What are Electrolytic Leveling Switches and Why Should You Care?

June 2013

 

Per the L-3 Communications Vertical Gyro (VG206D) Component Maintenance Manual the table below lists the components that must be replaced with the new OEM components to comprise a complete overhaul of the displacement gyroscope.

L-3 Overhaul Components

L-3 Part Number

Description

Quantity

Locations

571-9445-01

Bearing, Ball, Annual, Fanged, Double Row

1

Inner Axis

571-9412-01

Bearing, Ball, Radial Retainer Flanged

1

Inner Axis

571-9439-01

Bearing, Ball, Annual

1

Inner Axis (Mod 22)

571-9495-01

Bearing, Ball, Retainer, Flanged

1

Inner Axis (Mod 22)

571-9439-01

Bearing, Ball, Retainer

1

Outer Axis

571-9445-01

Bearing, Ball, Annual, Flanged, Double Row

1

Outer Axis

526-1058-04

Shouldered Shaft

2

Rotor

571-9437-01

Bearing, Ball, Annual

4

Rotor

567-1312-01

Hex Nut

2

Rotor

536-1248-02

Spiral Flex, PWB (A2)

1

Outer Axis

 
At Duncan Aviation we do more than what is required; we do the right thing.

During a VG206D overhaul, Duncan Aviation replaces all of the above components. If we were to stop there, the overhauls would be correct according to maintenance manual requirements and the vertical gyro could be returned to service with no issues. This is where most component service facilities stop when overhauling a vertical gyro. Duncan Aviation doesn’t stop here. Twelve additional components, such as the Electrolytic Leveling Switches, are replaced. We do these, not so we can charge more, but because it is necessary and the right additional steps to take.

Electrolytic Leveling Switches


Example of damage caused by a blown Electrolytic Leveling Switch. Click to view image.

There are two electrolytic leveling switches inside your L-3 Vertical Gyro. These gravity-sensitive switches are sealed glass tubes partially filled with electrolytic solution and three electrodes. They are attached to the inner axis assembly via a bracket. They detect movement; one about the roll axis, the other the pitch axis.

The life cycle of these switches varies and depends on many factors, such as how many times the gyro gets powered up and how long the flights are. But the big factor is how long and many times the pilot uses the gyro fast erect switch. The point is this: the life cycle cannot be predicted, but when they blow, and they will, they explode with such force that glass shrapnel is thrown everywhere, damaging anything in its path. I’ve seen fragments destroy brackets and cut synchro or torque motor windings. Some of the most damage caused by an exploding switch are to the pitch shaft assembly (list replacement cost $1,100), pitch torque motor ($800) and roll synchro ($600). The damage can only be repaired with a complete overhaul of the unit.

Because of our years of knowledge and experience repairing the damage after an electrolytic leveling switch blows, we include its replacement as part of our overhaul. Doing only what is required is not always doing what’s right.

These are the additional Duncan Aviation components that are replaced during overhaul.

L-3 Part Number

Description

Quantity

Locations

561-1603-01

Switch, Electrolytic Leveling

1

Inner Axis

561-1601-02

Switch, Electrolytic Leveling

1

Inner Axis

MS16624-5018

Ring, Retaining

1

 

566-1103-01

Band, Sealing

1

 

573-1700-01

Tube, Evacuating

1

 

535-1508-01

Decal, Caution

1

 

535-1004-01

Decal, Instruction

1

 

S26100-01

Plate, Modification

1

 

S26100-02

Plate, Modification

1

Mod 22

535-1509-01

Decal, Direction

1

 

569-1307-01

Decal, Caution

1

 

535-1527-02

Label, Identification (J1)

1

 

These are overhaul components that we inspect for failure during an overhaul and will replace when necessary.

L-3 Part Number

Description

Quantity

Locations

JAN1N4148

Diode

2

Inner Axis

M39003/01-2587

Capacitor, Fixed

1

Inner Axis

550-1403-07

Capacitor, Fixed

1

Inner Axis

566-1071-02

Clamp, Spiral Flex

1

Outer Axis

566-1072-02

Clamp, Spiral Flex

1

Outer  Axis

535-1591-01

Plate, Identification

1

 

If you have questions about the overhaul of your L-3 Vertical Gyro, do not hesitate to contact a Duncan Aviation Avionics Tech Rep. To schedule your next VG overhaul, contact a Duncan Aviation Customer Account Rep.

Curt Campbell Avionics Tech Rep Lincoln, NE (LNK)
+1 402.479.4220
+1 402.416.8832

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