Bendix King 18049-0002 Synchro Transmitter – Aviation Component Guide

This guide covers everything a
maintenance technician, avionics engineer, or operator needs to know about the
Bendix King 18049-0002 Synchro Transmitter: what it is, how it works, its full
technical specifications, compatible aircraft and systems, installation and
wiring requirements, maintenance and inspection intervals, common failure modes
and troubleshooting, and where to source serviceable or overhauled units.

Component Overview

The Bendix King 18049-0002 Synchro
Transmitter is classified as a torque transmitter (TX) in the standard synchro
nomenclature system. Its function is to convert the mechanical angular position
of a rotating shaft – typically driven by a fuel quantity float, a control
surface sensor, a compass flux valve, or a similar position-sensing element –
into a proportional three-wire electrical signal that can be transmitted to a
remote synchro receiver or indicator.

The 18049-0002 part number places
this unit within the Bendix King component family that was produced under the
Allied Signal brand and subsequently transitioned to Honeywell following the
1999 acquisition. The 18049 series encompasses several variants distinguished
by suffix number, each calibrated for specific angular ranges, torque ratings,
or connector configurations. The -0002 suffix identifies the specific variant
covered in this guide, with its particular excitation voltage, accuracy rating,
and connector type.

Within the aircraft instrument
system, the Bendix King 18049-0002 Synchro Transmitter typically operates as
part of a synchro loop that also includes a receiver (RX or CT), a synchro
indicator, and in some systems a synchro control transformer used for
servo-driven instruments. The transmitter is the upstream element in this
chain: it converts shaft position to signal, and the downstream receiver
converts signal back to pointer or servo position.

Technical Specifications

The following specifications apply
specifically to the Bendix King 18049-0002 Synchro Transmitter. Technicians
should verify all values against the current Component Maintenance Manual and
applicable equipment specification sheet, as documentation takes precedence
over any third-party reference.

How a Synchro Transmitter Works

Understanding the operating
principle of the Bendix King 18049-0002 Synchro Transmitter is essential for
correct installation, fault diagnosis, and interpretation of test results. The
synchro system is one of the oldest and most reliable methods of transmitting
angular position data over a distance in aircraft applications, and its
operating principle has remained fundamentally unchanged for decades.

Basic Synchro Principle

A synchro transmitter is an
electromechanical transformer whose magnetic coupling between rotor and stator
varies with the angular position of the rotor. The rotor is a single-winding
coil energised by an AC excitation voltage – in the case of the Bendix King
18049-0002 Synchro Transmitter, 26V AC at 400 Hz. As the rotor turns, it
induces voltages in three stator windings spaced 120 degrees apart. The
amplitude and phase relationship of these three induced voltages is uniquely
determined by the rotor’s angular position.

At the receiving end, a synchro
receiver (or control transformer) with an identical stator configuration
receives these three signals. The voltages produce a magnetic field in the
receiver’s stator whose orientation matches the transmitter’s rotor angle. This
field drives the receiver’s rotor to align with it, positioning the connected
indicator pointer or servo motor to display or act on the transmitted angle.

Torque Transmitter Classification

The Bendix King 18049-0002 Synchro
Transmitter is specifically classified as a torque transmitter (TX type). In a
torque synchro system, the receiver rotor is allowed to rotate freely under the
torque produced by the magnetic field mismatch between transmitter and
receiver. This makes torque synchro systems simple and self-synchronising, but
also means they can only drive low-torque loads such as lightweight instrument
pointers. For higher-torque applications requiring servo actuation, control
transformer (CT) and control differential transmitter (CDX) configurations are
used instead.

The practical implication for
maintenance is that a torque synchro indicator connected to the Bendix King
18049-0002 Synchro Transmitter should move to align with the transmitter shaft
position without requiring any external power to the receiver rotor. If the
indicator requires a servo amplifier or shows hunting behaviour, the system is
likely configured as a control synchro loop rather than a simple torque loop,
and the diagnostic approach differs accordingly.

400 Hz Excitation

Aircraft synchro systems use 400
Hz AC rather than the 60 Hz used in ground-based systems because 400 Hz allows
smaller, lighter transformers and inductive components for the same power
handling capability. The 26V AC 400 Hz excitation required by the Bendix King
18049-0002 Synchro Transmitter is supplied by the aircraft’s 400 Hz AC bus,
typically derived from a dedicated inverter or the aircraft’s AC generation
system. Incorrect excitation frequency – for example, connecting to a 60 Hz
ground power supply – will cause the synchro to function but with significantly
degraded accuracy and increased heating.

Aircraft Applications and Compatibility

The Bendix King 18049-0002 Synchro
Transmitter has been installed across a broad range of aircraft types in fuel
quantity, flap position, trim position, and compass system applications. The
following categories represent the primary installation contexts.

General Aviation Applications

In general aviation aircraft, the
Bendix King 18049-0002 Synchro Transmitter is most commonly found in fuel
quantity system installations where a float-driven transmitter sends tank
quantity data to a cockpit indicator, and in flap position indicating systems
where a transmitter coupled to the flap actuator linkage drives a cockpit flap
position gauge. Aircraft models from Cessna, Beechcraft, and Piper produced
during the 1970s through 1990s frequently used Bendix King synchro components
in these roles, and many of those airframes remain in active service.

Commuter and Regional Aircraft

Commuter and regional turboprop
aircraft of the same era used synchro transmitter systems extensively for fuel
quantity, control surface position, and engine parameter indication. The Bendix
King 18049-0002 Synchro Transmitter and its variant series appear in the
approved parts lists of several Twin Otter, Beechcraft 1900, and similar
turboprop types. In these installations the transmitters may be part of a more
complex synchro loop involving differential transmitters and control
transformers, requiring a thorough understanding of the full system schematic
before troubleshooting any single component.

Military and Government Aircraft

The Bendix King 18049-0002 Synchro
Transmitter was qualified to MIL-E-5400 environmental standards, which made it
suitable for military applications. Various military trainer, utility, and
patrol aircraft used Bendix King synchro components under government
procurement. Maintenance on military applications may be subject to additional
documentation requirements and airworthiness oversight beyond civilian FAA
regulations.

Verifying Compatibility

Before installing the Bendix King
18049-0002 Synchro Transmitter on any aircraft, verify compatibility by cross-referencing
the part number against the aircraft’s Illustrated Parts Catalog (IPC) and the
applicable equipment installation drawing. Part number interchangeability
between synchro variants is not guaranteed and must be established through
engineering documentation rather than assumed from physical similarity. Synchro
transmitters that appear mechanically interchangeable may have different
electrical characteristics that produce incorrect indications without
triggering an obvious fault.

Installation and Wiring

Installation of the Bendix King
18049-0002 Synchro Transmitter must follow the aircraft-specific maintenance
manual and the component installation drawing. The following information covers
general principles applicable to most installations and is not a substitute for
aircraft-specific documentation.

Mechanical Installation

The transmitter is mounted via its
flanged housing to a bracket or mounting plate that positions the rotor shaft
in direct mechanical coupling with the position-sensing element – a fuel float
arm, a flap position rod, a gear position cam, or similar mechanism. The
coupling must be rigid enough to prevent backlash and compliant enough to
accommodate slight misalignment without imposing side loads on the transmitter
shaft. Excessive side loading accelerates bearing wear and is the most common
cause of premature mechanical failure in synchro transmitters.

Torque the mounting hardware to
the values specified in the installation drawing. Over-torquing the mounting
flange screws can distort the transmitter housing and affect rotor
concentricity. Apply thread-locking compound only where specified; many synchro
transmitter installations call for safety wire rather than adhesive locking due
to vibration environment requirements.

Electrical Connections

The Bendix King 18049-0002 Synchro
Transmitter uses an MS-style circular connector. Pin assignments follow the
standard synchro convention with rotor connections at R1 and R2 and stator
outputs at S1, S2, and S3. The table below summarises the pin functions.

Stator wiring harness runs should
be kept away from high-current DC conductors and audio-frequency wiring where
possible, as induced interference in S-wire runs can produce erratic indicator
behaviour that is difficult to distinguish from a faulty transmitter. Where
routing near interference sources is unavoidable, use shielded cable with the
shield grounded at one end only to prevent ground loops.

Post-Installation Functional Test

After installation, perform a full
angular sweep of the transmitter shaft through its operating range while
observing the connected indicator. The indicator should track smoothly and
accurately through the full range without sticking, jumping, or reversing
direction. Compare the indicator reading against a known reference at several
points across the range. Record the as-found accuracy at each test point and
verify it falls within the tolerance specified in the aircraft maintenance
manual.

Maintenance and Inspection

The Bendix King 18049-0002 Synchro
Transmitter is a sealed electromechanical unit with no user-serviceable
internal components. Field maintenance is limited to inspection, cleaning,
connector care, and replacement. Internal overhaul and calibration must be
performed by an FAA-certificated repair station holding the appropriate ratings
for this component class.

Scheduled Inspection

During scheduled airframe
inspections, inspect the Bendix King 18049-0002 Synchro Transmitter
installation for the following:

• Security of mounting hardware – check for
  looseness, corrosion, and proper safety wiring or locking
• Condition of the mechanical coupling –
  inspect for wear, backlash, and proper alignment
• Connector condition – inspect for corrosion,
  bent or pushed-back pins, damaged backshell, and proper locking
• Wiring harness condition – inspect for
  chafing, cracking insulation, and secure clamping along the harness run
• Case condition – inspect for cracks, impact
  damage, and security of the bonding jumper if installed

No lubrication of external
components is required or recommended unless specifically called for in the
aircraft maintenance manual. The transmitter shaft bearing is
factory-lubricated for life in sealed variants.

Overhaul Intervals

Many aircraft type certificates do
not specify a mandatory overhaul interval for synchro transmitters, treating
them as on-condition components to be replaced when inspection or functional
test reveals degraded performance. Where an overhaul interval is specified –
either in the aircraft maintenance manual or in an applicable airworthiness
directive – it must be complied with regardless of apparent serviceability.
Verify the current interval requirement in the aircraft’s maintenance program
documentation.

Removal for Shop Inspection

If the transmitter exhibits
symptoms consistent with internal wear – sluggish response, erratic indication,
or reduced accuracy that cannot be attributed to external causes – remove the
unit and send it to an approved repair station for bench testing and overhaul
assessment. Do not attempt to open, adjust, or repair the unit in the field.
Marking the transmitter with the aircraft registration, installation position,
and squawk description before shipping assists the repair station in performing
targeted testing.

Troubleshooting Common Issues

When a synchro-driven instrument
malfunctions, isolating whether the fault lies in the Bendix King 18049-0002
Synchro Transmitter, the wiring harness, the receiver, or the indicator
requires a systematic approach. The troubleshooting table below covers the most
common symptom patterns and their most likely causes.

Isolation Procedure

The most effective way to isolate
a suspected faulty Bendix King 18049-0002 Synchro Transmitter from a wiring or
receiver fault is to substitute a known-good transmitter of the same part
number into the installation and verify whether the symptom follows the unit or
stays with the installation. If the symptom moves with the transmitter, the
transmitter is at fault. If it remains with the aircraft installation, the
fault is in the wiring, connector, receiver, or indicator. isolating whether the fault lies in the Bendix King 18049-0002 Synchro Transmitter, the wiring harness, the receiver, or the indicator requires a systematic approach. In modern digital workflows, similar diagnostic thinking is used when tracking or verifying visual data, where tools can help identify the source and history of images through pattern analysis and recognition.

Before substitution testing,
verify that excitation voltage at R1 and R2 measures 26V AC at 400 Hz with a
calibrated AC voltmeter. An excitation fault will cause every transmitter
installed in that position to fail identically, which can mislead a technician
into condemning a serviceable unit.

Sourcing and Airworthiness

The Bendix King 18049-0002 Synchro
Transmitter is no longer in production as a new unit. Sourcing is through the
certified used parts market, approved repair stations carrying overhauled
exchange units, or aviation parts brokers who hold FAA Form 8130-3 tagged
serviceable stock.

Acceptable Serviceability Documentation

Any Bendix King 18049-0002 Synchro
Transmitter installed on a certificated aircraft must be accompanied by
documentation establishing its airworthiness. Acceptable documentation includes
an FAA Form 8130-3 Airworthiness Approval Tag issued by an FAA-certificated
repair station, an EASA Form 1 for European-registered aircraft, or a Return to
Service tag issued by the aircraft manufacturer’s authorised service centre
where applicable. Parts sourced without proper documentation cannot be legally
installed on certificated aircraft regardless of apparent condition.

Overhauled vs. As-Removed Units

Overhauled units from a reputable
repair station offer the best assurance of serviceability. An overhauled Bendix
King 18049-0002 Synchro Transmitter will have been disassembled, inspected,
cleaned, repaired as necessary, reassembled, and calibration-tested against the
manufacturer’s CMM acceptance standards before being released with an 8130-3.
As-removed units with traceability documentation may be serviceable but carry
more uncertainty – inspect the 8130-3 carefully for any limitations,
discrepancy notes, or as-removed rather than serviceable designations.

Approved Suppliers

Purchase from FAA-certificated
Part 145 repair stations or established aviation parts distributors who can
provide full traceability documentation. When evaluating a supplier, confirm
that the 8130-3 tag was issued by the repair station itself (block 14 signed by
an authorised release certificate holder) rather than simply passed through
from another source. Be cautious of online marketplaces offering aviation parts
without clear documentation – counterfeit and unapproved parts are a documented
problem in the aviation parts supply chain and their installation is both
illegal and dangerous.

Conclusion

The Bendix King 18049-0002 Synchro
Transmitter is a mature, well-understood component that continues to perform
reliably in service when correctly installed, maintained, and sourced from
approved channels. Its operating principle is straightforward, its failure
modes are predictable, and the diagnostic process is systematic enough that
most faults can be isolated to either the unit itself or the surrounding
installation without extensive specialist equipment.

The areas where technicians most commonly
encounter problems are not with the transmitter’s internal operation but with
the surrounding context: incorrect excitation voltage, reversed rotor polarity,
degraded connectors, and parts sourced without proper airworthiness
documentation. Addressing those factors first – before condemning the
transmitter itself – saves time, reduces unnecessary parts cost, and avoids the
risk of installing a serviceable unit into a faulty installation that will
damage it again.

For operators managing ageing
airframes that rely on Bendix King synchro instrumentation, the practical
priority is building a reliable supply chain for overhauled exchange units with
proper 8130-3 documentation. New production is not available, and as the pool
of serviceable cores diminishes over time, lead times for overhauled units from
approved repair stations are likely to extend. Establishing a relationship with
a reputable Part 145 repair station that specialises in legacy avionics
components is the most effective way to ensure continued availability of
airworthy Bendix King 18049-0002 Synchro Transmitter units for the service life
of the airframe.

Frequently Asked Questions

What does the Bendix King 18049-0002 Synchro Transmitter do?

The Bendix King 18049-0002 Synchro
Transmitter converts the mechanical angular position of a rotating shaft into a
proportional three-wire electrical signal that drives a remote synchro
indicator or receiver. It is used in aircraft fuel quantity systems, flap and
trim position indicating systems, and compass system installations where a
mechanical position must be accurately transmitted to a cockpit display located
some distance away from the sensing element.

Is the 18049-0002 still available new?

The Bendix King 18049-0002 Synchro
Transmitter is no longer manufactured as a new production unit. It is available
through the certified used parts market as overhauled exchange units with FAA
Form 8130-3 tags from approved repair stations, and occasionally as as-removed
units with traceability documentation. Always verify airworthiness
documentation before purchase and installation.

Can the 18049-0002 be substituted with a different part number?

Part number substitution for the
Bendix King 18049-0002 Synchro Transmitter requires engineering approval and
must be supported by an approved data source, such as an Approved Model List,
Supplemental Type Certificate, or aircraft manufacturer’s engineering order. Physical
interchangeability does not establish electrical compatibility. Different
variants in the 18049 series may have different electrical accuracy ratings,
excitation characteristics, or connector configurations that produce incorrect
indications if substituted without engineering verification.

What excitation voltage does the 18049-0002 require?

The Bendix King 18049-0002 Synchro
Transmitter requires 26V AC at 400 Hz applied to the R1 and R2 rotor
connections. This is supplied by the aircraft’s 400 Hz AC power bus. Applying
the wrong voltage or frequency – including 115V AC or 60 Hz ground power – will
damage the unit and produce incorrect indications. Always verify excitation
voltage at the connector with a calibrated True RMS AC voltmeter before condemning
or replacing the transmitter.

How do I know if the transmitter is faulty or if the problem is in the
wiring?

The most reliable isolation method
is substitution with a known-good Bendix King 18049-0002 Synchro Transmitter of
the same part number. If the symptom follows the unit to another aircraft or
position, the transmitter is at fault. If the symptom remains in the original
installation position with the new unit, the fault is in the wiring, connector,
receiver, or indicator. Before substitution, always verify that 26V AC 400 Hz
excitation is present at the connector, as an excitation fault will cause all
transmitters installed in that position to fail identically.

Who can perform an overhaul on the 18049-0002?

Overhaul of the Bendix King
18049-0002 Synchro Transmitter must be performed by an FAA-certificated Part
145 repair station holding appropriate ratings for avionics and instrument
components. The repair station must perform an overhaul in accordance with the
Bendix King/Honeywell Component Maintenance Manual for this part number. Field
disassembly and repair by aircraft maintenance technicians is not authorised
and will invalidate the component’s airworthiness status.