NEW SEVENTH PLAUSIBLE HYPOTHESIS THAT DESERVES LINE OF ENQUIRY — Cockpit Fuel Control Switches Logic Ambiguity During Electrical Transience.

✈️AI171 : Keeping the Memory Alive, Honouring the Lives Lost ✈️

Dear Aviation Professionals, Aero Engineers, Technicians and Enthusiasts. Greetings. As you may be already aware , there are total six plausible pathways/hypothesis that has been researched and identified after an in-depth deep-dive analysis and a granular event timelines including FIFO/LIFO technical evaluations. While engaging in some recent technical exchanges among the community peers, especially with professional who goes by pseudonym @Corwin4000 a new technically credible line of reasoning has emerged — one that merits inclusion as the seventh likely root cause hypothesis for the AI171. This perspective centers on a transient electrical / logic-level fault causing the Fuel Control Switch discretes to be momentarily read as “CUTOFF” even without manual lever movement . due to loss or corruption of valid-state continuity in the RDC (Remote Data Concentrator) interpretation logic or its validation logic faiing to sense, or may interpret as unavailable, the incoming signal, during a power transience event. This newly articulated hypothesis proposes that a momentary logic-level ambiguity could, via FADEC , trigger a dual fuel cutoff command through its programmed fail-safe de-energization response. This could occur entirely without any pilot input and without physical actuator de-energization or FSOV snap-shut at the spar level. As some independent circuit diagrams, notably by Jeremy J. Thompson (with due respects and acknowledgement) indicate, each switch may have both RUN and CUTOFF throws actively powered — i.e., one line energized at RUN, another at CUTOFF. If both signals were simultaneously lost (due to a bus undervoltage or transient dip), the RDC would logically interpret that as a “transition” or “invalid” state.

The fail-safe interpretation in such a scenario defaults to Fuel Shutoff thus effectively mimicking a commanded CUTOFF, even if no pilot physically moved the lever. The Fuel Control Switches provides analog position signals to a Remote Data Concentrator (RDC). The RDC digitizes the switch position into logic bits and transmits them to: Both FADEC channels (Channel A & B), The EICAS and the The Central Maintenance Computer (CMC).

Now, If a transient electrical disturbance, bus glitch, or data corruption occurs resulting in lost, invalid, or ambiguous readings ,even for a few milliseconds — the FADEC’s input validation logic may fail to sense, or may interpret as unavailable, the incoming RUN signal. In such a case, it would default to its programmed fail-safe state, terminating fuel flow at the FMU servo valve (Fuel Metering Unit) instantly halting fuel flow to the engines. This response is instantaneous and independent of switch movement / FSOV actuator power—representing pathway: Switch sensor -->RDC -->FADEC.

Thanks