SERVICE DIRECTIVE BULLETIN NO. 0110 Revision 4 Page 1 of 9 DATE: January 23, 2012
1. SUBJECT: Cyclic Trim System – Cyclic Trim Assembly Kit for the Lateral and Longitudinal Trim Actuator Assemblies
2. MODEL: All F-28F, 280F, and 280FX models equipped with 24 volt D.C. system; Any F-28F model equipped with a 12 volt D.C. system with trim relays (S/N 815 only); Any F-28C, F-28C-2, or 280C models th at have been converted to a 24 volt D.C. system+
3. EFFECTIVITY: F-28F Series: Serial Numbers 828 and prior 280FX Series: Serial Numbers 2133 and prior

4. REFERENCE: Enstrom F-28A/F-28C Series Maintenance Manual , Latest Revision Enstrom 280/280C Series Mainte nance Manual, Latest Revision Enstrom F-28F/280FX Series Mainte nance Manual, 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 KUP14D55-24, KUP14D55- 472, M83536/10-015M, or M83536/10-024M trim relays (Figure 1). Aircraft equipped with solid state trim switch units P/N 4199059-1 or 4 192102-( ) (Figure 2) are not at risk because those units do not have a failure mode that co uld cause a runaway. Aircraft equipped with a reversible trim motor, P/N 28-16621 (For d Motor Co. C1AZ-14553A) or P/N AD1R-10 (Signal Electric), are not at risk because the tr im system does not use relays or solid state trim switch units. NOTE: If the electric motor on the trim actuator has three wires, it is not affected. All motors in systems with relays or solid state trim switc h units have only two wires.SERVICE DIRECTIV E BULLETIN NO. 0110 Revision 4 January 23, 2012 Page 2 of 9

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 28-01063, c ontaining the upgraded bracket is available and to provide instructions to perform the modification.

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, whicheve r occurs first, for aircra ft equipped with P/N KUP14D55- 24, KUP14D55-472, M83536/10-015M, or M83536/10-024 M trim relays. See Figure 1 for a pictorial example of a relay. Note: This includes aircraft modified per SIL 0164. If the aircraft is ever converted from the solid state trim switch units to relays, this bulletin must be accomplished at the same time. Compliance with this SDB is not required for airc raft equipped with a reversible trim motor, P/N 28-16621 (Ford Motor Co. C1AZ-14553A) or P/N AD1R-10 (Signal Electric). 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 circuit breaker pulled, but this SDB should be complied with before further flight. 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 wi th the F-28F/280F Series Maintenance Manual or in accordance with the F-28C/ 280C Maintenance Manual, as appropriate.

6.1 MODIFICATION:

A. Set the lateral and longitudinal trim actuator assemblies to a neutral position (midtravel).

B. Remove the seat deck and the copilot side floor panel for access to the trim actuator assemblies.SERVICE DIRECTIV E BULLETIN NO. 0110 Revision 4 January 23, 2012 Page 3 of 9
C. Remove the lateral and longitudinal trim actuator assemblies from the aircraft in accordance with the applicable maintena nce manual (F-28F/280F: Paragraph 12-7.B and 12-7.C; F-28A/F-28C/280/280C: Section 11, page MM-11-9).
1. Lateral trim actuator only: Remove the sp ring assembly to facilitate removal of the trim actuator assembly as show n on Sheet 2, Zone A-4. Mark the hole locations on the spring bracket used for the springs before disassembly.
2. Remove the mounting hardware as shown on Sheet 2.

NOTE When removing the actuator assemblies, note the orie ntation of hardware and location of spacers, etc. Retain the hardware and re-install in the original configuration.

D. 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 tw o AN502-10-8 and AN960-10 washers.
2. Retain the washers.
3. Discard the screws.
4. Mark the wires at the connector loca tions of the P/N 28-16636 trim switch assembly so they can be reinstalled correctly.

E. Disassemble the trim switch assembly.
1. Remove P/N 28-16624-3 shield from the trim switch assembly by removing four AN515-4R12 screws or AN515-4R10 sc rews, AN960-4L washers, AN935-4 lock washers, and AN340-4 nuts as shown on Sheet 1, Zone A-3.
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.

F. 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 D.4.
4. Position the shrink tubing over 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 E.1. NOTE: AN515-4R10 screws must be replaced by MS35206-219 screws provided in the kit.SERVICE DIRECTIV E BULLETIN NO. 0110 Revision 4 January 23, 2012 Page 4 of 9
G. Unscrew P/N 28-16618 spring housing assemb ly (counter clockwise) from the trim motor assembly.

H. Disassemble the P/N 28-16613-1 actuat or and P/N 28-162043-1 bracket from the spring housing assembly. (P/N 28-162043-1 bracket is used for the lateral trim actuator only.)

NOTE On aircraft manufactured prior to 1993, the actuator was installed to the spring housing assembly with NK5008 screws. The NK5008 screws do not have provisions for safety wire. Replace the NK5008 screws with kit-supplied AN503- 8-6 or AN503-8-8 screws, as applicable.

1. Lateral Assembly: Remove safety wi re, AN503-8-6 screw, AN503-8-8 screws, and AN960-8L washers from the spring hous ing assembly as shown on Sheet 1, Zone B-3. a. Retain the washers and AN503-8-8 screws. b. Discard the AN503-8-6 screw, actuator, and bracket.
2. Longitudinal Assembly: Remove NK 5008-5 screw, AN503-8-6 screws, and AN960-8L washers from the spring housi ng assembly as shown on Sheet 1, Zone B-3. a. Retain the washers and AN503-8-6 screws. b. Discard the NK5008-5 screw and actuator.

I. Install new P/N 28-16613-3 actuato r onto the spring housing assembly.
1. Heat the actuator, if necessary, to f acilitate installati on 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. Lateral Assembly: Install new P/N 28- 162043-3 bracket (lateral trim actuator only). a. Reinstall two AN503-8-8 screws a nd one kit-supplied AN503-8-8 screw and AN960-8L washers. Use retained hardware from step H.1.a.
3. Longitudinal Assembly: Reinstall two AN503-8-6 screws and one kit-supplied AN503-8-6 screw and AN960-8L washers. Use retained hardware from step H.2.a.SERVICE DIRECTIV E BULLETIN NO. 0110 Revision 4 January 23, 2012 Page 5 of 9

4. Safety wire with MS20995C25 as shown on Sheet 1, 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.

5. Lubricate the threaded shaf t with Aeroshell 22 grease.

J. Screw the spring housing assembly back onto the threaded shaft.
K. Re-assemble the trim actuator assembly.
1. Install the new switch assembly onto the tr im actuator assembly with the two kitsupplied AN502-10-10 screws and the retained washers from step D.1.
2. Safety wire with MS20995C32 as shown on Sheet1, Zone B-1.

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.

L. Apply power to the trim actuator assembly to check and adjust the travel of the spring housing.
1. Install the electrical connectors.
2. 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.

M. 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 3).

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 The retracted travel or minimum st roke limit is 0.125” +0.075”/-0.00”. The extended travel or maximum st roke limit is 1.95” +0.00”/-0.05”.SERVICE DIRECTIV E BULLETIN NO. 0110 Revision 4 January 23, 2012 Page 6 of 9

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 4).
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. Verify there is no interference be tween the P/N 28-162043-3 bracket and the switch assembly hardware.

N. Install the lateral and longitudinal trim actuator assemblies in reverse procedure as removed.
1. Lateral trim actuator assembly only: Inst all the spring assembly. Install the spring ends in the holes marked on the bracket in Step C.1.

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 tr avel is not restricted 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.SERVICE DIRECTIV E BULLETIN NO. 0110 Revision 4 January 23, 2012 Page 7 of 9

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.

6.4 PARTS:

A. Kit P/N 28-01063-1 includes the foll owing parts unless otherwise noted.

Part Number Description Quantity 28-01063 Drawing Sheet 1 and Sheet 2 1 28-162043-3 Bracket (Lateral trim actuator assembly only) 1 28-16613-3 Actuator 2 28-16614-5 Bracket 2 28-16624-11 Shield 2 AN502-10-10 Screw 4 AN503-8-6 Screw 3 AN503-8-8 Screw 3 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 furnishe d by the installer.

Aeroshell 22 Grease A/R MS20995C25 Safety Wire (See Note below) A/R MS20995C32 Safety Wire (See Note below) A/R VC-3 Vibra-Tite Thread Locker A/R

7. SPECIAL TOOLS: Heat gun and precision ru ler, or equivalent measuring device
8. MAN-HOURS: 8 hours (4 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 DIRECTIV E BULLETIN NO. 0110 Revision 4 January 23, 2012 Page 8 of 9

Figure 1: Trim Relay (M83536/10-024M Relay Shown)

Figure 2: Solid State Trim Switch Unit (NOTE: Color, size, location of the solid state trim switch unit may vary.)SERVICE DIRECTIV E BULLETIN NO. 0110 Revision 4 January 23, 2012 Page 9 of 9

Figure 3: Maximum Stroke Limit at 1.95”

Figure 4: Trim Actuator Assembly (Lateral Trim Actuator Retracted) Micro Switch (Extend) Installation Screws

Micro Switch (Retract) Installation ScrewsSPECIAL ADDENDUM TO FL IGHT MANUAL EMERGENCY PROCEDURES PER: SERVICE BULLETIN DIRECTIVE 0110 REV 4

January 23, 2012 Page 1 of 2 Trim Failure/Trim Runaway
Operators must observe the following:
They should locate the TRIM circuit breaker or circuit breaker switch so they can find it quickly in an emergency.
Until the new bracket is available and installed, operators are cautioned to be aware of anomalies in the trim system that might indi cate an impending issue with the relay. This may include trim not operating when the switc h is engaged or the trim not stopping when the switch is released. If th ese or other unusual conditions are noted, the operator should:

A. Immediately stop using the trim and pull the TRIM circuit breaker or select the trim switch to OFF to deactivate the circuit. Leave the circuit breaker out for the remainder of the flight.

B. If the pilot determines the flight can be continued safe ly, without use of the trim, flight may be continued to the next destination.

C. If the pilot has any safety concerns, a landi ng should be made as soon as practical.

a. If there is a significant reduc tion in the longitudinal contro l, the pilot should plan a landing where a shallow approach and a run on landing can be made.

i. Avoid any maneuvers, such as rapid decelerations, which may require forward cyclic for recovery.

ii. Perform a run-on landing as there ma y not be enough forward cyclic to level the aircraft and stop rearward mo tion if it is allowed to start drifting rearward from a hover.

b. If there is a significant reduction in the la teral cyclic control, it may be difficult or impossible to make turns to the left.

i. The pilot should plan a landing to an area where there is ample room to maneuver. The aircraft will fly in a ri ght crab, and maintaining a straight course may be difficult.

ii. Lateral course corrections can be made using pedal and longitudinal cyclic, but the aircraft may not be aligned with the ground course.

iii. Perform an approach to a low hover; forward speed can be stopped, but there may be some sideward drift.SPECIAL ADDENDUM TO FL IGHT MANUAL EMERGENCY PROCEDURES PER: SERVICE BULLETIN DIRECTIVE 0110 REV 4

January 23, 2012 Page 2 of 2 iv. Once forward speed is reduced in a low hover, the pilot can roll off the throttle and align the aircraft with th e direction of motion using the pedals prior to touching down.

v. If the pilot is having difficulty maintaining the approach course, the pilot should consider making a 360° turn to the right to line up on the final approach.

vi. Directional control is easier to main tain at airspeeds above 60 knots, but the pilot must plan to reduce fo rward speed prior to touchdown.

D. Ground the aircraft at the end of the flight . The aircraft should be grounded until the relays are replaced.