1. EFD1000 to Century II/III Autopilot Interface
Training & Troubleshooting
Presented by
Tim McNany
Field Service Engineer
October, 2011

2. Agenda Century II/III Basics Radio Coupler types What’s a Lubber line
Roll Centering
Alignment to the ACU
Alignment of R1
Roll Centering Adjustment
Troubleshooting
HDG/CRS Datum signal flow
Slide 12

3. Operation of DG version Radio Couplers
Century II/III Basics
Operation of DG version Radio Couplers
1C388, 1C388M, 1C388C, 1C388MC
Uses Left/Right deviation from the GPS/NAV or in the case of the EFD1000, the ACU.
ACU HDG Datum output (PFD HDG Bug) controls A/P HDG Mode
ACU HDG Datum output controls GPSS operation via autopilot HDG
Mode
ACU HDG Datum output controls the autopilot “CRS*” input in
NAV/OMNI/LOC Modes
*CRS input is the heading datum input with these radio couplers (the PFD HDG Bug will be used in place of the CRS pointer)

4. Operation of HSI version Radio Couplers
Century II/III Basics
Operation of HSI version Radio Couplers
1C388-2 and 1C388-3
Uses Left/Right deviation from GPS/NAV or in the case of the EFD1000, the ACU.
ACU HDG Datum output (PFD HDG Bug) controls autopilot HDG
Mode
ACU HDG Datum output controls GPSS operation via autopilot HDG
ACU CRS Datum (PFD CRS pointer) output controls the autopilot CRS input in NAV/OMNI/LOC Modes

5. Autopilot Basics Lubber line
12 o’clock position of the CRS Pointer or HDG Bug

6. Autopilot Basics
45⁰ right of Lubber line

7. Autopilot Basics
90⁰ left of Lubber line

8. Autopilot Basics Roll “null” Centering Symptoms
All autopilots have a roll centering adjustment including the Century II/III. The roll centering adjustment is used to “null” out any offsets in the VG (Attitude Indicator) or HDG Datum signal.
Most installations will require the adjustment of the roll centering pot after the installation of the EFD1000.
Why? The mechanical DG or HSI that is removed did not have a centered HDG Datum when the HDG Bug was under the lubber line. The ACU does.
Symptoms
HDG Bug does not center
in HDG Mode
Aircraft flies right or left of the runway during approach or the CDI does not center in NAV/LOC modes
Aircraft flies right or left of GPS course line in GPSS mode

9. When it’s not a Roll “null” Centering Issue
Autopilot Basics
When it’s not a Roll “null” Centering Issue
Usually the HDG bug is within 0-10 degrees of the lubber line if it is a roll null issue. If the HDG bug is out of center more than this it is more likely a wiring issue or an ACU with a shorted HDG or CRS output.
VG must be level (can be unplugged) during this test
Symptom
HDG Bug is more than 10° out of center when the yoke nulls in HDG Mode.
Causes
R1 has not yet been adjusted for a 45° intercept angle (see Slides 12-17)
Verify wiring between the ACU and the transformers is correct.
Check radio coupler pin A for 0vrms when the HDG Bug is under the lubberline. If not 0vrms then the ACU HDG Datum (pin 22) output has gone bad. Make sure the wiring is not shorted and then replace the ACU.

10. In Air - Roll “null” Centering Adjustments
Autopilot Basics
In Air - Roll “null” Centering Adjustments
(Follow autopilot manufacturers’ instructions)
Aircraft must be in proper trim (rudder and aileron)
Verify slip/skid ball is centered – if not, apply appropriate rudder command to center. If HDG bug is now centered no further action is required. (may look into adjusting rudder trim tab)
Make small adjustments to autopilot roll “null” centering pot
Allow 15 seconds or so for autopilot to settle
Re-adjust pot as necessary, waiting 15s between adjustments, until HDG Bug is centered or aircraft is on course

11. Century II/III Radio Coupler R1 Alignment and Theory
It is recommended that a pre-EFD1000 flight test be performed on the autopilot to verify acceptable operation
Disclaimer – The following pages contain information that should only be used to align the ACU to the radio coupler and it assumes the radio coupler was properly aligned and functioning correctly prior to the EFD1000 installation. Follow all autopilot manufacturers instructions for any needed autopilot alignments or for autopilot return to service instructions.
Radio Coupler
Computer AMP

12. Three ways to align the ACU to the Radio Coupler
Century II/III - Alignment
Three ways to align the ACU to the Radio Coupler
Prior to removal of the DG/HSI you would measure the HDG Datum voltage (radio coupler pin A) when the HDG Bug is 90⁰ off of the lubber line. After the EFD1000 installation, set R1 so that the ACU generates the same voltage at pin A.
Roll the vertical gyro (AI or Attitude Indicator) 10⁰ left and then put the HDG Bug 10⁰ left. Put the selector in HDG mode and engage the A/P. Adjust R1 so that the yoke is still. This may be the easiest option with the Century gyro substitution box.
Adjust R1 to produce a 45⁰ intercept angle in “OMNI” mode. Instructions to follow.

13. Century II/III - Alignment
Century II/III interface with Radio Couplers
1C388, 1C388M, 1C388MC, 1C388-C only
HDG Datum input only, therefore HDG Bug
controls HDG/NAV/OMNI/LOC Modes
CRS Pointer position is irrelevant
R1 is set for a 45⁰ intercept angle:
Procedure:
AI must be level (can be unplugged) during this test
1. Generate a full deflection CDI left using VOR/ILS signal generator
2. Position the HDG Bug 45⁰ right on the PFD
3. Engage the autopilot in “OMNI” mode
4. Adjust R1 until the yoke stops turning.

14. Century II/III - Alignment
Century II/III interface with Radio Couplers
1C388, 1C388M, 1C388MC, 1C388-C only
Likewise:
CDI full scale right
HDG Bug 45⁰ left
Nulls the yoke
If you have trouble adjusting R1 to stop the yoke movement . Turn the HDG bug from 5° to 90° to locate the spot where the yoke moves back and forth following the bug. If this position is less than 45° then R1 is too small. If it is higher than 45° then R1 is too large.

15. Datum Signal Flow
R1: KΩ

16. Century II/III - Alignment
Century II/III interface with Radio Couplers
1C388-2 and 1C388-3 only
These use CRS Datum input for
NAV/OMNI/LOC Modes
(HDG Bug position is irrelevant)
R1 is set for 45⁰ intercept angle:
Procedure:
AI must be level (can be unplugged) during this test
1. Generate a full deflection CDI left using a VOR/ILS signal generator
2. Position the CRS Pointer 45⁰ to right on the PFD
3. Engage the autopilot in “OMNI” mode
4. Adjust R1 until the yoke stops turning

17. Century II/III - Alignment
Century II/III interface with Radio Couplers
1C388-2 and 1C388-3 only
Likewise:
CDI full scale right
CRS Pointer 45⁰ left
Nulls the yoke
If you have trouble adjusting R1 to stop the yoke movement . Turn the CRS Pointer from 5° to 90° to locate the spot where the yoke moves back and forth following the CRS. If this position is less than 45° then R1 is too small. If it is higher than 45° then R1 is too large.

18. Datum Signal Flow
1C and -3: 0-5KΩ

19. On Ground - Roll “null” Centering Adjustments
Century II/III - Alignment
On Ground - Roll “null” Centering Adjustments
(Note – this will get it close. Follow autopilot manufacturers’ instructions for final adjustment)
Un-plug the VG (AI), (52C77, 52D267, etc)
Sync the HDG Bug to the lubber line
Engage the A/P in HDG mode
Adjust the autopilot roll centering pot until yoke is still
Do Not forget to re-connect the VG (AI) connector if removed!

20. Century II/III - Extras
The 1C388, 1C388C, 1C388M and the 1C388MC radio couplers can be replaced with a 1C388-2 or 1C388-3 radio coupler if the customer desires the CRS Pointer to drive the autopilot like an HSI.
If you are having difficulty obtaining the 45° intercept angles or the autopilot does not respond to the heading bug the way it did with the old DG installed then you could have one of the radio couplers with a lower input impedance. Try using a TY-145 or SP-67 transformer for T2 as shown in Installation Manual Rev Z or later.
The End