Learning Objective 021.11.03.02.08: State that a FADEC must have its own source of electrical power.

Note: This question requires further feedback, as currently we don't know which answer the examiner will accept as correct, and we are lacking slightly in the knowledge of which combinations of statements are given in the options. We have chosen the current option as the most likely to be considered correct, from our experience with similar questions, however, this has not yet been confirmed from the real exam, and as the actual answer to this is type specific, we can't be sure which the examiner would consider correct.

FADEC stands for Full Authority Digital Engine Control and is basically a digital control system that runs the whole engine management, all inputs and outputs. The FADEC has 2 independent Electronic Control Units (ECUs), or Electronic Engine Controllers (EECs) for redundancy, sometimes referred to as 2 "channels", with one "channel" always active and a second one on standby. If one channel fails, the other automatically takes control and performs the exact same functions. In addition to the ECU, all the FADEC peripherals such as actuators, solenoids, electrical wiring, sensors, and fuel metering are also part of the FADEC system and are used for control and monitoring.

Because FADEC is such an important system, and must therefore be fail-safe, it must have an independent power supply from the rest of the aircraft, which is usually a permanent magnet generator/alternator, as well as a backup power supply in case that fails. That could be a second FADEC specific generator, or sometimes, the FADEC system can also be supplied by the aircraft's normal AC system also (though that is not an option here at the moment), and sometimes this is the case for normal operations when the engine rotation is below a certain level, such as during engine start.

Here the aircraft battery may also have a back-up input into some of the important engine indications (N1, N2 and EGT on the B737 specifically), should AC power be unavailable during start. However, the aircraft battery will NOT run the FADEC system comletely on its own as it is a massive power drain and requires high voltage AC also, so is not part of a correct answer.

Therefore, as we know for sure that the examiner wants to see us answer that a FADEC system uses it's own permanent magnet generator/alternator, but that the battery is not a suitable back-up for the whole system (not on most jet aircraft anyway), we have said that only statement 4 is correct, given the current options.