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Autopilot Interface, Setup and Flight Calibration

Part I: Autopilot Interface
Before doing an installation; it is a must to fly the aircraft and perform an Autopilot/Flight Director checkout. By this I mean that you should first fly the Heading Mode and Altitude Hold mode to ensure that the Autopilot/Flight Director is working correctly. Check for good Roll Rate when manually turning the heading Bug from Right to Left. Also check that it does center back up under the Lubber line on the existing HSI. Next, you will need to perform an ILS approach. Make sure that the intercept angle is 30-45 degrees and that the capture of the Localizer the aircraft is not “S” turning down the ILS. Once the Glide Slope has captured then monitor the Lateral and Vertical track all the way down to minimums.
This will give you a good idea on how responsive the Autopilot is before the installation of the EHSI (SN3500, SN4500). Also this is a good time to check out the rest of the Avionics that you will be interfacing to us for proper operation.

Once this has been accomplished you are ready to interface the autopilot system. A few things to consider about the interface to the Autopilot.
On the existing HSI you will need to identify the Heading & Course Datum wiring and excitation if you are interfacing via AC signals. If you find that the 26vac for the Heading & Course Datum is coming from the Flight Director computer, then you will want to connect it to the EHSI P2-10 and the FCS Emulation Page 9 Excitation will be set to External for SN4500 or DC for SN3500. This is so that we can sync to the correct phase for proper operation. For a system that is using the same voltage excitation as the Directional Gyro input then we will sync off of P1-22 or ( P1-16 for SN3500) and the excitation on Page 9 FCS Emulation will be set to AC. For a DC system for Heading & Course Datum does not require AC excitation. Next we need to take into consideration if this Autopilot/Flight Director system will be utilizing “Roll Steering” whether it is from an FMS or GPS System utilizing a Garmin GAD 42, DAC GDC31 or Stec ST901.

Example 1.
Dual Garmin 400/500 GPS systems to any Roll Steering Platform.
Normally you would interface the GPS 429 to the Roll Steering Module for a single Garmin, However when you have both Garmins interfaced to us; you will need to add a relay so that you can switch the GPS 429 from either Garmin to the Roll Steering module or input to a Autopilot Computer such as a Stec 55x via controlled by our P3-8 discrete relay drive out.

Example 2.
Dual Nav receivers and FMS (UNS-1X & GNS-XLS).
In most installations you will find that the existing wiring for the interface of the FMS roll steering will not have to be touched. Verify that when you are in an ILS Approach Mode that the Roll Steering Valid Flag and Steering is disabled. In some installations we have had to add a relay that is controlled by the FCS ILS Energize from out P2-27 (FCS ILS/APPR) low logic. When an ILS is tuned in, but the EHSI is displaying GPS and the autopilot is in NAV Mode the autopilot will be flying the roll steering from the FMS computer. When the pilot select’s either ILS 1 or ILS 2 on the EHSI a “low” will leave P2-27 of the EHSI and energize the relay breaking the Roll Steering Flag and input if needed while supplying a ground to the Flight Director Computer for ILS mode. At this time selection of Approach Mode will process the analog signals from the SA4500 P2 (FCS output) connector to the Autopilot/FD system.

Determine what wiring is going to be used from the SA4500/3500 P2 connector to the Autopilot System. In some cases you would be installing new wiring. Most cases you will utilize the existing wiring. Most complex installations will use a relay to display the analog information on the HSI and to the autopilot via a switch on the pilot’s instrument panel. Normally you would find the relay and take away the connections for the Nav Receiver and the analog FMS outputs. These would be stowed. Now the wiring at the HSI is going straight to the Autopilot/Flight Director System. You always want to make sure that you have removed all Flags and deviation signals from the NAV Radio’s when interfaced via our P2 connector. Existing loads like a VIR30 Nav Super Flag still connected to the system can give you a FCS feedback error. Any additional loading on the FCS interface can cause this error.

Part II: Autopilot Setup & Calibration

Next determine the Heading and Course Datum Scaling per degree.
Once this has been done then we can select the correct selection on the FCS Emulation Menu Page 9. You will need a Generator capable of generating Localizer and Glide Slope signal.

Example 1:
You have a STEC 55x that is set from the factory for the King KI-525 emulation, then you would select the King KI-525 from the menu on Page 9 of the SA4500/3500. This will preset the lateral scaling and direction control.
Once this has been done then we will need to do a ground check for the autopilot. With the autopilot engaged in Heading mode turn the Heading bug to the Right, the Yoke should go right if it is reversed then go back into maintenance mode on Page 9 FCS Emulation and change the Heading +Right to +Left, then recheck the Heading mode. Also it should zero out the drive under the lubber line.
With the generator supplying a full LEFT and a full UP we are ready to check the ILS function of the Autopilot. Engage the NAV Approach mode with the Course Pointer under the lubber line. As the left-right comes in about 50% then you should go into track mode. Center the Left-Right and make sure the course pointer is under the lubber line. Next, you will vary the left/right deviation making sure the yoke is following correctly (with a left signal the yoke should go left). Next, center the needle and move the Course Needle to the right. The autopilot should go Right if it is reversed then you will need to back into maintenance mode and on Page 9 change the CRS DAT from +Right to +Left.
Once this is done then pull the yoke back half way and engage the Altitude Hold mode on the autopilot. Bring down the Glide Slope signal until it captures and drops the Altitude mode. Vary the Glide Slope signal up and the yoke should go up, then down and the yoke should go down, Once this pass’s then we are ready for a flight Calibration.

Flight Calibration.
Now that the ground checks have passed we need to do a Test Flight. Once on the air we will want to check the performance of the Heading Mode. Once heading and Altitude have been selected on the autopilot then rotate the heading bug at lease 45 degree’s from the lubber line. Allow the system to come out of the roll and the heading bug should be under the lubber line. If you are tracking off of the heading bug verses the Lubber line, then you will need to adjust the REF V in the Heading DAT section Page 9 in the 3500/4500. Also check the roll rate and if it is to responsive then you will need to decrease the SVL V/D mili volts per degree. If the aircraft has a slow roll rate then you will increase the setting as needed. Next we want to check the ILS for proper operation.
Intercept the ILS at 30-40 degree’s; with the Autopilot in the Heading and Approach mode of operation, once the Left-right Signal has been captured the aircraft should turn on course for the ILS. The aircraft should turn on course with very little overshoot. If you are “S” turning down the ILS you SVL V/D for the Course Datum section on Page 9 in the maintenance menu will have to be adjusted. Normally when you have a high rate of “S” turning you will need to decrease the voltage per degree. If you are sluggish then you will need to increase this voltage. Once this has been satisfied pay attention on how the system is tracking the ILS. If you are right or left of the inbound course you will need to adjust the Lateral Offset on Page 10 of the maintenance menu. You can adjust this in flight while in maintenance mode and monitoring the track down the ILS. Increasing the voltage should move the aircraft to the right and decreasing the offset will move the aircraft to the left. Note this adjustment only works when the autopilot is interfaced to our FCS output connector P2. If you are tracking off on the ILS and you are using the existing wiring to the autopilot then you can adjust the REF V in the CRS DAT section on page 9 of the maintenance menu to center up on the ILS. Once the ILS has been satisfied then check the VOR and GPS track modes, Of course if you have any problems Please give us a call at Product Support.