ACS Fuel Systems & Aircraft Plumbing 2 — Questions and Answers
Question 1: What is the purpose of a fuel crossfeed system on a multi-engine aircraft?
- To feed both engines from either tank to manage fuel load or feed a live engine from any tank after an engine failure (Correct answer)
- To transfer fuel only to the landing gear hydraulic reservoir
- To dump fuel overboard in an emergency
- To preheat fuel in cold weather
Correct answer: To feed both engines from either tank to manage fuel load or feed a live engine from any tank after an engine failure
A crossfeed system allows either engine to draw from any tank, balancing fuel loads and enabling a surviving engine to draw from the opposite side's tank after an engine failure.
Question 2: Aircraft fuel quantity gauges are required by FAR to be accurate to within what tolerance?
- ±5% of total capacity
- They must only be accurate when reading empty (zero fuel) (Correct answer)
- ±10% of indicated reading at all fuel levels
- No tolerance is specified — they are advisory only
Correct answer: They must only be accurate when reading empty (zero fuel)
FAR 23.1337 requires fuel quantity gauges to be accurate only at the empty (zero) position; at all other quantities, accuracy is advisory and may vary.
Question 3: What type of material is prohibited for use in aircraft fuel system tubing due to incompatibility with aviation fuels?
- Aluminum alloy 5052
- Galvanized steel tubing (Correct answer)
- Stainless steel
- titanium
Correct answer: Galvanized steel tubing
Galvanized steel is prohibited in fuel systems because zinc from the galvanizing reacts with tetraethyl lead in AVGAS to form lead compounds that clog filters and damage fuel system components.
Question 4: When is it mandatory to bond and ground an aircraft during fueling?
- Only when fueling turbine aircraft
- Always, before fueling begins, to prevent static discharge ignition of fuel vapors (Correct answer)
- Only when fueling in dry climates with low humidity
- Grounding is optional if fueling from a bonded fuel truck
Correct answer: Always, before fueling begins, to prevent static discharge ignition of fuel vapors
Bonding and grounding are always required before fueling to equalize static electrical charges and prevent sparks that could ignite fuel vapors.
Question 5: What is the correct tube material for a high-pressure aircraft fuel line (above 1,500 PSI)?
- Aluminum alloy 5052-O
- Corrosion-resistant steel (CRES / stainless steel) or titanium (Correct answer)
- Copper tubing
- Rigid PVC tubing
Correct answer: Corrosion-resistant steel (CRES / stainless steel) or titanium
High-pressure fuel lines require CRES (stainless steel) or titanium tubing for the strength and corrosion resistance needed at pressures above 1,500 PSI.
Question 6: A flexible fuel hose assembly should be replaced if it shows:
- Any slight surface scuffing on the outer cover
- Blistering, cracking, collapse under load, or has exceeded its calendar life limit (Correct answer)
- Minor discoloration from fuel residue
- Manufacturer's label becoming difficult to read
Correct answer: Blistering, cracking, collapse under load, or has exceeded its calendar life limit
Flexible hoses must be replaced if they exhibit blistering, cracking, inner tube collapse, chafing through to reinforcement, or if the calendar service life has expired.
ACS Fuel Systems & Aircraft Plumbing 2
What is the purpose of a fuel crossfeed system on a multi-engine aircraft?