Jake@BevanAviation

@0TreeLemur I am pretty sure we have new knobs available. Give us a call Monday and ask for Mike, he should be able to give you a rough idea of what the repair cost would be.

Slow erection or excessive noise from the indicator are always signs that the bearings are worn and eventually the rotor speed will be to slow to maintain rigidity. Try to make note of the gyro orientation as the gyro is spooling up, a fresh overhaul always has a nice shake out of the indicator as the rotor speed is increasing. When the bearings get old and stiff you will see a reduced shake out or none. If you witness the AI no longer shaking out during the initial start of the aircraft, that is a sign that the indicator is getting worn. Always replace the filter when replacing the AI.

@VA FLYER I would assume someone would have to get approval from Castleberry if it was still under warranty to try and repair the issue. The instance I had was the AI would intermittently loose the roll output signal. I removed the AI from the aircraft and put it on the bench, gave it some excitation for the outputs to work, put it in a constant bank around 10 deg and monitored the output. Without influencing the AI I could see the signal drop out and come back after some time. This was in a Duke with a Century 4 and a replacement electric Castleberry AI for the Century 4 system. A shop in Florida had spent months trying to figure out the issue but with it being intermittent some flights were great, other not so much. The main issue was randomly it would start a oscillation chasing the heading bug but the longer the oscillation went the more drastic the banks would get. As the oscillation continued the aircraft would be doing large s-turns chasing the heading bug at a very aggressive bank. When the AI signal came back it would stop and track the heading like normal. If this sounds close to what you are experiencing I would suggest to have the AI put on a bench and have it double checked for intermittent outputs. This can also be done in the aircraft but it won't be easy. If you need a shop to help troubleshoot this issue I would suggest talking to Jason at Freedom Aviation in Lynchburg VA. I have been working with Jason for years helping them troubleshoot autopilot issues. If you want to chat about the issue just give me a call.

@VA FLYER I have seen a couple of Castleberry electric replacement AI's have issues with solder joints that have caused this same behavior. If it was me I would be checking the AI on the bench and looking at the output. The FD bars are a representation of what the flight computer is commanding.

If the aircraft is banking more than the standard rate turns (approximately 20-22deg bank), that sounds more like a AI issue. When this happens if you tell it to turn right 90 deg it will continue to turn right until you tell it to stop, they are overly aggressive in commands due to the missing information from the AI to limit the response of the autopilot. If you don't tell the system to stop turning, they will turn over on itself.

Most of our quotes were in the 22-28k range depending on options.

@Sue Bon The very early Century IIb units that specifically had the square white push button switches had griplet boards. The griplets connected traces from the top of the board to the bottom of the board and have a history of being intermittent and a pain to troubleshoot. Also, the white push button switch had contacts that were prone to spreading over time that would cause intermittent signals. When the system looses the heading error voltage, it will default to the roll centering pot. If the roll centering pot happens to be set for left roll, that would be the direction the system would drive if it lost the heading error. When you turn heading mode off, it defaults to the roll turn knob and the roll centering pot for correction commands. Later revisions of the Century IIb changed to through-hole circuit traces and did away with the griplets. They also change the push button switch to a white rocker switch that controlled a micro switch to provide the heading error to the system. A very common issue with any legacy Century system is the blue amphenol female split pin connector, it has a history of being intermittent. They used this connector on a variety of different components.

@N201MKTurbo The Century 21 has no roll knob function. This was a feature in older Century systems. Depending on where the bank angle is set for the individual system, 30 deg bank is very close to the limit of the system. Heading errors typically default to the around 20 deg limit for most legacy systems (book spec for the Century 21 is around 24 deg). This can vary based on where the limit pots are set for the aircraft. For the example given of 30 deg right bank, that is beyond the 24 deg heading limit (book spec). In theory, when it is beyond the max bank limit no amount of right heading bug error would allow the unit to continue to drive to the right. A good rule of thumb is when possible always try to null the AI when doing ground testing or simply unplug the AI for ground test. When you unplug the AI the computer thinks it is getting nulled information back from the AI. If the circuity is working properly you should be able to fully control the system on the ground. Just don't forget to plug the AI back into the system or you will have a very interesting ride.

My guess is part of the drive circuitry for the roll servo is faulty resulting in only drive in one direction. Possibly a set of faulty drive transistors. First try reseating the unit in the rack and see if that resolves the issue. If the issue is intermittent it could be a issue with the flight computer, roll servo or possible wiring. Additional troubleshooting would be needed to isolate the problem. If you are doing ground testing make sure the AI is spooled up and as close to level as possible. If the AI is laid over the system will try and drive the servo to correct the laid over orientation of the AI. For example, if the AI is laid over 30 deg to the right indicating a right bank, the system will want to drive to the left to return to wings level with the heading bug under the lubber and heading mode selected. Heading drive will be limited in this scenario, you would be able to drive left but very limited drive to the right if any.

KA-185 is used with the KAP/KFC150 system. It uses binary bit information from the KC-19X to control lamp annunciations. KA-285 is used with the KFC 200 system. It uses logic lows provided by the KC295 to control lamp annunciations. Units are not interchangeable.

Trim boards are inside the C2000 flight computer. If you remove the flight computer, take the top cover off and the trim board is the top left board. Look and see if you find any visible damage to the board. It is not uncommon to see the drive transistors go bad and burn the motherboard.

@MoonFlyer68The S-Tec flight computer would have to be converted to the ST-901, and the ST-901 would have to be set to what ever compass system you are trying to use. In theory if the ST-901 had the appropriate connections to the GPS navigator, it should be able to provide the simulated heading error to the flight computer.

@Glen Davis I sent you a pm on something you could possibly try to narrow it down. Also, if you can get a video of the oscillation that might give me some clues on the possible issue.

@M20R I would have expected the value to be closer to a null. Might be worth a look at the sensor inside the pitch servo.

@M20R What was the value of the trim sense in the analog inputs screen? It is not uncommon for the strain gauge in the pitch servo to get covered in dirt, grim, and get stuck causing the aircraft to auto trim more than needed. Are you getting any audible messages of check pitch trim? Also, in the analog outputs screen you can command the servos to run to see if you have a servo drive issue.

Best way to start troubleshooting the KFC225 system is to pull the error codes via the diagnostic port with a special cable and laptop. Find a shop that has this ability and have them pull the codes. In the flight line maintenance manual is all the error codes and the meaning. That should isolate the issue down to a individual component. Normally the problem is not the computer, it is some other component in the system. For repair you are going to be limited to Mid-Continent Instruments, Duncan Aviation and South-East Aerospace for bench repair. Honeywell changed the dealer service agreement years ago and limited the service on KAP140 and the KFC 225. You might reach out to Paul at Bragg Avionics in Jacksonville , they might have the capabilities to pull the error codes.

@PeteMc The aircraft that was referenced was worked on June last year. Last email I have from the owner was January this year when it was working correctly after multiple cross country flights.

@drb930 Had a customer with a A36 KFC200 and Aspen 1000 with the EA100 that had similar issues. He ended up getting 5 different EA100s before getting the system to work correctly. The final EA100 came out of one of Aspens aircraft that had a good known working history. Powers and grounds were replaced, the Ethernet cable was replaced, shielding was checked and the failure always happened on long cross country flights. A couple of units failed completely random even had a DOA with one unit. There is a thread on Beechtalk link that goes over the issues.

If you can't get the racks out due to the rivets the other method is to remove the back-plate and connectors to the desired GNS unit. You might have to undo several connectors from the back-plate if the bundle is tight to gain access. If you have large hands this can be a royal pain but doable.

#1 all Century systems use a brushed DC drive motor, over time the carbon brushes will wear and create a carbon dust. This dust can cause the back bearing to get stiff, when the bearings get stiff it takes more drive voltage from the amplifier to get the motor to run. A good clean motor with new bearings and brushes is typically around 800mvdc for start up. The amplifier provides the drive voltage and the motor moves the control surface in the aircraft. If the servo is bad, repairing the amplifier or swapping will not resolve a high start-up voltage in the servo. You can try and run the servo at max drive voltage (12VDC) for a long period of time to try and free up the bearings but this is only a temporary fix. As long as the brush cap is full of carbon dust the bearings will get stiff again just a matter of time. #2 If the TC has the pin-out placard on it as most do I would suggest try to run it on a bench. A good tech should be able to decide if the gyro is spooling under power or if the rotor speed is to slow causing the flag to be in view. Pin out of Century 1,2,3, and 4 system servos are as follows. A= Solenoid power B= Solenoid ground C= Motor drive D= Motor drive All you need to check motor start-up voltage is a variable DC power supply. Applying power to C and ground on D will cause the motor to drive. You start at 0VDC and slowly turn the voltage up till you hear the motor start to run. Note the voltage and repeat the test 3 times in total and take the average. This average voltage should be under 2VDC max. If you are above 2VDC the motor needs to be cleaned and possibly new bearings and brushes. The Century II system is roll only, a Century III system is roll, pitch and would have alt hold. If you do have the IIB my guess is you have a additional box from a different manufacture that does alt hold, possibly S-Tec 30 alt or 60 PSS. S-Tec systems use brushed DC motors from Globe just like Century and are susceptible to start-up issues as well. They also rely on the pressure transducer to control alt hold functions and the old blue plastic ones are known for issues. Interconnect prints for some of the legacy systems are available for free on Century's website (https://www.centuryflight.com/). See Technical help / Drawings and Schematics.

With any legacy Century system servo start-up voltage is critical for proper tracking. The higher the start-up voltage gets the worse the performance is, typically poor tracking or oscillation in flight are associated with high start-up voltage. This can be easily checked in the field with a portable variable dc supply, power on pin C of the servo and ground on D. Turn the supply up until you hear the motor running and note the voltage, do this 3 times and take the average. It needs to be under 2VDC max, the higher the voltage the worse it will perform. They should also check cable tension and ensure there is no slack. Another thing to check would be the condition of the AI for the Century system as this is the backbone of the system. If the gyro is bad it will affect the performance of the system. On a good AI when the engine is started the AI will do a shake out as the gyro starts to spool. As the rotor speed increases the gyro the will start to stabilize and level out. If it does not shake out and is slow to erect you could have stiff gimbal bearings. Typically a flag in view is indication there is a problem with the associated instrument. Flags on a TC is normally from slow rotor speed. Most TC have a pin out placard on the instrument for the connector. Using a DC supply you can get them to run on the bench to see if they are noisy or if the gyro is even spinning under power.

@carusoam had a good discussion with the aircraft owner and the shop. Gave them some things to look at now that we know why the aircraft is trimming so much.

I would be curious to know what the course signal coming from the HSI was with the course pointer under the lubber line? Ideally it should be 0VDC if you were looking at it with a multi-meter. With a center lateral deflection (0mvdc) and a nulled Course pointer (0VDC) the computer should not try to turn when changing modes from HDG to NAV if all the signals are nulled.

Curious to know what type of compass system you have. Is it the KCS-55A (KI-525A) or do you have glass? How drastic is the oscillation? How long does it take to make one cycle? Do you happen to have a video of the oscillation? More information would be needed to try and isolate the issue.

@GMBrown We still support the KY197 units, if you would like a rough estimate and lead time give us a call and ask for Mike. 316-946-4870 Thanks