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.


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.





Operating a Cessna 421 LOP

After the purchase of a Cessna 421C in 2005 on of the first mods we performed on the aircraft was the installation of the Micro Aerodynamics VG kit.  We wanted to obtain an additional margin of safety provided by the lower Vmc speed, but we also liked the additional 130 lbs of useful load.  Weight carrying capacity was a primary reason for choosing the Cessna 421 to begin with, so any thing that could be done to increase weight carrying capability and increase range was something that interested us. We frequently were carrying five to six passengers in addition to me at the controls.  The power settings we were using in the 421 were burning 22GPH per side and getting a bit over 200 KTAS.  There are few aircraft that could do this (other than a turboprop) and ,  I wondered if there was something we could do to increase the range especially on the “heavy” trips. We departed at max gross weight on about 90% of our trips.  Most of our trips consisted of carrying maximum passenger loads while carrying a safe amount of fuel (rather than topping off).  Incidentally it was these trips that made me realize that in most cases it is best to carry enough fuel to complete a trip with a safe reserve.  Less fuel means less weight. Less weight means a faster TAS. Plus an added benefit is that at lighter weights you will experience lower CHT’s because of increased airspeed and faster climb speeds for a given climb rate.

It was about this same time that I began flying a PA46-310P Malibu with a TSIO-520BE engine. I was not inclined to use LOP operations, but quickly found that this aircraft not only could run LOP very well, but really needed to in order to haul a decent load and keep engine temperatures in check.  This engine and airframe were mated for the singular reason of being able to run on the lean side of peak.  In the mid eighties when the Malibu was introduced few airplanes had multi probe CHT/EGT indicators.  Piper did introduce the Malibu with a single TIT indicator which while rudimentary was actually quite accurate.  In 1984 few people understood the science behind LOP operations, and many people refused to accept the fact that leaner mixture meant cooler temperatures.  In addition to these misconceptions fuel was cheap and a few extra gallons would not hurt the pocketbook all that much.   It was my operational experience in the Malibu that led me to realize that the 421C would be an excellent candidate for LOP operations.

GTSIO-520Take a look at the TSIO-520BE (PA46-310P Malibu Engine) , TSIO-550 Engine, or GTSIO-520L&N engine and you will quickly realize that there is a fair amount of commonality especially in regards to the induction systems, and the top end (cylinders and valve train). They all have a similar style of induction system which enables these engines to have an even air/fuel distribution. This style of induction system lends itself well for LOP operations. These engines also have the cross flow cylinders with the overhead inclined valve train.


In some cases the GTSIO will run well LOP with stock Continental injectors, but I tend to think that this is not the norm.  In order to get the best performance, CHT’s and smooth operations most aircraft will need to operate on a balanced set of injectors to get smooth engine operation.  This will normally involve purchasing a set of balanced fuel injectors from the well know General Aviation Modification Incorporated commonly known as GAMI.  My project began by ordering two sets of fuel injectors from GAMI.  As many may already know the injectors which you receive are normally all one letter for example “E”.  This letter refers to the orifice size of the fuel injectors.  Change the size of the orifice and you change the amount of fuel flow to the cylinder.  More fuel flow means the cylinder will peak later (in comparison to other cylinders), while a smaller orifice means that the cylinder will peak sooner (in comparison to other cylinders).  Ideally with a well tuned engine all cylinders peak within a range of .3 GPH.  The idea is that during the leaning process the first cylinder peaks and the last cylinder peaks with .3 GPH of leaning.   By having the variable orifice sizes this compensates for uneven fuel/air distribution which is present in virtually every internal combustion engine.


Once the injectors are installed the process of fine tuning the injectors to an individual engine begins with a GAMI lean test. The lean test involves recording EGT temps versus Fuel Flow.  I personally like to perform the lean test at about 10-12,000 ft. MSL.  The reason for choosing this altitude is twofold.  First this altitude is above nearly all of the traffic (in our area of East TN), and second this is low enough that a slow leaning process will not cause any high CHT problems as the 50 ROP to Peak EGT/TIT realm is traversed.  I recommend a clipboard and two printed copies of GAMI’s lean test paperwork.  The values could also be downloaded from any number of the Graphic Engine Monitors to an excel spreadsheet. These numbers will determine whether the each individual cylinder needs a leaner or richer injector.  After reaching 10,000 ft MSL I begin the process of leaning.  I normally set cruise power at 30” and 1800 RPM (engine is turning 2400 RPM).  The pull begins by pulling the mixture all the way back to 25GPH.  After leaning below 25GPH the temps begin to rise substantially.  It is important to lean steadily,Cessna 421C Throttle Quadrant precisely, and at a pace that will prevent CHT’s from rising out of control.   If you lean too rapidly it will be difficult to identify peak EGT and the engine monitor may not indicate correctly.  If you lean too slowly you may end up pushing your CHT’s up over 400°F. A note here is that once you know what TIT/EGT at which your engine peaks it will be fairly consistent when flying at normal altitudes.   For a given power setting you will be able to pull back to a given fuel flow and you will be very close to your LOP setting. One thing you will discover when leaning a Cessna Twin (or any twin for that matter) to lean of peak is that you must develop a precise control of the mixture in order to do it well.  I found the placing my index finger on the mixture knob, and then placing my thumb in the groove where the mixture control rides provided tactile feedback to indicate when I made the slightest movement of the mixture.  Those cables are quite long and the change will take a few seconds, so if you are trying to lean at .1 or .2 GPH rate you must be very PATIENT.  Move the mixture a bit and wait about 15-20 seconds and see if the fuel flow changes.  Continue this process until you get all cylinders to peak recording the results.  It is good to take an assistant along who can assist in looking for traffic and recording data.

Insight GEM 1200 Engine MonitorIf you want to fly your Cessna 421 LOP, or C340, C414, or virtually any of the piston singles or twin aircraft I think the best way to do it properly and safely is to have the right engine instrumentation.  I firmly believe that in order to do this it is best to have some type of Graphic Engine Monitor which indicates CHT/EGT for all cylinders along with a TIT readout.  In addition to this it really helps to have a digital indication of fuel flow down to the tenth of a gallon.  The digital FF readout is very important when performing the lean tests.  When leaning for cruise it gives a measurable way of reducing fuel flow in a minute amount.

In order to get our Cessna 421C to purr along at LOP mixture settings we needed to do a few minor “tune up” items.  First of all I recommend that anyone attempting to run any Teledyne Continental Engine LOP, that you begin by performing TCM Service Information Directive 97-3E.  This SID involves setting fuel pressures along with idle mixture settings.  Making sure that these setting are in line will assist in smooth LOP operation.  It is also very important that there are no induction leaks.  Induction leaks may be tracked by pressurizing the intake system and using soap bubbles to identify any leaks.  In addition to these items it is essential that the ignition system be in top condition and that the engine timing be set properly.

Now to the results and benefits of getting the Cessna 421C running LOP.  Immediately after getting the airplane configured and running well LOP I went to the AUX pages in the GNS 530 and reset the Trip Statistics, so that I could track the changes in average Ground Speed (I left the GNS 430 the same for comparison).  After several months of flying we had some data to compare.  Operating ROP I used 30” and 1800 RPM we truing out in the low 200 KTAS range while burning about 44-45 GPH depending on OAT and CHT.  After some time spent flying LOP we discovered that we were getting about 195 KTAS, and burning 35-36 GPH.  That computes to about a 20% reduction in fuel burn with a 2.5% reduction in KTAS.  This translated into a much greater range.  One of our trips which changed dramatically was at flight to the MYNN (Nassau, Bahamas).  Instead of needing to stop at Fort Pierce and take on fuel we could go to CRG (Craig VOR), and then go straight down to MYNN.  We would normally land with about 50 gallons after the flight.  There were also several trips which without the range increase from operating LOP would not have been possible without a stop, but now were easily within reach.   This may have contributed to the average ground speed being closer to ROP operations than expected.  We were staying in cruise longer which meant less time in climb, descent, approach, and landing.


These range charts comes from my experience flying the Cessna 421C. I planned for 55 Gallons of fuel burn the first hour (both ROP&LOP).  The successive hours I planned at a fuel burn of 45 GPH ROP and 36 GPH LOP.  The range numbers I derived from the average GS obtained from the GNS 530.  The average GS in the 430/530 is calculated from when the takeoff to landing.  Our ROP average GS was 183 Knots, while the LOP GS only dropped 3 knots to 180 Knots.  Based on these average ground speeds I calculated the above ranges based on the three main fuel capacities found in the 421C model.  These numbers take into consideration a one hour reserve at cruise fuel flow.

Lean Of Peak Chart One

 Lean Of Peak Chart Two

The other benefits are quite typical for aircraft which are operated LOP, and included lower CHT temps, cleaner oil, better oil samples, better cylinder life, and overall better engine service.  It is not all that atypical to put a set of cylinders on a GTSIO about every 600 hours.  We were able to fly all the way to 1400 SMOH before we had to look at any cylinder work.

A couple of limiting factors for LOP operations which I have discovered in pressurized piston aircraft at higher altitudes may affect the maximum altitude at which LOP operations will work well. Many Twin Cessna pressurized aircraft have been modified with pressurized magnetos.  This is an essential element if you want to run LOP at higher altitude. I have also found that at above about FL200 and FL210 the wastegates are closed or nearly closed all the way with cruise power settings.  With the turbos providing nearly all the “boost” they are able to there is not any buffer.  With no buffer any change in pitch or airspeed the MAP will vary a little bit.  These engines just do not seem as smooth LOP above these altitudes.  The engine is in a sort of “coffin corner”.  Due to the higher altitude and more compression of the air from the turbos the induction air is hotter and therefore the CHT’s are hotter than lower altitudes.  In order to keep the engine running cool enough while operating LOP it requires a leaner mixture.  At the higher altitudes (above FL210) this leaner mixture results in a little engine roughness.  It varies a bit from engine to engine, but certainly at the higher altitudes it is a factor.

If you have been contemplating operating your Twin Cessna on the “Lean Side” feel  free to contact me for more info at (423)647-4359 or dmoo@flighttrainonline.com or check out my website www.FlightTrainOnline.com.  Watauga Flight Service provides initial and recurrent training.  We provide initial & recurrent training in Cessna 335, Cessna 340, Cessna 414, Cessna 421, Cessna 425 (Conquest I).  In addition to this we also provide training in Piper PA46, Malibu, Mirage, Meridian, JetProp, Matrix, King Air 90, King Air 200, Beechcraft Baron 55, Baron 58, Baron 58P, and Cessna 210 (T210, P210).





Checklist or Do List

Checklist or Do List

Fly with any number of pilots and you begin to realize that checklist usage varies dramatically. For the sake of this discussion we will only deal with single pilot operations.  On one end of the spectrum is the pilot who claims to have his checklist “memorized”, while on the other end of the spectrum you have the pilot who reads each item and then performs the items.  This brings several questions to mind.  Which method is more accurate? Which method is more efficient?  Which method lends best to a single pilot IFR environment?

Webster says a checklist is a list of items, as names or tasks, for comparison, verification, or other checking purposes.  It is my belief that the key word in that definition is verification.  When you look at the two aforementioned pilots the memory pilot knows the items well and performs the items, but did not verify that all items were completed.  The second pilot simply reads the items, not checking the items, but rather performing the items as a do list.  Both pilots run the risk of missing crucial items.  One is relying only on memory, while the other is relies only his ability to follow the list point by point despite distractions. The best method in my opinion lies somewhere in between the two methods, a sort of compromise between not even looking at the checklist and reading it item by item.

The word “flow” has become somewhat of an aviation buzz word.  A “checklist flow” is a way of proceeding through any number of items in an orderly manner based on the physical location of the items in the aircraft.  With an aircraft that has most of its switches on the left (twin Cessna) you might start on the left and move to the right ending up at the fuel selector.  In many Cessna singles you may start at the fuel selector move up the center pedestal and then over to the left side of the panel.  In the later Piper Malibu Mirage, Matrix, and Meridian most of the switches are in the overhead panel, you may begin working from there down.  The point is that you need a logical starting point and stopping point which will pass by items related to the checklist that you can complete in a fashion so as to not miss anything.  After this flow is complete, now is the time to consult the checklist paper or electronic.  I have found over the last 10 years of flying that the electronic checklists are fundamentally a much better and more efficient way of completing checklists.  It is almost like having another pilot to reading them aloud.

My first introduction to the use of electronic checklists was in the King Air 200.  We had a Primus radar with a built-in electronic checklist.  The checklist items could be advanced via a selector on the lower center pedestal, and a switch on the yoke.  This is far more efficient for a number of reasons.   The first reason is that you never lose your place as happens with a paper checklist.  When an item is checked electronically the checklist moves to the next item and shows which item is next.  Here is a scenario which happens often in flight.  You are reading down through the paper checklist when ATC calls with a frequency change, so you stop, tune the frequency, check in with new ATC controller, and then return to the paper checklist.   Now you must reread several items to find your place again before you resume your checklist.  This all takes time at the crucial point of a flight where the workload is the greatest.  Using your electronic checklist allows you to go back to the exact point you stopped.

Garmin has been a leader in the area of electronic (well up until the touch screen units came out).  In 1994 when Garmin introduced the GPS155 which was the first approach certified panel mount GPS it had a checklist function built into it.  Garmin continued this with later panel mounted units including the ubiquitous GNS 430/530 models.  Even the portable 696 unit and the newer 796 models have the checklist function available.  For some reason Garmin must have not seen the usefulness of their built in checklist and as a result the 650/750 models do not have the software.  Don’t lose heart however as there a number of electronic checklists available.  See the You Tube video of my utilizing the checklist function on the Garmin 430.



Since the iPad and iPhone have found their way into the cockpit in great numbers pilots now have an easy avenue for the use of electronic checklist.  There are at least a dozen or two iPad and iPhone apps for electronic checklist, so there are no shortage of apps.  Personally I have Foreflight on my iPhone as a back up to my other Electronic Flight Bag (EFB) software, so I am somewhat partial to their apps.  The picture below is a screenshot from my iPhone using the Foreflight checklist lite.

My main EFB software which I use for charts, XM interface, and a multitude of other flight related tasks is FlighPrep Chartcase Professional.  Part of their software is a checklist interface.   I have used this interface and it has worked well for me.  See the picture below for an idea of what their electronic checklist looks like.  I currently run their software on a HP Slate 500 tablet.

Whether you want to continue using the old faithful paper checklist, or you like me are using an, electronic checklist, I encourage you to analyze how you are completing your checklist.  Are you performing the items and then returning to the checklist for verification, or is the checklist little more than a do list that you roam aimlessly through?  Consider sitting in your aircraft(s) and writing down a flow pattern that you can memorize and then verify completion with the checklist.  You will be surprised how much easier, more accurate, and more efficient this method is.




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.



Turbo Failure (Land as Soon as Possible)

Turbo Failure 

In the process of initial and recurrent training I always try to talk about turbocharger failures and what that means as a whole.  It has been a common question posed by clients during initial and recurrent training in piston engine turbocharged airplanes.  One common question is how the engine reacts when I lose one turbo (assuming that they have twin turbos).  In relaying my turbo failure incident from a couple of summers ago, hopefully I can shed some light on this emergency.  Yes I did use the word emergency and I will explain why later.

The day started much like many other days in my flying career.  It was a fairly early morning departure from our airport in July a somewhat hazy day, but overall decent weather.  Our first stop for the day was to be Atlanta Hartsfield Airport to pick up a passenger who was arriving on the airlines.  Because the temperature had dropped that evening and the high humidity/dew point there was some fog at ATL, but as the sun came up I expected it to burn off rather quickly.  From our airport to ATL we normally get routed over the Foothills VOR (ODF) V222 LOGEN then direct.  It was a typical morning, but due to the fact that we were out flying early we got a little gift from ATC and were cleared direct to LOGEN.  We ended up on the ILS because the fog had not cleared yet, but the ceiling was improving as was the visibility.  No problem getting into ATL other than the typical request from ATC to keep the speed up followed shortly thereafter by the request to slow down.

After picking up our passenger at ATL we departed for Thomaston, GA.  OPN.  The weather was not improving quite as quickly at OPN so it would require an instrument approach.  The ILS was available so I set up and flew my second ILS of the day.  Landed with no problem.  In  fact I got a little surprise on roll out when I was the DC-3 that I had worked on and recovered the controls for about 10 years earlier.

A few hours later we depart for the reverse of what we had flown earlier.  A return flight to ATL and drop off and then a flight back to our home base in Elizabethton, TN.  Normally the return trip out of ATL goes something likes this: NELLO, HRS, SOT HMV.  This route takes me over the heart of the Smokies, but today it would be different.  There were a number of thunderstorms building over that route which would require a route further north toward Knoxville.  After getting to the vicinity of Harris VOR I took a more northerly heading toward Knoxville.  By the time I had flown just slightly past Knoxville at 17,000 FT. I started my turn back towards 0a9.  At this point I had cleared most all of the weather and would have a pretty direct flight back to home, and now I had a descent tailwind and my ground speed had increased.  Sometime after passing Knoxville I felt something in my ears.  What was that?  Looking at the pressurization I realized that I was depressurizing.  Check the dump switch and it was where it needed to be.  At this point I could feel the airplane slowing and I looked at MAP gauge.  I am only making about 13″ MAP.  I have a definite problem and need to start a descent.  My request went like this, “Atlanta, 75P we are depressurizing and need to start a descent down to one zero thousand.”  ATC replies, “Ok 75P turn 20 left you have traffic.”.  I guess they did not understand me so I replied, “NO! I am leaving one seven thousand for one zero thousand NOW!”  They reply, “OK, so and so airplane turn right 40 degrees.”  My thoughts then were why did he not do that in the first place, but Oh well I am descending now.  It was not a big panic situation with the aircraft being only at 17,000 ft I was not going to pass out or lose my ability to make decisions for several minutes.  I am making a fairly normal descent of 1,000 FPM to 10,0000 ft.

Upon reaching 10,000 ft. my MAP had risen some which told me that I had a problem in keeping the intake manifold pressurized enough to maintain the 30″ MAP setting I had been cruising at.  I begin the mental process of deforming my next action.  Should I land immediately?  By all indications the engine is running smoothly albeit at a much lower power setting.  During the descent from 17,000 ft. to 10,000 ft I have chewed up a fair amount of real estate between me and my destination and I am showing about 15 minutes out.  I decide that 15 minutes won’t be that bad and I have to lose the 10,000 ft of altitude anyway so by the time I do that in a straight line I be very close to my destination.  I am now handed off to Tri-City Approach the facility that controls the airspace around my destination.  I opt to stay at 10,000 ft rather than descend just in case I have a problem.  A minute or two later I pass Greeneville, TN which is one of the last airports before my destination.  Shortly after passing this airport I notice a twitch in the oil pressure needle.  The OP is dropping.  I inform my passenger of what is going on and now I am getting lined up on about a 10 mile final for RWY 23 but I am at 7,000 ft.  I want to keep as much speed as possible in case I have an engine failure, so I do not lower the gear at this point.  I am descending at a pretty rapid rate and indicating around 185 KIAS.  I get to a point where I know I am going to make the runway and I slow and lower gear.  As I am landing the OIL PRESS annunciator is on and the gauge is nearing the bottom.  As the wheels touch I pull the mixture and roll into the FBO ramp.

After rolling to a stop we safely exit the aircraft, and I begin my inspection of the aircraft.  I am sure that I am going to see oil coming from somewhere, dripping, oozing, or spilling from somewhere underneath the cowling, but there is not sign of oil anywhere.  I decide to check the dipstick, and guess what there is no oil on the dipstick either.  At this point it becomes very clear to me where the oil went and what happened that caused me to lose pressurization.  It must have been a failure of pressure fed bearing in the turbocharger.  When the bearing failed the oil must have been burning as it left the exhaust.  I do see that the left exhaust is a good bit blacker than the right side.  Indeed I had lost the left hand turbocharger.  I wonder if it looked like an airshow with the smoke on as I burned nearly 8 quarts of oil through the exhaust in about 10 minutes of flying.

What do I take with me from this situation?  I have communicated this several times to my clients since then that if you have a suspected turbo failure the procedure to follow are to land as soon as possible.  In my mind at the time I was trouble shooting all the possible failures.  It could be an exhaust system failure (without proper exhaust back pressure there is nothing to spin the turbos).  It could have been a controller issue or perhaps a wastegate issue.  Without knowing though I should have assumed the worst and made an immediate landing.  Fortunately for me having taken a more northerly route on this trip I was in a position where I was much closer to several airports.  Because of the nature of turbocharger failures it is imperative to treat it like a serious emergency.  Don’t hesitate to land at the nearest airport it may save you and the aircraft.


Hyper Smash