed approach fix.
The 2100 anticipates steep turns very well. At one point in my flight demonstration we deliberately approached a final approach fix at a 120-degree interception angle — something that theoretically would never happen in real IFR flying. Using a 30-degree bank, the autopilot guided the airplane through the turn very smoothly.
The MAGIC 2100 sells for $65,900. This is a complete package that includes the ADAHRS; roll, pitch, yaw, and trim servos; and all the customary switches associated with a high-end autopilot. Installation times have been running approximately 120 hours in the Twin Commander. The Meggitt EFIS system goes for $53,900, and includes its own ADAHRS.
E-mail the author at [email protected].
For more information, contact Meggitt Avionics/S-Tec at 940/325-9406, or visit the Web site ( www.s-tec.com).
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