SERVICE DIRECTIVE BULLETIN NO. T-039 Revision 3 Page 1 of 10
DATE: July 6, 2011
1. SUBJECT: Cyclic Trim System – Cyclic Trim Assembly Kit for the Lateral and Longitudinal Trim Actuator Assemblies

2. MODEL: TH-28, 480, 480B
3. EFFECTIVITY: S/N 5138 and prior

4. REFERENCE: Enstrom TH-28/480 Se ries Maintenance Manua l, Latest Revision

5. BACKGROUND: Enstrom has received two reports of failure in the cyclic trim system in the field. A failed trim relay has reportedly caused the trim actuator to runaway and bottom out against the motor housing. Such an event will cause the circu it breaker to trip, leaving the trim fixed. If the trim runaway occurs in the aft or right directi on, the actuator will bottom out and no loss of control authority will occur, although the cycl ic control forces will be higher than normal. On further analysis of the condi tion, it was determined that if th e trim runaway occurs in the forward or left directions, the actuator will run until it fouls the limit switch bracket and the circuit breaker trips. In this case, there may be a significant loss of control authority in addition to the higher control forces whic h could result in an unsafe condition. This condition can only occur on aircraft equipped with P/N 4199059-3 Trim Switch Module Assembly containing a M83536/10-024M Tr im Relay (Figure 1). Aircraft equipped with P/N 4199059-1, 4192102-4 or 4192102-903 Trim Switch Module Assembly containing a solid state relay (Figure 2) are not at risk because those switches do not have a failure mode that could cause a runaway. Enstrom has developed a replacement limit switch bracket to provide a positive stop for the trim actuator. In the event of a trim actuator runaway, the new bracket will stop the actuator, causing the circuit breaker to tr ip, before any significant loss of control authority occurs. The cyclic forces may be high, but the aircraft will be controllable. This Service Directive Bulletin (SDB) is intend ed to make operators aware that the cyclic trim assembly modification kit, P/N 4230045-1, c ontaining the upgraded bracket is available and to provide instructions to perform the modification.SERVICE DIRECTIVE BULLETIN NO. T-039 Revision 3 July 6, 2011 Page 2 of 10

6. COMPLIANCE: Before further flight, insert the attached pa ge into the Emergency Section of the Flight Manual. Compliance with this SDB must be completed within the next 5 hours or at the next annual or 100 hour inspection, whichever occurs first, for aircraft equipped with P/N M83536/10- 024M trim relays. Until the new bracket is installed, operators ar e cautioned to be aware of anomalies in the trim system that might indicate an impending issue with the relay. This may include trim not operating when the switch is engaged, the trim not stopping when the switch is released, or the circuit breaker trips. If these or ot her unusual conditions are noted, the operator should pull the trim circuit breaker. The flight may be completed with the trim circuit breaker pulled, but this SDB should be complied with before further flight. If the aircraft is ever converted from the solid state switches to relays, this bulletin must be accomplished at the same time. Modify the lateral and longitudinal trim act uator assemblies in accordance with the procedure provided in paragraph 6.1. Upon co mpletion, perform an operational check and flight test as specified in paragraphs 6.2 and 6.3.

NOTE
Perform all maintenance in accordance with the TH-28/480 Series Maintenance Manual.

6.1 MODIFICATION: A. Determine if the trim actuator assembly has shims between the switch plate and the housing (Figure 3 and Figure 6). If the a ssembly contains shims complete the following:
1. Using the cyclic control, fully extend the motor.
2. Measure the distance from the motor hous ing to the bottom of the spring capsule (Figure 6). Record this di stance (‘Max’) in Table 1.
3. Repeat for the second trim actuator assembly, if necessary.B. Set the lateral and longitudinal trim actuator assemblies to a neutral position (midtravel). C. Disconnect the battery.

NOTE Remove the battery, if required, to faci litate removal of the longitudinal trim actuator assembly.

D. Remove the lateral and longitudinal trim actuator assemblies from the aircraft in accordance with Paragraph 12-69 of the maintenance manual.
1. Remove the mounting hardware as shown on Sheet 3, Zones A-1 and B-1.SERVICE DIRECTIVE BULLETIN NO. T-039 Revision 3 July 6, 2011 Page 3 of 10

E. Disassemble the trim actuator assembly.
1. Remove P/N 28-16636-3 trim switch assembly from the actuator assembly by removing the safety wire and two AN 502-10-8 and AN960-10 washers. Retain the washers. The screws may be discarded.
2. Mark the wires at the connector loca tions of the P/N 28-16636 trim switch assembly so they can be reinstalled correctly.
3. Retain shims P/N 4166031-11, if installed. F. Disassemble the trim switch assembly.
1. Remove P/N 28-16624-3 shield from the trim switch assembly by removing four AN515-4R12 or AN515-4R10 screws, AN960-4L washers, AN935-4 lock washers, and AN340-4 nuts.
2. Retain all removed hardware except the AN515-4R10 screws.
3. Disconnect the two wires from the V3-1 micro-switches that pass through the shield.
4. Remove and discard P/N 28-16614-3 switc h bracket and P/N 28-16624-3 shield. G. Re-assemble the switch assembly.
1. Route wires through new P/N 28-16624-11 shield.
2. Slide new shrink tubing onto the wires, as required.
3. Reconnect wires to the switches per the locations marked in step E.2.
4. Position the shrink tubing ove r the connections, and shrink.
5. Assemble new P/N 28-16614-5 bracket, new P/N 28-16624-11 shield, and micro switches using hardware re tained in step F.1. NOTE: AN515-4R10 screws must be replaced by MS35206-219 screws provided in the kit. H. Disassemble the spring housing a ssembly from the actuator assembly.
1. Unscrew P/N 4166031-( ) 1 spring housing assembly (counter clockwise) from the actuator assembly.
2. Remove NK500-8-5 screw and AN960-8L washer from P/N 4166031-( ) spring housing assembly as shown on Sheet 3, Zone B-4.
3. Discard screw and washer.

1 Dash number of spring housing assemb ly varies based on configuration.SERVICE DIRECTIVE BULLETIN NO. T-039 Revision 3 July 6, 2011 Page 4 of 10 I. Disassemble the P/N 28-16613-1 actuator from the spring housing assembly.
1. Remove the safety wire and two AN503-8-6 screws as shown on Sheet 3, Zone B-4.
2. Retain the screws.
3. Discard the actuator.
J. Install new P/N 28-16613-3 actuato r onto the spring housing assembly.
1. Heat the actuator, if necessary, to facilitate installa tion over the housing.

NOTE It may be necessary to chamfer the I.D. of the actuator to get it to slide onto the housing.

NOTE Ensure that the trim actuator, P/N 28- 16613-3, is installed properly over the spring housing assembly.

2. Reinstall two AN503-8-6 screws and one kit-supplied AN503-8-6 screw.
3. Safety wire with MS20995C25 as shown on Sheet3, Zone B-4.

NOTE Cotter pins, Safety wire, and VC-3 Vibra-Tite Thread Locker are not supplied with the kit and must be fu rnished by the installer.

4. Lubricate the threaded shaf t with Aeroshell 22 grease. K. Screw the spring housing assembly back onto the threaded shaft. L. Re-assemble the trim actuator assembly.
1. Assemble the new switch assembly and the trim actuator assembly with the two kit-supplied AN502-10-10 sc rews and the retained washers from step E.1. NOTE: Re-assemble using the same shims, P/N 4166031-11, installed between the switch assembly and the motor housing, if used in the orig inal installation. Substitute the kit-supplied AN502-10-12 screws for AN502-10-10, if necessary.
2. Safety wire with MS20995C32 as shown on Sheet3, Zone B-4.

NOTE Cotter pins, Safety wire, and VC-3 Vibra-Tite Thread Locker are not supplied with the kit and must be fu rnished by the installer.

M. Apply power to the trim actuator assembly to check and adjust the travel of the spring housing.
1. Install the electrical connectors.SERVICE DIRECTIVE BULLETIN NO. T-039 Revision 3 July 6, 2011 Page 5 of 10 2. Install and reconnect the battery.
3. Both trim actuator assemblies can be elect rically tested from either the left or right hand side of the aircraft, whicheve r location is more convenient. Set the trim actuator assembly on a portable bench or suitable stable surface to perform the check and adjustments. N. Check the spring housing travel and adjust the switch positions to ensure that the retracted and extended spring housing travel are within the limits specified on the drawing or as determined in the note below. Enlist a second person to assist with the cyclic operation while conducting measur ements and adjustments (Figure 5).

CAUTION To prevent damage to the switch assemb ly, immediately stop applying trim to the cyclic if the actuator will run out beyond the length allowed by the bracket slot.

NOTE If no shims are installed, the retracted travel or minimum stro ke limit is 0.125” +0.05”/-0.00”. The extended travel or ma ximum stroke limi t is 1.95” +0.00”/- 0.05”. If shims are installed, the extended travel or maximum travel limit is the ‘Max’ dimension measured in Step A.2 +0.00”/-0.05”. The minimum travel limit ‘Min’ is the difference between this dimension and 1.825” +0.05”/-0.00” (Figure 6).

1. To adjust the spring housing travel, loosen the switch mounting hardware to set the switch position(s) as necessary to bring the spring housing travel within limits. For example, to shorten the sp ring housing extension, loosen the switch mounting hardware for the extending switch and adjust the switch position inward (Figure 3).
2. Check spring housing travel to verify that proper adjustment was made.

NOTE If is not possible to achiev e the limits after adjusting th e switch positions, either the bracket slot or the switch screw sl ots may be filed to achieve the travel limits. The maximum amount that the bracket slot may be filed is 0.040”.

3. When the switch adjustments are complete, apply VC-3 Vibra-Tite to the exposed screw threads and nut face.
4. Disconnect the battery.
5. Remove the battery if it was re-installed in Step M. O. Install the lateral and longitudinal trim actuator assemblies in the aircraft in accordance with Paragraph 12-74 of the maintenance manual. P. Install and reconnect the battery. Q. Check the clearance of the spring housing with the cyclic bellcranks:SERVICE DIRECTIVE BULLETIN NO. T-039 Revision 3 July 6, 2011 Page 6 of 10

1. Extend the actuator to full travel. (Trim full forward or full left).
2. Move the cyclic full Aft/Right.
3. Verify there is clearance between the end of the spring capsule and the bellcrank (Figure 4).
4. If the spring capsule contacts the bellcrank, rem ove the P/N 4166031-11 shims from between the switch assembly and th e actuator and re-ins tall and re-safety the switch assembly.
5. Repeat steps 1-4 as required.
6. If the bellcrank contacts the spring capsule and there are no shims, re-check the travel in accordance with step N.
7. If the travel is correct an d the spring capsule still c ontacts the bellcrank, contact Enstrom Customer Service.

6.2 OPERATIONAL CHECK: A. Conduct an operational check of the trim limits.
1. Verify the trim operates in the correct direction.
2. Cycle each time actuator full travel each direction to verify the limit switches work properly.
3. Trim the cyclic full forward and verify the travel is not restrict ed in any direction.
4. Repeat Step 2 for the other three directions.
5. Return the trim to neutral (center the cyclic).

6.3 FLIGHT TEST A. Perform a flight test to verify trim authority.
1. Verify the aircraft can be trimmed in a hover.
2. Verify the aircraft can be trimmed at V NE or V H , whichever is lower.

NOTE
V H is the speed in level flight at maximu m continuous power. Do not exceed any engine, transmission or V NE limits.

CAUTION
V NE and V H vary depending on aircraft gross we ight, center of gravity, pressure altitude, and temperature. Do not exceed V NE for the flight conditions. See the appropriate Rotorcraft Flight Manual.SERVICE DIRECTIVE BULLETIN NO. T-039 Revision 3 July 6, 2011 Page 7 of 10

6.4 PARTS:
A. Kit P/N 4230045-1 includes the following parts unless otherwise noted.

Part Number Description Quantity 4230045 Drawing Cyclic Trim Assembly Kit Drawing, Sheet 2 and Sheet 3 1

28-16614-5 Bracket 2 28-16624-11 Shield 2 28-16613-3 Actuator 2 AN502-10-10 Screw 4 AN502-10-12 Screw 2 AN503-8-6 Screw 2 MS35206-219 Screw 8 FIT-221V-1/4 Shrink Tubing 2 inches

NOTE The following parts are not supplied with the kit and must be furnished by the installer.

Aeroshell 22 Grease A/R MS20995C25 Safety Wire (See Note below) A/R MS20995C32 Safety Wire (See Note below) A/R MS24665-151 Cotter Pin 2 MS24665-153 Cotter Pin 2 VC-3 Vibra-Tite Thread Locker A/R

7. SPECIAL TOOLS: Heat gun and precision ru ler, or equivalent measuring device
8. MAN-HOURS: 4 hours (2 hours per trim actuator assembly)

9. WARRANTY: Per En strom Warranty Policy

10. WEIGHT CHANGE: None

11. LOG BOOK ENTRY:
Record this modification in detail as required for maintenance actions.
12. REPETITIVE ACTION: NoneSERVICE DIRECTIVE BULLETIN NO. T-039 Revision 3 July 6, 2011 Page 8 of 10

Figure 1: Lateral Cyclic Trim Switc h Module and Trim Actuator Assembly

Figure 2: Solid State Trim Switch Module (Lateral Trim Actuator) LATERAL TRIM ACTUATOR ASSEMBLY Actuator Retracted TRIM SWITCH MODULE P/N 4199059-3 Assembly P/N M83536/10-024M Relays

Cyclic Bellcrank (Ref)

TRIM SWITCH MODULE P/N 4199059-1 Assembly P/N 4192102-4 Assembly P/N 4192102-903 AssemblySERVICE DIRECTIVE BULLETIN NO. T-039 Revision 3 July 6, 2011 Page 9 of 10

Figure 3: Trim Actuator Assembly (Lateral Trim Actuator Retracted)

Figure 4: Spring Housing a nd Cyclic Bellcrank Clearance Clearance

Cyclic Bellcrank Spring Housing Fully Extended Spring Housing (Retracted) Micro Switch (Extend) Installation Screws Micro Switch (Retract) Installation Screws Motor Housing (Ref)

Location of P/N 4166031-11 Shim
, If InstalledSERVICE DIRECTIVE BULLETIN NO. T-039 Revision 3 July 6, 2011 Page 10 of 10

Figure 5: Maximum Travel Limit at 1.95”

Figure 6: Actuator Travel Limits with a Shim

Table 1. Actuator Travel Limits for Trim Actuator Assemblies with a Shim

S/N Extended Travel Limit ‘Max’(+ 0.00”/-0.05”) (inch) Retracted Travel Limit ‘Min’ (+ 0.05”/-0.00”) (inch) (Note 1)

Note 1: Subtract 1.825 from ‘Max’ to calculate the ‘Min ’ travel limit.