40 Questions
What is a common feature of most instruments in a GA cockpit?
A flange with screws at each corner
How are some instruments mounted in a GA cockpit?
Fitted into clamps with no flanges
What is the advantage of clamped instruments in a GA cockpit?
They can be removed from the front of the panel
What should be done to remove an instrument from a clamp in a GA cockpit?
Loosen the clamping screws, then loosen the clamp from the panel
What might happen if the clamp is unscrewed from the panel first when removing an instrument?
The instrument will fall behind the panel, making it difficult to remove
What do the horizontal arrows point to in the picture above?
The mounting screws
What is Avionic Troubleshooting Techniques related to?
Aviation maintenance tasks
What is a key aspect of aviation maintenance?
Consisting of many separate tasks
What is a crucial precaution when handling electronic components?
Avoiding contact with the pins or sockets
What should be done to an aircraft prior to removing ESD sensitive equipment?
Powering it off and grounding it
What is the purpose of fitting conductive covers/caps to disconnected plugs?
To protect the plug from ESD damage
What is the function of the avionics equipment rack in an aircraft?
To supply cooling and electrical connection to the rest of the aircraft
What is the purpose of the key pins on the connector block of the avionics rack?
To ensure the correct LRU is connected to the rack
What is the primary function of the screw latch at the front of the LRU?
To secure the LRU to the avionics rack
What should be done to the equipment metal case before disconnecting cables?
Touching the equipment metal case to equalize electrostatic potential
What is the purpose of touching the plug outer shell to the outer shell of the equipment mating connector?
To equalize electrostatic potential
What is a necessary step to undo bayonet connectors?
Pushing them in before turning
What is the purpose of a ratchet and sprung pawl in some threaded connectors?
To prevent vibration from loosening the connector
Why is copper wire used for safety wiring?
Because it can be broken in an emergency
What is the purpose of safety wiring on connectors without a positive locking device?
To prevent inadvertent disconnection
What is the primary concern when handling electrostatic sensitive devices?
Electrostatic discharge damaging the device
In what type of aircraft might safety wiring be used to secure guarded switches?
Military aircraft
What is the size range of copper safety wire?
15-32 thousandths of an inch
Where can more information about ESD safety precautions be found?
In Module 5
What can be a result of removing and refitting an LRU, even if it is not faulty?
The connection between the pin and socket may be re-made, potentially repairing a fault
What is a method of confirming a faulty component?
Swapping the component with a spare from a duplicate system
Why might swapping a faulty LRU with a spare from a duplicate system be less attractive for computerized parts?
It may require software changes
What should be done to every system that has a wire in the connector?
It should be tested to identify and test induced faults
What should be done with the paperwork when a faulty part is identified?
It should be updated
What should be done with the spare part after confirming the fault?
It should be fitted to the duplicate system
What is a risk when moving a faulty LRU from one system to another?
It may cause damage to the originally serviceable second system
What is essential for every step carried out during troubleshooting?
It should be documented
What is the common outcome when an avionics LRU is removed from an aircraft due to a fault and then tested in a workshop?
No fault is found
What is the primary cause of NFFs (No Fault Found) according to the text?
Poor troubleshooting techniques
What is a 'rogue' unit in the context of avionics LRUs?
A unit that repeatedly fails functional tests in the aircraft but passes tests on the bench
What is a heuristic in the context of troubleshooting?
A rule-of-thumb for problem-solving
What is a Consistent Fault Set (CFS)?
A set of all possible failures that can reasonably explain a given set of trouble symptoms
What is a potential consequence of NFFs (No Fault Found)?
Expensive delays or flight cancellations
Why is it important to have good troubleshooting techniques?
To reduce the number of NFFs
What is the typical strategy used in troubleshooting?
Heuristics and step-by-step procedures
Study Notes
Bayonet Connectors and Threaded Connectors
- Bayonet connectors must be pushed in before they can be turned to undo them.
- Some threaded connectors have a ratchet and sprung pawl to counter vibration.
- Threaded connectors without a positive locking device must be wire locked in a similar manner to a bolt.
Wire Locking Connector
- Care must be taken with terminology, as some American texts refer to stainless steel wire locking as safety wiring.
- In our context, safety wire is 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.
- Copper wire will stop vibration or crew inadvertent disconnection, but can be broken in an emergency to disconnect the connector without tools.
Electrostatic Sensitive Devices (ESD) Precautions
- Do not touch pins of any electronic component.
- Do not touch sockets or pins within the plugs of any electronic equipment.
- When removing ESD-sensitive equipment from an aircraft, the aircraft must be grounded, and power removed.
- Prior to disconnecting cables, personnel shall touch the equipment metal case to equalize any electrostatic potentials.
- Immediately fit conductive covers/caps to disconnected plugs.
Avionics Component Installation
- Avionics equipment racks in the aircraft provide the Line Replaceable Unit (LRU) with rigid mounting to withstand G-forces and vibration.
- The racks supply cooling and electrical connection to the rest of the aircraft.
- In modern transport category aircraft, the mounting restraint comes from tapered pins on the rack and alignment holes at the back of the LRU.
- A screw latch at the front of the LRU secures it to the rack.
- The connector block on the back of the rack has a set of key pins to ensure the wrong LRU is not connected in the wrong place.
Instrument Mounting
- The majority of instruments may have a flange with a screw at each corner.
- Some instruments are fitted into clamps and have no flanges of their own.
- Clamped instruments can be removed from the front of the panel without dropping the panel or loosening the clamp.
- To remove the instrument, the clamping screws are loosened, then the instrument can be withdrawn from the panel, and electrical connectors disconnected.
Avionic Troubleshooting Techniques
- Defect Prevention is crucial in avionics maintenance, as No Fault Found (NFF) components can be costly and time-consuming to remove and test.
- NFFs can cause expensive delays or flight cancellations, and may be a major proportion of components sent to workshops for inspection.
- Poor troubleshooting techniques are a major cause of NFFs, highlighting the importance of training.
Troubleshooting Terminology
- Heuristics are rules-of-thumb useful for problem-solving.
- A Consistent Fault Set (CFS) is a group of all possible failures that can reasonably explain a given set of trouble symptoms.
- Once the faulty part is identified, it must be replaced, and paperwork brought up to date.
- Confirming a faulty component can be done by using a spare already on the aircraft, if applicable.
This quiz covers the proper procedures for securing connectors in aerospace maintenance, including bayonet and threaded connectors.
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