Use a five-part model
1. Source
Identify where the system’s energy, pressure, or information originates: generator, battery, pump, compressor, reservoir, sensor, or computer.
2. Distribution
Trace buses, manifolds, lines, valves, relays, and control logic. Ask what separates normal, alternate, emergency, and standby paths.
3. Users
List the equipment supplied by that system. A failure question often tests a secondary consequence rather than the failed component itself.
4. Indications
Separate the physical failure from the cockpit indication. Determine what the crew would see first and which indications confirm or contradict the diagnosis.
5. Protection and backup
Identify automatic protections, isolation logic, redundancy, time limits, and the capacity of backup sources. Redundancy does not mean unlimited capability.
Common reasoning error
Students often memorize that a system has “two pumps” or “two generators” without asking whether each source can power every user, whether transfer is automatic, and whether the backup has a time or load limit. The operational answer usually depends on those conditions.