Tools of the Trade

Toos fo the Trade By Jim Sparks April 1999 Avisit to a well-equipped avionics shop can often be awe-inspiring. All of the various test equipment used to calibrate, repair, and certify a wide array of indicators and computers will leave most...

Toos fo the Trade

Avisit to a well-equipped avionics shop can often be awe-inspiring. All of the various test equipment used to calibrate, repair, and certify a wide array of indicators and computers will leave most maintenance technicians a bit bewildered. The majority of this highly sophisticated, high dollar shop equipment is just that — shop equipment needed by bench technicians. Line maintenance and troubleshooting avionic equipment can be accomplished using equipment that is readily available, and in many cases, moderately priced.

When considering what tool is right for the job, a general knowledge of the system in question is essential. In all cases, equipment or aircraft manufacturer's documentation should first be consulted. It is also advantageous to scan these documents for "CAUTIONS" or "WARNINGS." A caution is implemented to advise a technician of a possibility of equipment damage occurring unless procedures are closely followed. A warning is used when there is a chance of bodily injury to personnel.

The majority of recent aircraft incorporates digital technology in flight deck displays, navigation, communication, and auto flight systems. An advantage here is Built In Test Equipment (BITE). Should a malfunction occur in a BITE-equipped system, a diagnostic code is often provided to the technician that indicates where the fault occurred. The technician then replaces the defective Line Replaceable Unit (LRU). In some cases, the fault may be caused by a wiring problem, so assessing what test equipment to use is essential in completing a timely and effective repair. Aircraft that utilize analog systems and instruments also require selecting the proper diagnostic tools.

Technicians involved in flight line troubleshooting have to be quick to decide if the problem is related to a specific piece of equipment or if it is a problem with the aircraft.

Some safety measures include not using a damaged piece of equipment. Always inspect electrical leads for damaged insulation or exposed metal as well as electrical continuity. Any damaged test lead should be replaced. Be sure the device is in good operating condition and always make sure the proper range and function is selected prior to use. It is always advisable to avoid working alone when troubleshooting or testing electrical circuits.

A regulated power supply is an important component. It can be used to determine the operational status of numerous components and can often be constructed with off the shelf components from most retail electronics dealers. Several considerations are important in the purchase or construction of a power supply.

• Will the systems being tested require AC or DC power?
• What are the power requirements needed?
• What is an appropriate voltage and amperage range?
• How sensitive are the components being tested to spikes?
• Do filters need to be installed to cancel electrical noise?
• What sort of circuit protection is needed (fuse or circuit breaker)?

A power supply can be something as simple as a battery or as complex as a device with digital displays and multiple variable outputs. The use of an external voltage source will often enable the technician to make an accurate determination of its proper operation.

A Decade or resistance/capacitance substitution box is another tool that can be quickly installed to determine the operating capabilities of most systems sensors and can frequently be used in conjunction with a power supply.

Oscilloscopes (O' Scopes) are extremely versatile tools for the aviation industry. They provide the technician with the means of relating the electrical signal to time — that is to say they provide two dimensions to the circuitry being tested. Unfortunately, the new digital models can be quite expensive ($2,500 to $5,000) depending on the features needed. Analog units are much less ($500 to $700), and will provide the flight line technician with significant capabilities. An O' Scope can be used to monitor voltage levels and check frequencies of electrical signals. Also, when a unit with "Dual Trace" capabilities is used, multiple circuits can be monitored and compared.

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