Tunnel Vision in Troubleshooting

Bayonet Connectors

• Bayonet connectors must be pushed in before turning to undo them.
• Some threaded connectors have a ratchet and sprung pawl to counter vibration.
• Connectors without a positive locking device must be wire locked in a similar manner to a bolt.

Wire Locking

• Care must be taken with terminology, as some American texts refer to stainless steel wire locking as "safety wiring".
• In our context, "safety wire" refers to copper lock wire, available in sizes from 15-32 thousandths of an inch (thou).
• Copper safety wire is used for connectors without a positive locking device that must be undone in an emergency.
• The reason for copper is that it stops vibration or crew inadvertent disconnection, but can be broken in an emergency to disconnect the connector without tools.

Electrostatic Sensitive Devices (ESD) Precautions

• ESD safety precautions are covered in Module 5.
• A general guide to the safe handling of ESD includes precautions to avoid damage.

Built-In Test Equipment (BITE)

• BITE describes a range of equipment, from simple to complex systems.
• Simple BITE allows a technician or flight crew member to perform a "go/no-go" self-test on a specific module.
• More sophisticated BITE systems allow a technician to perform tests with built-in switches and indicators on a module.
• The most sophisticated BITE systems record performance information over a number of flight legs, diagnose failures, and display specific instructions to engineers on how to repair the system.

Troubleshooting Flow Charts

• A troubleshooting flow chart is a printed or computerized chart that directs the maintenance technician along a logical testing and diagnosis path for a particular system.
• The flow chart branches to another test or conclusion based on the test results.
• A flow chart can be characterized as a series of "if-then" statements.

No Fault Found (NFF)

• Repairing or replacing avionics components is not the biggest cost in maintenance.
• Avionics do not wear out regularly, but break down unexpectedly.
• Unexpected maintenance is more expensive than scheduled repairs.
• NFF is a maintenance problem where a fault is not found, leading to frustration and increased costs.

Tunnel Vision

• Tunnel vision is a mindset where a technician sees a situation as though through a tunnel, focusing on one direction and ignoring conflicting information.
• In the maintenance domain, tunnel vision is a well-known occupational hazard.

Half-Split Test

• Theoretically, the most efficient test is the one that provides the most information.
• A half-split test is a test that eliminates roughly half the items from a set of possibly failed components.

Test-Induced Failure

• When testing a system or component, there is a probability that the test will cause a failure.
• Test-induced failures are safety risks only when they remain undetected.
• Examples of test-induced failures include bending a pin when reconnecting a connector, or causing a voltage spike when testing a subsystem.

Half-Split Mindset

• The best model for troubleshooting is to see the system as a set of problems to be solved.
• The problem/solution mindset is critical in understanding how equipment works and how to troubleshoot it.
• Understanding the function being solved, how errors affect other parts, and the implementation of each solution helps in troubleshooting.

Confirming a Faulty Component

• Another method of confirming a faulty component is by using a spare already on the aircraft.
• The spare part can be moved into the faulty system and tested to confirm the system is now serviceable.
• The replacement part can then be acquired from stores, fitted, and tested.
• This method is suitable for non-computerized parts, but computerized parts may require software changes before they can work in the new position.