AMT Reciprocating Engine Ignition Systems 2 — Questions and Answers
Question 1: What is the primary purpose of the impulse coupling on a magneto?
- Increase magneto output voltage at high RPM
- Provide a retarded and intensified spark during engine starting (Correct answer)
- Reduce magneto speed to match crankshaft speed
- Protect the magneto from voltage spikes
Correct answer: Provide a retarded and intensified spark during engine starting
The impulse coupling temporarily retards ignition timing and snaps the magnet past the neutral position to produce a strong spark at low starting speeds.
Question 2: Which ignition system component prevents a spark plug from firing at the incorrect time due to residual magnetism?
- Condenser (Correct answer)
- Primary coil
- Breaker points
- Distributor rotor
Correct answer: Condenser
The condenser absorbs the collapsing magnetic field energy, preventing arcing at the breaker points and ensuring sharp primary circuit cutoff.
Question 3: On a dual-magneto ignition system, the 'BOTH' position on the ignition switch is used during normal flight because it:
- Reduces fuel consumption by providing complete combustion (Correct answer)
- Allows crosschecking of magneto operation in flight
- Is required by FAA regulation at all times
- Prevents spark plug fouling from lead deposits
Correct answer: Reduces fuel consumption by providing complete combustion
Firing two spark plugs per cylinder from separate magnetos produces more complete combustion, improving efficiency and providing redundancy.
Question 4: A magneto's 'E-gap' refers to the position of the rotating magnet when:
- The breaker points are fully closed
- Magnetic flux through the coil core is changing most rapidly (Correct answer)
- The distributor finger aligns with the next electrode
- The magneto reaches its maximum RPM
Correct answer: Magnetic flux through the coil core is changing most rapidly
E-gap (efficiency gap) is the rotor position at which flux change in the core is at maximum, generating the highest possible primary voltage before points open.
Question 5: What type of spark plug would most likely be used in a high-compression aircraft engine to resist fouling?
- Long-reach, cold heat range plug
- Short-reach, hot heat range plug
- Long-reach, hot heat range plug
- Short-reach, cold heat range plug (Correct answer)
Correct answer: Short-reach, cold heat range plug
Short-reach, cold heat range plugs transfer heat away quickly, reducing pre-ignition risk in high-compression engines while the short reach avoids interfering with pistons.
Question 6: During a magneto check at runup, a drop of more than the manufacturer's specified RPM when switching to one magneto indicates:
- Normal single-magneto operation
- A possible defective magneto or fouled spark plug on that side (Correct answer)
- The need to adjust ignition timing
- Excessive advance in the magneto timing
Correct answer: A possible defective magneto or fouled spark plug on that side
An excessive RPM drop on one magneto suggests that magneto or its associated plugs are not functioning correctly, requiring maintenance investigation.
Question 7: Which of the following describes correct procedure when grounding a magneto for maintenance?
- Connect the P-lead to aircraft structure to disable ignition output (Correct answer)
- Remove the magneto coil from the housing before any work
- Disconnect the high-tension leads and leave P-lead connected
- Short the secondary coil to the magneto case
Correct answer: Connect the P-lead to aircraft structure to disable ignition output
The P-lead grounds the primary circuit through the ignition switch; ensuring it is connected to ground (switch OFF or lead grounded) disables the magneto safely.
AMT Reciprocating Engine Ignition Systems 2
What is the primary purpose of the impulse coupling on a magneto?