Diagnostic and Testing Tools Flashcards

A technician connects a data bus analyzer to an ARINC 429 bus. The analyzer shows no valid words being decoded. Which condition is least likely to cause this?

Answer: The transmitting LRU is in normal operational mode

A transmitting LRU in normal operational mode should be producing valid data; the other options would all prevent proper decoding.

During a functional test of an aircraft autopilot servo, a technician monitors servo current with a current probe. Unexpectedly high current during light mechanical load most likely indicates:

Answer: Mechanical binding or a failing servo motor winding

Excessive current under light load suggests the motor is working harder than expected due to internal mechanical friction or a shorted winding.

When using a pitot-static test set to perform an altimeter check, the technician must ensure the aircraft's static system is:

Answer: Leak-free, as leaks will cause the altimeter to read incorrectly

Any leak in the static system will allow ambient air to enter, preventing the test set from maintaining the correct simulated altitude.

Which oscilloscope control is adjusted to stabilize a repetitive waveform so it appears stationary on the screen?

Answer: Trigger level and source

The trigger circuit synchronizes the sweep start to a selected point on the waveform, causing successive cycles to overlap and appear stationary.

A technician is testing an aircraft bonding connection and measures 0.003 ohms. Per FAA guidance, this reading is:

Answer: Acceptable; bonding resistance should typically be 0.003 ohm or less

FAA AC 43.13-1B specifies that bonding resistance should generally not exceed 0.003 ohm for structural and electrical bonding.

A ramp tester for an ILS localizer system provides test signals to the aircraft's nav receiver. After tuning the receiver, the CDI needle deflects fully left and does not center. This most likely indicates:

Answer: A fault in the receiver's deviation output circuit or a course deviation signal is being injected

A ramp tester injecting an on-course signal should produce a centered CDI; full deflection suggests the receiver or its deviation output is faulty.

Which of the following test equipment is specifically designed to verify the accuracy of an aircraft's transponder Mode C altitude encoding?

Answer: Pitot-static test set used in conjunction with an encoding altimeter check

Mode C altitude encoding is verified by applying known simulated altitudes via a pitot-static test set while monitoring the transponder's Gillham code output.