CHAPTER 10: IGNITION SYSTEMS - Key Concepts

A set of Q&A flashcards covering magneto ignition, timing, dual ignition, starting with impulse coupling, and the shift toward electronic ignition and FADEC, including safety considerations and notable incidents.

What is the primary purpose of the aircraft ignition system in a spark-ignition engine?

To deliver an electrical current to each spark plug at the correct time to ignite the fuel–air mixture and produce the power stroke.

Why do piston-engine aircraft often use magneto ignition?

Because magnetos are independent of the aircraft's electrical system and will continue to operate if the aircraft's electrical system fails.

Do compression-ignition engines require an ignition system?

No. They do not use spark plugs and do not rely on a traditional ignition system.

What are the key components of a magneto ignition system?

Magneto, distributor, high-tension leads, spark plugs, and an ignition switch.

How does a magneto generate high-tension electrical current?

A magnet spinning relative to a conductor within the magneto creates a changing magnetic field that induces a high-voltage current via electromagnetic induction.

What is the role of the distributor in a magneto ignition system?

To distribute the high-tension current to each spark plug and ensure the spark occurs at the correct time, just before the power stroke.

What did the August 8, 2008 Cessna 207 incident illustrate about spark timing?

Incorrect timing (50–60 degrees before TDC instead of about 22 degrees) can cause pre-ignition, detonation, high cylinder temperatures, and power loss.

What hazard can damaged high-tension leads pose?

Breakdown can allow high voltage to arc to other parts of the aircraft, compromising ignition and posing a hazard to occupants.

Where is a spark plug located and how does it ignite the mixture?

In the cylinder head; current jumps across the two electrodes at the tip to ignite the fuel–air mixture.

What is the purpose of having a dual ignition system?

Two independent magneto systems; each cylinder has two spark plugs powered by separate magnetos to provide redundancy and better combustion.

How is the magneto ignition switch typically used in flight?

Five positions: OFF, R (right), L (left), BOTH, START; R or L selects a single magneto to run; BOTH runs both magnetos; START engages the starter.

What is the expected effect on engine rpm when switching from BOTH to RIGHT or LEFT during preflight checks?

A small rpm drop is expected; the amount is specified in the Pilot Operating Handbook.

What should you infer if the engine stops when one magneto is selected or experiences no rpm drop when switched off?

A fault in the ignition system; the engine should not be flown.

How does an impulse coupling assist starting the engine?

During starting at low rpm, it retards the magnet, winds a spring, and just before the power stroke releases the magnet to generate a strong spark.

What is FADEC and how does it relate to ignition systems?

FADEC is a Full Authority Digital Engine Control that manages engine and propeller with a digital computer; it can improve efficiency but creates dependence on electronics, often with redundancy and backup power.

What accident highlighted the need for backup power for FADEC systems?

The 2007 Diamond DA42 accident in Germany, where a flat battery caused both ECUs to fail during takeoff, leading to a belly landing and underscoring the importance of backup power.

What are the advantages of electronic ignition systems over traditional magnetos?

Fewer moving parts, potential for a more powerful spark, and timing/duration control that can adapt to flight conditions for a cleaner burn and better efficiency.

What is the effect of electronic ignition on engine performance?

Cleaner burn, improved power output and fuel efficiency; timing can be optimized for current flight conditions.

What is the general maintenance guidance for ignition systems?

Remain alert for malfunctions and never operate an aircraft with a faulty ignition system; perform preflight checks including magneto checks.

What happens inside the spark plug to ignite the mixture?

Electrical current jumps across the electrodes at the plug tip inside the cylinder, igniting the fuel–air mixture.