Avidyne DFC90 Autopilot Review

Avidyne DFC90

Feature Rich Autopilot to Compete with GFC 700

Over the years I have had the pleasure of flying and providing instruction in a number of aircraft.  During that time I have had the opportunity to fly behind many different autopilots.  The list includes Bendix King KAP 140, KFC 150, KFC 200, KFC 225, KFC 250,  STEC 20/30, STEC 60-2, STEC 55X, STEC 550, STEC Magic 1500, STEC 2100, Sperry SPZ 500, Collins 106 and 107, Cessna 400, Cessna 800B IFCS, Cessna 1000 IFCS  and Garmin’s GFC 700.  Over the years as technology has increased greatly, and in the last four or five years at a breakneck speed, the new innovations in avionics have greatly increased safety and when used properly can increase situational awareness.  Of course there is no replacement for that moving map every pilot has between the ears, a pilot’s ability to visualize his position is extremely important to becoming a safe pilot especially when operating in the IFR environment.

KFC 150 faceThe PA46 Malibu started out with the KFC150 autopilot in 1984.  This autopilot stayed with the airframe until the end of 1998 (this included the transition from Malibu to Mirage in 1989). It was a very good autopilot and remains so to today. It is an attitude based autopilot which means that it relies on the attitude indicator output for operation.

 

In 1999 Piper began to install the KFC 225 autopilot.  The KFC 225 autopilot was only offered in 1999 model aKFC 225 Autopilotircraft.  The KFC 225 is a digital autopilot which is attitude based.  The altitude preselect is integral to the KFC 225. The KFC 225 proved to be a capable autopilot.  Many PA46 JetProp owners have chosen the 99 model for conversion to the JetProp since it is only year model which used the KFC 225.

 

In 2000 the Mirage was given the STEC 55 autopilot to replace the KFC225.  This was a departure from the previous attitude based system.  Attitude based system55xautopilot system are generally more responsive than rate based systems.  Does this mean that the STEC 55 could not handle the Mirage, the answer is no but the attitude systems are more responsive and seem less prone to deviations.  The downside to the attitude based systems is that they relied on inputs from a mechanical indicator.  Enter the glass revolution and now more and more aircraft have AHRS (Attitude Heading Reference System) which provide a much more stable attitude reference to the autopilot.

The DFC90 was made available to the PA46-350P Mirage about 10 months ago (Avidyne or Aspen equipped).  It is an attitude based autopilot system which utilized the inputs from the ADAHRS (Air Data and Attitude Heading Reference System).  These AHRS systems are embedded in the Avidyne Entegra or Aspen Pro PFD.  The AHRS system produces an more accurate and stable output than in previous analog attitude systems which relied on output voltage to drive the Flight Director and Auto Pilot.  As a result of these outputs the DFC90 can control the aircraft with accuracy and stability not found before in previous autopilots.  The GFC700 also has this capability, but is not available for retro fit to any aircraft separate from the G1000 system.

The DFC90 offers the functionality formerly only available to autopilots found on turboprops and jets.  The autopilot has four vertical modes (Pitch, IAS, VS, or Altitude Hold).  If the pilot pushes the AP button the autopilot and flight director immediately engage and will hold the aircraft current pitch and bank.  I have found this function to be quite useful in the beginning of the missed approach phase.  To operate IAS mode the pilot simply uses the knob on the AP to input the desired airspeed and the autopilot will vary the pitch to maintain the selected airspeed.  Before takeoff the pilot can set the Flight Director to indicate a pitch to hold an IAS or VS, and also may be set for a HDG, NAV course or GPSS.  One thing to remember when using the IAS mode before takeoff is that if you select any airspeed it will show that you should pitch down.  This is normal because the FD bars are telling you to lower the nose to accelerate to the selected airspeed.  The Vertical Speed mode may be selected by the VS knob on the autopilot or on the PFD.  The altitude hold mode simply maintains a captured altitude, but it does have a feature not normally found in GA autopilots.  If the pilot adjusts the altimeter setting after capturing the altitude the AP will acquire the new altitude once the altimeter has been changed.  One standard operating principle in the DFC 90 is the active and armed modes.  The active mode buttons are in green while the armed modes are in blue.  This is true for both lateral and vertical modes.

The DFC90 has five lateral modes. They are Roll, HDG, NAV, GPSS, and APPR modes.  The roll mode is engaged when the AP is engaged with no other lateral modes selected.  As with Pitch mode it engages at the current roll attitude when the autopilot was engaged.  So if you are in a 10° bank when engaged it will hold that bank angle. The only way to change Pitch/Roll is via the Control Wheel Steering button. Simply hold the CWS button while setting pitch and roll to desired setting when released the autopilot will maintain that pitch and bank. The Pitch/Roll mode is very helpful on a missed approach as the pilot can pitch up and initiate a bank/wings level until the GPS is sequenced to the MA procedure.  HDG mode is standard in that it maintains the HDG much as other AP’s do.

The DFC 90 is very smart when it comes to transitioning from GPSS mode to APPR mode.  One of the shortfalls in the 55X is that when you were flying either a LPV or LNAV+V you need to make sure you were not in GPSS mode or the autopilot would not capture the GP.  The DFC 90 will automatically cycle from GPSS to NAV/APPR mode when the GP comes alive (sometime before the FAF).  When the GPS begins producing the GP the DFC90 automatically switches out of GPSS mode and switches to NAV/APPR mode and arms the GS/GP.

 dfc90apprgsarmed

The DFC90 also has an additional mode not found on any other autopilot.  The Straight and Level button can aid a pilot in recovering from an unusual attitude.  The Straight and Level button does have its limitations though.  The maximum demonstrated limits for engagement of the straight and level mode are 60° bank and 30° bank.  Above this limit the mode MAY work but no guarantees.  While testing this mode I put the aircraft in a 50° bank and 20° pitch up attitudes, the straight and level button returns the airplane crisply to a wings level and 2° pitch up attitude.  It should be noted that in a steep pitch down attitude the autopilot may exceed Vne during the recovery process.

The DFC90 has built in speed based envelope protection.  This protection makes it very unlikely that the pilot could get into an auto pilot induced stall.  The system is designed to keep the airplane at or above 1.2 VS1.  The autopilot will reduce bank and pitch attitude to keep the aircraft within the protected envelope. In addition to low speed protection the autopilot also has the capability to adjust for high airspeed protection. At higher airspeeds near Vne the autopilot will reduce pitch to keep the aircraft near maximum speed. In addition to this protection the autopilot is also able to monitor and alert the pilot with envelope protection even when the autopilot is not engaged.  With the autopilot engaged theoretically the aircraft should not stall, but there are exceptions.  Since the system monitors only airspeed there is a possibility that with ice accumulation the stall speed will increase, and the airplane will stall at a higher airspeed.  All in all the system is a good reminder and should increase safe operation both with the autopilot engaged and not engaged.

Avionics have advanced very quickly, and it seems that the majority of the developments have come in the way of panel mounted GPS, MFD’s, weather detection (XM, Stormscope), and traffic detection (Skywatch, TAS610, etc) systems.  Autopilots have lagged somewhat behind in new developments (don’t believe me look at the majority of twin Cessna fleet still flying with original autopilots).  Avidyne has developed a relatively low cost feature rich autopilot which could end up with multiple applications.  Currently the autopilot is available or in process of approval  for Cirrus, Piper Malibu Mirage, Piper Matrix, Cessna 182, Beechcraft Bonanza, and Beechcraft Baron.   In the foreseeable future I would not surprised to see this working its way into such aircraft as the Cessna 340, Cessna 414, Cessna 421, Cessna 210 (T210&P210), and then possibly into the light turbine market (King Air, Cheyenne, Conquest).

Here is a top ten list of my favorite GFC 90 features.

  1. IAS hold mode is an excellent way to manage climbs.
  2. GPSS to APPR automatic switching.  Works very well.
  3. AHRS compatibility.  The digital AHRS signal helps the autopilot be smooth and accurate.
  4. Rock solid performance.  Hold courses, headings, and altitudes perfectly.
  5. Attitude based autopilot.  This allows it to be used in a wide range of aircraft from fast to slow.
  6. FD/AP annunciation.  When FD only is on the V-Bars are green engage the AP they turn magenta.
  7. When the altimeter is reset the autopilot will automatically recapture the altitude preset.
  8. The autopilot is integrated with altitude preselect and vertical speed on both the Avidyne Entegra and Aspen systems.
  9. Envelope protection is a nice safety feature.
  10. In a pinch the straight and level button may come in handy.

 

The author Daniel Moore provides insurance approved initial and recurrent training in PA46 Malibu, Mirage, Matrix, Meridian, JetProp.  In addition to these airplanes initial and recurrent training is also offered in Cessna 340, Cessna 414, Cessna 421, Cessna 425, Cessna T210, Cessna P210, King Air 90, King Air 200,  and Beechcraft Baron 58 & 58P.

 

 

 

 

Systems Knowledge is VIP

Why You Need to Know Your Aircraft Systems.

Providing initial and recurrent training (or any transition training) requires the instructor to decide what items to emphasize. Because time is always limited an instructor cannot always cover every system in detail down to every screw, wire, resistor, solenoid, etc.  Not to mention the fact that going too far into detail and the student will get the glazed over look and be off in their daydreams cruising along in their new airplane.   As an instructor the decision has to be made as to what items to cover in more depth.  This is where the experience of the instructor can really aid the learner in knowing what systems are more troublesome for a particular airframe As an instructor I have been on both sides of the training table. (In addition to being an ATP/CFII I am also an A&P Mechanic).

Occasionally when instructing I am asked the question, “If there is nothing I can do about this system why do I need to know about it?”  While that is a perfectly valid question the truth of the matter is that you never know when systems knowledge will benefit a pilot.  The benefit of knowing a system will expose itself when dealing with either an in flight problem or when assisting a mechanic in dealing with maintenance problem.  Being able to accurately describe a problem and lead the mechanic in the right direction can reduce downtime and costs.  The problem is that you need to be able to speak the language.  Clients have told me, “I just tell the mechanic that it is broke.”  While that might seem an acceptable answer, you can save yourself aircraft downtime and money by accurately describing how the system is not functioning properly or perhaps you can streamline the troubleshooting process.

Let me give you an example from my own experience. I had flown to an area that had received about 4-5 inches of snow.  The airport was in the Southeastern U.S.  and not accustomed to getting snow in the winter and therefore did not have snow removal equipment.  The snow was melting quickly and the runway was 90% clear except for some patches of slush on the runway.  We elected to depart and had fairly normal take off except that we ran through some of those patches of slush.  I believe that slush was thrown up into the nose gear well by the nose wheel.  After retracting the gear we began our climb up t0 10,000 ft our initial assigned altitude.  I began working through the climb checklist stored in the Garmin 430.  When I reached the pressurization check item I noticed that the cabin was climbing at 1,000 fpm, and that I still had no pressure differential reading on the gauge.  At this point I began normal checks to make sure that controls were in the correct position for the aircraft to pressurize.  I checked the Cabin Pressurization Knob, Cabin Dump Valve Switch, Pressurization Controller Setting, and the Cabin Rate Knob on the controller.  All of these controls were positioned in the proper position.  The Cabin Press Knob was all the way in, Dump Switch was in the normal position, and the controller was set for a cruise altitude of FL190.  This is where I began to process my systems knowledge to think of why the aircraft would not pressurize.  This is when the proverbial light bulb went on.  I started thinking about taking off and going through the slush.  It was possible that the squat switch had frozen in position due to some slush getting onto it and since the temps was hovering right a freezing a little cold air mixing with slush/water and the switch could be frozen in place.

The squat switch for the PA46 Malibu is located on the left main gear.   The reason that the squat switch is tied to the pressurization system is to prevent the aircraft from landing pressurized.  In the event that the pilot has improperly set the pressurization controls (another article for a later date) the squat switch will be activated  upon landing which will power to the dump solenoid.  When the dump solenoid is activated aircraft system vacuum will open the safety valve which will immediately dump the cabin pressure.  This is basically the same procedure that happens when the cabin dump valve switch is activated, except the ground for the system comes through the dump switch rather than the squat switch.

In my case since the squat switch was frozen closed the safety valve was still wide open, and therefore I could not pressurize.  Not being able to pressurize on this flight was a problem, as I needed to climb about 15,000 ft. to be able to get above the icing conditions, not to mention at FL190 I have a generous tailwind which factored into my fuel planning.  So I began thinking through the system.  One thing that did not occur to me until much later is why I had to move the little lever by the gear handle to get it to retract.  On the Gar Kenyon Malibu’s ( pre late 86 models previous to the installation of the Parker Hannifin system with electric flaps) there is a gear handle safety solenoid which helps prevent the inadvertent retraction of the gear when the squat switch is in the ground position.  On the Malibu Mirage the sytemsis different, so the gear would not have retracted at all. The reason was that the squat switch was frozen in the ground position, and this is exactly the same reason I could not pressurize.

Now I was at a crossroads, if I could not pressurize I really did not feel comfortable continuing on the flight.  The thought dawned on me (I must admit that the schematic was not popping up in my mind as an indelible picture) what would happen if I took the squat switch out of the loop. Well only one way to find out exactly what would happen.  I pulled the gear warning circuit breaker and of course the safety valve closed and the cabin began to pressurize (albeit at an uncomfortable rate).  So now I had pressurized the airplane and I could continue.  Two things HAD to happen before landing. I had to depressurize the cabin, and also the gear warning circuit breaker needed to be reset so that I actually had a gear warning system.  Since I was cruising at FL190 that would give me a cabin altitude of 4,000 ft I would leave the pressurization controller set where it was which would allow the airplane to be completely depressurized slightly above 4,000 feet MSL.  Upon reaching 0 PSID on the pressurization gauge I simply reset the gear warning circuit breaker and everything was back to normal.

The point of this whole story was to say that had I not had a fairly good idea of how the system worked (gear warning/pressurization) I would have probably had to abort the flight and spend time on the ground waiting to resolve the simple problem. It was my systems knowledge that allowed me to safely complete the flight.  The knowledge of aircraft systems can and will assist you in being a better pilot and manager of the maintenance of your aircraft.

 

 

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