Likely Sequence of Events - AI171.

Further to my earlier posts , here is a continuation of my independent, unofficial deep-dive analysis. This presentation below that follows in next comment involves an even more granular FIFO/LIFO–based review of data and event sequences, considering multiple pathways, architectural fail-safes & redundancies as well as cross-checks, synergised seamlessly with the AAIB preliminary report, UTC timestamps, and the data available across the public domain — thus likely reaching a high-fidelity accuracy in reconstructing the probable sequence of events.

In subsequent comment post below, I have outlined the highly probable sequence of events on AI171, with precise timestamps — in the hope of keeping this tragedy in sight and ensuring we never lose focus on what truly matters.

This is a purely personal, independent unofficial granular-level analysis prepared for knowledge-sharing with peers. Hoping experts, engineers, aero techs and enthusiasts find it worth a read. — together, we can continue striving toward safer skies.

Likely Sequence of Events - AI171.

1. Lift-off: 

Aircraft lifts off; engines at normal climb power, FSOVs obviously OPEN (in RUN) (energized solenoids); electrical buses normal. – 08:08:39 UTC 

2. Likely Sudden Electrical cascade / total power failure: 

Rapid electrical fault causes AC/DC buses to collapse; Engines VFSG's (Generators) lose output. 

RAT deploys automatically into the airflow midstream to provide emergency power. – 08:08:40–41 UTC (ESTIMATED) (AAIB Prelimnary report(PR) confirms: deployed immediately after lift-off) (Page 15)

3. FSOV solenoids respond to power loss. Solenoids enter fail-safe mode instantly as they get de-energized → The spring closes valve. → Fuel cutoff occurs almost immediately.

Both engines starve → dual flameout. 

Engine 1 FSOV cutoff – 08:08:42 UTC

Engine 2 FSOV cutoff – 08:08:43 UTC 

4. Hydraulics supply restoration via RAT 

AAIB PR confirms Hydraulics stabilizes first, enabling flight controls and essential 

systems. – 08:08:47 UTC 

5. Essential AC/DC buses restored (RAT emergency power) – 08:08:52 UTC (Est.) 

6. FSOVs move back to OPEN (recorded as RUN), either via: 

 Option A: Pilot manually moves cockpit switches once buses are live. (Less Likely) 

Option B: Automatic FADEC logic restores FSOVs to OPEN/ RUN and 

 initiates engine spool-up / relight. (More Likely)

• Recorded FDR timestamps: 

 Engine 1 FSOV OPEN / RUN – 08:08:52 UTC 

 Engine 2 FSOV OPEN/ RUN – 08:08:56 UTC

4-second difference explanation: If pilot manually moved switches, both would likely be moved almost simultaneously unless distracted or delayed.(Distractions/ Delays highly unlikely for experienced pilots). Appears Automatic relight sequence.

•Automatic FADEC Relight- logic scenario: IN THAT CASE: FADEC logic for FSOV RUN restoration could inherently sequence commands separately: 

 Engine 1 logic triggers as soon as bus power is available. 

 Engine 2 logic may follow after a pre-programmed interlock, spool-up 

 check, or stabilization delay. 

This would naturally produce a 4-second stagger between FSOV OPEN (recorded as RUN ) for the two engines. Highly likely in modern 787 architecture, especially during backup power recovery and engine auto-relight sequences. 

7. Probability of cause for initial fuel cutoff 

Initial fuel cutoff likely occurred immediately after total power loss/RAT deployment. 

Cockpit switches cannot actuate FSOVs without availaibility of power; (motor-driven actuators cannot fail-safe under total power loss so that is practically ruled out) 

Hence, FDR-recorded fuel cutoff most likely reflects fail-safe solenoid closure triggered by total power loss, not pilot action. 

8. Sequence

Lift-off → total power loss → RAT deployment → FSOV closure → fuel cutoff → dual engine flameout → hydraulics supply restoration (RAT) → AC/DC bus restoration → FSOVs return to OPEN (recorded as RUN )(manual(less likely) or FADEC (most likely) , with 4-sec stagger.

DISCLAIMER : This is a purely personal, independent unofficial analysis prepared for knowledge-sharing amoung aviation community. Final Investigations and findings rest with investigating authorities like AAIB and the DGCA. Greatful for going through.