Air India Flight 171 — Comprehensive Crash Analysis#

This report synthesizes all confirmed data, assumptions, and investigative hypotheses into a unified, logically structured analysis of Air India Flight 171 (Boeing 787‑8, VT‑ANB) which crashed shortly after liftoff from Ahmedabad on June 12, 2025. Each section clearly marks what is known, what is assumed, and what is hypothesized, and identifies required follow‑up data and tests.

1. Executive Summary##

Known:

AI171 departed Ahmedabad Runway 23 at 13:38 L (08:08 UTC), fully backtracked the 11,499 ft runway, rotated near runway end, climbed to ~425 ft AGL, then stalled and descended nose‑high into BJMC Hostel (~1 nm from runway) within 60 s. 241 of 242 onboard died, plus ground fatalities. RAT deployment and emergency lighting reported; FDR recovered, CVR pending.

Primary Hypothesis:

Abrupt, simultaneous loss of thrust on both GE GEnx‑1B67 engines—most likely due to a fuel‑related common‑cause—exacerbated by high density altitude and tight configuration margins.

Key Uncertainties:

Root cause of dual‑engine flameout (fuel contamination vs. control‑system fault vs. other).
Crew data‑entry and configuration accuracy.
Secondary system failures (hydraulic, electrical, avionics).

2. Environmental & Performance Context##

2.1 Meteorological Conditions (METARs)###

Time (UTC)	Temp / Dew (°C)	QNH (hPa)	Visibility	Notes
08:00 (120800Z)	37 / 16	1001	6000 m	Density altitude ≈ 3400 ft
08:30 (120830Z)	37 / 17	1000	6000 m	—
09:00 (120900Z)	38 / 18	999	6000 m	Highest temp & lowest pressure

Known: High temps (37–38 °C) + QNH drop (1001→999 hPa) yield density altitude ≈ 3500 ft, reducing both engine thrust and wing lift.

2.2 Weight & Configuration###

Load factor: 230/256 seats (93%) → near‑max takeoff weight.
Flaps/Slats: Likely set to 5°–15° for takeoff; autogap may extend slats at high AOA.
Thrust Derate & V‑Speeds: Dependent on accurate FMC entries of weight, temp, pressure. Errors here degrade climb performance.

Assumed: Crew entered correct weight/derate; flap/slat setting was standard. Verification requires dispatcher printouts and FMC logs.

3. Flight Timeline & Observations##

Phase	Time	Observations
Takeoff Roll	08:08:15	Engines set to takeoff thrust; full-length roll observed (FR24, CCTV).
Rotation (VR)	~08:09:05	VR reached near runway end; rotation slightly delayed.
Initial Climb (0–12s)	08:09:10	Airspeed decaying post‑VR; climb rate ≈0; gear remained down → partially forward tilt; RAT whine heard; cockpit/cabin lights flicker (emergency).
Mayday Call	~08:09:12	Pilot declared emergency immediately after liftoff (ATC logs).
Descent & Impact	08:09:27	Nose‑high descent at ~–475 ft/min; crashed into hostel building (~2 km from threshold).

Known: No positive climb; immediate declaration of emergency; onset of RAT and emergency lighting.

Assumed: Mayday indicated thrust loss; CVR will confirm exact phrasing and warnings.

4. Systems Examination##

4.1 Propulsion System (GEnx‑1B67)###

Service History (Known):

Ice‑crystal flameouts at cruise addressed via FADEC VBV cycling (2013).
Fan mid‑shaft cracks found in test stand failure; inspected and recoated (2012).
Fuel manifold leaks fixed by redesigned components and FAA ADs (2018–21).

Hypothesized Failure Modes:

Fuel Contamination Surge: Water/DEF/microbial contamination → rapid compressor surge and near‑instant dual flameout, akin to—but faster than—Cathay 780. Supported by loud bang reports and simultaneous N1/N2 drop (FDR).
FADEC/Common‑System Fault: Rare software or sensor anomaly commands thrust rollback on both engines. DGCA has called for FADEC diagnostics.
Avionics/Electrical Event: Battery or bus fault (2013 Dreamliner fire risk) could disrupt engine controls and hydraulics. Survivor’s light flicker hints at power transfer.
Bird/FOD Strike: Dual ingestion improbable—no video evidence, no smoke/backfire observed.

4.2 Hydraulic & Electrical Systems###

Hydraulics: Engine‑driven pumps lost with engine spool‑down; RAT supplies limited hydraulic pressure; partial gear retraction indicates hydraulic loss during sequence.
Electrical: Loss of main generators triggers RAT and emergency power; cabin lights flickering consistent with bus transfer and RAT operation.

Assumed: Hydraulic failure is secondary to engine shutdown, not primary.

5. Crew & Operational Factors##

Crew Experience: Captain (8,200 h), FO (1,100 h), both trained on 787.
Take‑off Configuration Warning: 787’s TO CONFIG alerts for flap/slat/gear/trim mismatches; must investigate if warning sounded (CMC logs).
Crew Workload: <1 min for diagnosis and action at low altitude; pilot reactions constrained by timing.
Mayday Transmission: Indicates rapid recognition of catastrophic failure.

Assumed: Crew followed standard procedures until engine failure.

6. Comparative Case Studies & Lessons##

Cathay Pacific 780 (2010): Dual rollback from contaminated fuel; prolonged partial power loss.
BA 38 (2008): Double FOHE icing; progressive thrust loss on final.
Air Transat 236 (2001): Fuel exhaustion; successful glide to landing.
US 1549 (2009): Dual bird strike; controlled ditching by A320.

Insight: Dual engine failures nearly always share a common cause (fuel or environmental); independent failures extremely rare.

7. Hypothesis Scenarios & Evidence Matrix##

Hypothesis	Supporting Data	Contradictory Data	Tests/Data Needed
A. Fuel Contamination Surge	Loud bang reports; simultaneous N1/N2 drop; DGCA focus on fuel testing; no pre‑impact smoke/fire	No prior airport fuel‑system water reports; rapid onset may challenge microbial growth timeline	Fuel lab analysis; FDR fuel flow/temperature; CMC contamination alerts
B. FADEC/Common‑System Fault	RAT deployment; DGCA FADEC diagnostics	No known FADEC AD; very low probability of identical dual fault	Extract FADEC event logs; review recent software updates
C. Avionics/Electrical Event	Lights flickering; possible fire warning	No smoke/fire visible on video; likely audible CVR alarms	CVR smoke/fume alarms; avionics maintenance records
D. Bird/FOD Strike	Takeoff environment may have birds	No bird flocks or ingestion noise; no cockpit bird warnings	CVR bird-strike aural alerts; FDR EGT/vibration spikes
E. Configuration Error	Late rotation; marginal performance observed	No TO CONFIG warning sighted; slats observed extended; single-engine climb capability would remain	CMC TO CONFIG logs; FDR flap/slat handle positions

Interpretation: Hypothesis A is most probable given evidence and historical parallels; B/C plausible; D/E unlikely as sole causes.

8. Investigation Priorities & Next Steps##

Black Box Examination:
- FDR: thrust lever angles, N1/N2, fuel flow, hydraulic pressures, gear handle, slat/flap positions.
- CVR: Mayday transcript, cockpit warnings (stall, fire, config), crew callouts.
Fuel Quality Testing:
- Lab tests for water, microbial content, DEF or additives in fuel uplifted to VT‑ANB and storage.
CMC & Maintenance Logs Review:
- TO CONFIG warning events; fuel contamination or nozzle actuator faults; FADEC and avionics fault logs.
Hydraulic/Electrical Analysis:
- RAT deployment timing; accumulator pressure trends; hydraulic actuator command attempts.
Human Factors Assessment:
- Crew dispatch data entry validation; training records for emergency dual-engine scenarios;
- Interview of sole survivor for any additional cues (sound, smell, warnings).

9. Conclusion##

AI171’s crash stems from a near-instantaneous, dual-engine thrust loss at low altitude under high-density altitude and near‑max weight. While configuration errors and environmental factors tightened margins, the preponderance of data points to a fuel‑related common‑cause or rare control‑system anomaly. Confirming the root cause requires integrated analysis of FDR/CVR data, fuel lab results, and system logs. Findings will guide regulatory actions—whether on fuel handling, FADEC software, or operational procedures—to prevent recurrence and maintain the 787’s exceptional safety record.