Jake@BevanAviation

Did you transfer the top and bottom board modules from your original unit to the new as removed unit?

@PT20J you are 100% correct. The autopilot system uses multiple boxes to process the incoming information and send the commands for correction out the the servos to control the aircraft. The flight computer (KC192) takes in information from the AI, HSI and primary navigator. Sums all this information together and produces a correction drive for the servos. The FD is a function of the autopilot flight computer. It gives a visual indication on the AI of what the system is trying to do based on the information it is given. The FD bars should always mimic the servo drive. If you ever have separation in the FD bars vs what the aircraft is doing with the autopilot engaged, you have a problem within the system.

FD drive always comes from the flight computer (legacy systems).

@PhateX1337My initial thought is some communication problem with the EA100, see print below. Ideally if the PFD has fully booted, then you turn on the radio master, the EA100 should communicate with the EFD, if the information is correct the ACU should tell the EA100 to extinguish the A/P AHRS fail annunciation. It's not uncommon to hear about EA100 failures. When they do fail you will have the A/P AHRS fail annunciation constantly and the A/P will not be able to engage. Aspen requires that their Ethernet cable be used for communication between the EA100 and the EFD and terminated correctly, if the required cable is not terminated correctly it can cause interference issues with the EA100 per the IM.

You have to keep the the KI256 for the attitude information, The G5 AI can not provide attitude information for the system but a GI275 can. The G5 and GAD29B will only provide GPSS, heading and course errors to the flight computer. Lateral and vertical deflection has to come from the primary navigator to the flight computer. Also, don't forget the compass valid (ground) to the flight computer. Without the compass valid you will not be able to select any lateral modes with the flight computer engaged.

@MoonFlyer68 If you want to give me a call on Monday we can discuss the details on the issue in the aircraft. Ideally there should be no change in the signal generation with a Garmin unit vs Avidyne. They should both follow the standard deviation signal of around 30mvDC per dot.

Unfortunately, with the current state of Century Flight Systems getting a Century 41 fully operational and reliable might be a big issue. A lot of the parts are no longer available for this system. Century is no longer doing repairs at the factory to my knowledge and has very limited support. Due to this reason I stopped working on the C41 years ago and would only send the system back to the factory for repair. The last system I sent in years ago came back with a 9K estimate for repair. My recommendation would be to replace it when you can for better reliability and support with a newer modern AP system like Garmin. There still might be some shops out there trying to do bench repairs but parts will be the biggest limitation. Altitude transducer problems were not uncommon for this system.

The G5 via the GAD29B can only provide heading or course errors to legacy autopilot systems. The vertical and lateral deflection (analog) must come from the primary navigator to the flight computer. When trying to couple the ILS or GPS approach the A/P system must be in approach mode with full up deflection on the vertical. The system has an anticipation circuit for the G/S capture that will monitor the closure rate of the vertical deviation signal and anticipate the capture. You can use GPSS to navigate to the fix, but you must turn it off and activate approach mode if you want to capture the vertical.

If in just attitude mode, with heading not selected and the system has the roll oscillation, with a level ADI. My first thought is tach gen feedback from the roll servo. If the compass system has not finished slaving the card will oscillate back and forth until it is slaved. During the slaving operation the compass valid output will be invalid, this should keep the AP from selecting heading mode. However, if someone has wired around the compass valid input to the flight computer you could select heading mode with the compass system still trying to slave and you would have a oscillation in flight. Once the system slaves the problem would go away. Something to look for during the oscillation would be is the heading flag on the HSI still in view? Best thing to try is see how the ap system does wings level without the compass system being used, so no heading mode just FD and AP on. If it still oscillates the compass system is not your problem.

We have seen some LED mods fail but it's pretty rare. For out of box failures BK has replaced the failed display but the process does take some time. If I had to guess for a manufacture warranty, possibly around 90 days. The display connector is prone to failure so that is a possibility or we have seen some of the contacts on the LED board cause issues. As for the website you linked, it's not a approved mod and we have never seen one in person but have had multiple inquires about it in the past. The only approved mod for the old gas display replacement is the LED mod.

My guess would be a display problem or possibly a display conductor strip problem. We do have new displays and the conductor strips available but if you want to send the units in we might need to order more conductor strips as we only have 3 in-stock and there are 2 per unit. You can give us a call at 316-946-4870 and ask for Thom or Mike. They are the techs that work on these units and would be able to answer any additional questions you might have. I did briefly talk to them about the issue and they said the display strips are a common problem and if you gently push on the display and the digits come back that might be the issue. Just be careful to not push to hard and break the display.

The manual list the lamps as 037-0032-09, there is a special lamp for the DH illumination of 037-0049-01. I do not work on any indicators and I would suggest to only have the indicator repaired at a appropriate rated instrument repair shop.

If you want to stay in the Dallas area you might reach out to Trevor at Tech Aero in Denton. He is an amazing tech and knows how to efficiently troubleshoot these legacy systems. You want to bring the aircraft up, just give us a call to make sure we have the room. If Trevor wants to remove the servo and cold soak it then check the voltage regulation that is where I would start.

The trim servo has a voltage regulator that generates a regulated voltage off the trim power. This voltage is used for MET (manual electric trim) and is monitored by the flight computer in the event the regulator fails to annunciate a trim failure condition. It is possible that in the colder temps the voltage is just out of mfg. specs for the monitor circuit in the computer. As the components warm up, the voltage falls within specs and the failure warning on pft goes away. If the regulator fails and goes INOP you have no MET functions and a constant warning from the flight computer. I would be curious to see where the regulated voltage was when the unit was cold. There is a zener diode in the trim servo that could be replaced to increase the regulation in cold temps if it is too low. During PFT, the computer sends two up drive pulses and two down drive pulses to the trim servo and monitors the feedback lines to see if the motor is functioning. If you are getting the 4 trim light flashes during PFT we can assume the computer is sending the commands to the servo and looking for feedback. If for some reason the motor does not run the system will fail the PFT. During this test the solenoid will not pull so you won't see the trim move in the aircraft.

@jaylw314 It can be repaired, typically we send the sticking needle issues to Mid-Continent instruments for repair.

It's not uncommon to have the G/S pointer stick on the KI-525. If the pointer gets stuck you can take the palm of your hand and bump the panel around the instrument. After bumping the panel they will drop into view and respond correctly until it gets stuck again. Only way to really fix this is have a instrument shop open the indicator up and clean/repair the G/S pointer assembly.

@goodyFAB The main problem with the Century 41 system is that Century is no longer supplying parts for the majority of the assemblies. This applies to all legacy systems they produced. Without the correct parts repairs will be extremely limited. The last discussion I had with the owner of Century Flight System they stated that they were no longer doing repairs at the factory. The Century 41 flight computer is full of ribbon cables that delaminate over time and cause major issues when trying to repair the unit. The last Century 41 I sent to Century for repair which had alot of ribbon cable issues and other board assembly issues came back with a 9k estimate for repair. This was a couple of years ago before they shut down factory repairs. I do have the test set and the manual for the Century 41 system but depending on the failure, parts might not be available. I would not be surprised to find delaminated ribbon cables inside the unit and I do not have any replacement cables for the Century 41. You can contact Autopilot Central and see what they say but they will have the same issue I have with parts unless they have a supply of new parts available. Century Flight Systems are in a pretty bad spot, with personnel retiring and no new trained techs for legacy systems available, no new products to market, it looks pretty dim for the future. What I tell any customer that has a Century 21, 31, 41 or 2000 is if the system is still working keep it going, but start saving for a future upgrade as part availability will severely limit the systems ability to be repaired and supported.

@pkofman I have not personally seen an instance where a failed KAS-297B would cause the KC19X flight computer to not pass PFT. The alt pre-selector was an optional system that could be added to the KFC150 system. It does get information from the flight computer system for oscillator and digital data. There is the possibility that if the unit were pulling the oscillator low that it could cause the flight computer to fail a PFT. If you wanted to isolate the KAS-297B out, I would just unplug the unit and then try the PFT on the flight computer. I would not be surprised if the flight computer you have has capacitor leakage in the power supply circuit. This is a known issue with units manufacture from 1993-1998. Are you getting the 12-13 flashes of AP on a successful completion of the PFT? Also, when the unit fails the PFT do you get the flashing trim fail annunciation or is the unit completely dark?

The KC19X is the model number of the flight computer. KC190 is a KAP100 flight computer. KC191 is a KAP150 flight computer. KC192 is a KFC150 flight computer. The individual part numbers of the flight computer will differ from model to model and are voltage specific.

King part numbers are 037-00032-0010 for 28v lamps 037-00032-0008 for 14v lamps

We do not work on the KAS-297B. I would suggest Mid-Continent Instruments, Duncan Aviation, or Southeast Aerospace for evaluation/repair. To my knowledge the only box that works in place of the KAS-297B is a GAD43e that is paired with the G500/600 glass displays.

To replace the lamps in the KC19X unit, the bezel has to be removed. To do this, the unit has to be opened up. Some of the screws are only accessed from the inside of the unit. Whoever replaces the lamps in the flight computer make sure they are spaced properly, if they are too close to the lens it can burn it over time. We do not work on the alt pre-selector (KAS-297B).

@WaynePierce 12-13 flashes of the AP light should indicate a pass. If the compass valid is inop on the GI275 it will not allow you to select any lateral guidance mode. Basic roll only mode should still work for wings level. On the side of the unit should be a red 4 digit stamp. Typically it is on the back of the unit around the transducer static port. For example 4685 would be the 46 week of 1985. Units made from 1993-1998 have capacitor leakage problems. This can cause issues with the unit passing PFT or allowing it to engage. There is also a current sense resistor in the computer that has very tight tolerance, if it falls out of tolerance it can cause issues with intermittent disconnects. Any time I get a KC19X unit in for repair I always replace the current sense resistor as preventive maintenance. Thom Duncan Avionics in Fayetteville is pretty sharp on the KAP/KFC150 system. If you need a shop to troubleshoot the aircraft that would be my suggestion. Another option would be a loaner unit, I might have something available but I would need to know what your dash number is. If you have any questions or concerns just give me a call.

@WaynePierce if you are able to get a video of the PFT sequence that would be very helpful.

For the KAP 140 when changing from a DG to HSI they have to be reprogrammed via a laptop. The KAP/KFC150 has sealed resistor modules that can not be re-strapped. They are specific for the air-frame installation and the flight computer options (FD or no FD, DG or HSI). If you went from a DG to a HSI the top resistor module would have to be changed. Any time you change the attitude source you have realign the flight computer to the new attitude source. This is even mentioned in the installation manual for the GI275. When you were doing the PFT test in flight did you get the proper sequencing of lights (4 flashes of trim, 12-13 flashes of AP)? If you did not get the sequence listed below there is something missing that the computer wants during PFT. Things that could cause a disconnect in flight are listed below. Faulty disconnect switch Faulty return springs in the MET switch assembly not returning the switches to center. Faulty gyro valid relay in the GI275 Activation of MET (manual electric trim) switch with the AP on Failure of the power supply monitor circuit in the KC191 Loss of compass valid from the GI275