CASE 011
:
THE CASE OF FLIGHT 417
Flight 417 touched down in the grass beside the runway. Ninety-four passengers evacuated. The pilots say the aircraft was pushed sideways by invisible forces. The instruments showed nothing unusual. The airport reported moderate winds. Someone — or something — is not telling the whole story.
CASE BRIEFING
At 7:52 PM on a Tuesday evening in October, Flight 417 — a regional jet operating for Meridian Airways — was established on final approach to Runway 24 at Hartwell International Airport.
The flight had been routine.
Departure from Cranfield City Airport at 6:34 PM. Cruise altitude 18,000 feet. Descent commenced on schedule. Weather at Hartwell reported as acceptable — wind 210 degrees at 12 knots, visibility good, cloud base 2,400 feet. Nothing that should have concerned an experienced crew.
Captain Elena Vasquez, 47, had 14,000 hours of flying experience. First Officer Daniel Osei, 31, had 3,200 hours. Between them they had flown this approach dozens of times.
At approximately 400 feet above the runway — less than ninety seconds from touchdown — Captain Vasquez noticed something wrong.
The aircraft was pointing directly at the runway centreline. The instruments confirmed it. But through the windscreen the runway was moving — sliding steadily to the right as though the aircraft was being pushed sideways by a force neither pilot could see or feel.
"Four-one-seven, we have an unusual drift situation," Captain Vasquez transmitted to approach control. "We appear to be tracking right of centreline despite correct heading."
Approach control responded immediately. "Four-one-seven, wind is two-one-zero at twelve. Previous traffic reported no anomalies."
At 200 feet Captain Vasquez made a correction — applying left rudder and banking slightly left to bring the aircraft back toward the centreline.
It was not enough.
The aircraft crossed the runway threshold 40 metres to the right of the centreline and 60 metres short of the paved surface. The right main landing gear struck the grass verge at the runway edge. The nose gear followed a fraction of a second later on uneven ground. Both collapsed under the impact load. The aircraft slid for 180 metres on its belly before coming to rest partially on the runway edge, partially on the grass.
The evacuation began within 22 seconds of the aircraft stopping.
All 94 passengers and 6 crew members evacuated via emergency slides.
Eleven passengers sustained minor injuries — sprains and bruises sustained during the evacuation. No fatalities. No serious injuries.
The aircraft — a seven-year-old regional jet with 18,400 flight hours — was destroyed beyond economic repair.
By 8:30 PM the Aviation Accident Investigation Bureau had been notified. By 10:00 PM their lead investigator — Dr. Marcus Webb — had arrived at the scene.
He stood at the point where Flight 417's right main gear had first touched the grass and looked back along the approach path.
Captain Vasquez had given him her account in the airport medical centre — still in her uniform, a cut on her forehead from the evacuation slide.
"I was pointing at the runway," she said. "The whole time I was pointing at the runway. Something pushed us sideways. I have never experienced anything like it in 14,000 hours."
The airline's operations director had given a more cautious account to journalists outside the terminal.
"We are cooperating fully with the investigation. It would be inappropriate to speculate about causes at this stage."
Three preliminary explanations were circulating among the investigation team before the night was out.
Pilot error — a misjudged approach that the crew failed to correct in time.
Navigation or flight control fault — a system failure that caused the aircraft to drift without the crew's awareness.
A weather event — a localized wind phenomenon that was not detected by the airport's surface weather systems and was not present when the previous aircraft made the same approach eleven minutes earlier.
Dr. Webb had seen two of these explanations before. One of them was almost always wrong.
He just needed the evidence to tell him which one.
Your investigation begins now.
Ninety-four passengers evacuated on a dark October evening because a regional jet came down in the grass beside a runway it should have landed on cleanly.
Two experienced pilots insist they were pointing at the runway the entire time. The airport reported moderate winds. The previous aircraft had no problem. And the aircraft's systems — examined in the wreckage — show no fault.
Examine all five Evidence Files. The flight data, the instrument records, the weather observations, the radar analysis, and the vector reconstruction all have something to say.
The physics of what happened to Flight 417 is preserved in the data. Can you reconstruct it — and determine whether the crew could have done anything differently?
Instructions:
Play solo or with a team of up to 5 investigators. Examine the five Evidence Files together, or divide them among your team and have each investigator analyze different clues. Share what you discover, compare theories, and decide which evidence matters most.
When you've examined all the evidence, work individually or as a team to reach your final verdict—then reveal the solution to see if you cracked the case.
EVIDENCE FILES
EVIDENCE FILE 01 +
EVIDENCE FILE 01 — FLIGHT DATA RECORDER ANALYSIS
Case Reference: AAIB-2024-1022
Evidence Item: EV-01 — Flight data recorder and ground track analysis
Prepared By: Dr. Marcus Webb, Aviation Accident Investigation Bureau
Date: Wednesday — 9:00 AM
BACKGROUND
The Flight Data Recorder — FDR — is a tamper-resistant device that continuously records hundreds of aircraft parameters throughout every flight. It survived the accident intact. Parameters relevant to this investigation include aircraft heading, track, airspeed, groundspeed, altitude, control inputs, and engine performance.
Dr. Webb's analysis focused on the final four minutes of Flight 417's approach — from 1,500 feet above the runway to ground contact.
KEY DISTINCTION — HEADING VERSUS TRACK
Two parameters are critical to understanding this accident and they are not the same thing.
Heading is the direction the aircraft's nose is pointing — measured in degrees from north.
Track is the direction the aircraft is actually moving across the ground — also measured in degrees from north.
In still air heading and track are identical. When wind is present they diverge — the wind pushes the aircraft sideways while the nose continues pointing in the original direction.
The angle between heading and track is called the crab angle — because a crabbing aircraft moves somewhat like a crab, pointed one way while travelling another.
FDR FINDINGS — FINAL APPROACH
From 1,500 feet to approximately 600 feet the aircraft performed normally.
Heading: 242 degrees — consistent with Runway 24 approach heading
Track: 242 degrees — matching heading, indicating negligible crosswind effect
Airspeed: 148 knots — correct for approach configuration
Rate of descent: normal
At approximately 600 feet — recorded at 19:51:43 — a divergence appeared between heading and track.
From that moment until ground contact the parameters recorded as follows:
Heading remained consistently 240 to 243 degrees — the crew maintained the correct runway heading throughout.
Track diverged progressively to the right — reaching 257 degrees at 200 feet and 261 degrees at the point of ground contact.
The aircraft was pointing at the runway. It was travelling 19 degrees to the right of the runway.
Groundspeed during the divergence period: 138 to 142 knots — slightly lower than expected for this phase of approach.
Airspeed during the divergence period: 132 to 136 knots — below the normal approach speed of 148 knots and approaching the minimum safe approach speed for this aircraft configuration.
GROUND CONTACT DATA
Ground contact occurred at 19:52:31 — 48 seconds after the heading-track divergence began.
At ground contact:
Airspeed: 121 knots — below minimum safe approach speed
Vertical speed: -980 feet per minute — significantly higher than the normal landing rate of -200 to -400 feet per minute
Lateral displacement from runway centreline: 41 metres right
The combination of low airspeed, high sink rate, and lateral displacement left the crew no viable recovery option in the final seconds.
WRECKAGE POSITION
The aircraft came to rest with its nose pointing 238 degrees — almost exactly aligned with the runway — confirming that the crew maintained correct heading orientation throughout the accident sequence.
The wreckage trail — from first ground contact to final resting position — runs on a bearing of 259 degrees — confirming that the aircraft's actual ground track was approximately 19 to 21 degrees right of the runway heading throughout the final approach.
YOUR TASK
The flight data establishes one finding with absolute clarity:
The crew of Flight 417 maintained correct runway heading throughout the approach. The aircraft nevertheless tracked progressively to the right — reaching a lateral displacement of 41 metres at touchdown.
Research the difference between heading and track in aviation. Consider what force could cause an aircraft to travel in a different direction from the one it is pointing — and what conditions would produce a progressively increasing divergence between heading and track during the final 48 seconds of an approach.
The FDR shows the crew were pointing at the runway. It also shows they were not travelling toward it.
What was pushing them sideways — and why did their airspeed fall below safe limits at the same time?
EVIDENCE FILE 02 +
EVIDENCE FILE 02 — AIRCRAFT SYSTEMS EXAMINATION
Case Reference: AAIB-2024-1022
Evidence Item: EV-02 — Flight control and navigation systems examination
Prepared By: Dr. Sarah Chen, Aircraft Systems Inspector
Date: Wednesday — 2:00 PM
BACKGROUND
Following the flight data analysis in Evidence File 01 — which showed the aircraft tracking significantly right of its heading during the final approach — investigators needed to determine whether a fault in the aircraft's navigation or flight control systems could have caused or contributed to the observed divergence.
Dr. Chen conducted a full systems examination of the wreckage at the accident site.
NAVIGATION SYSTEMS
Flight 417 was equipped with three independent navigation systems — standard for this aircraft type.
Inertial Reference System — IRS
The IRS uses accelerometers and gyroscopes to track the aircraft's position, heading, and movement independently of external signals. All three IRS units were recovered from the wreckage and examined.
Finding: all three units showed consistent heading data throughout the approach — confirming the FDR heading record of 240 to 243 degrees. No fault codes were recorded. No discrepancy between units was detected.
GPS Navigation
The aircraft's GPS receivers were examined. Signal acquisition logs showed continuous GPS lock throughout the approach with no dropout or degradation.
Finding: GPS track data is consistent with the FDR ground track record — confirming the 19-degree divergence between heading and track was a real phenomenon, not a recording error.
Instrument Landing System — ILS
The ILS receiver captures signals from ground-based transmitters at the runway to guide aircraft onto the correct approach path. ILS deviation data is recorded on the FDR.
Finding: ILS localiser deviation — the left-right guidance signal — showed the aircraft progressively right of the approach centreline from 600 feet onward — consistent with the FDR ground track data. The ILS receiver itself showed no fault.
FLIGHT CONTROL SYSTEMS
The aircraft's flight control surfaces — rudder, ailerons, elevators, and spoilers — were examined in the wreckage.
All surfaces were found in positions consistent with the crew's recorded control inputs in the final seconds of the approach — left rudder and left bank applied as Captain Vasquez attempted to correct the drift.
Hydraulic systems:
Both hydraulic systems powering the flight controls were examined. No pre-impact fault was identified in either system.
Flight Control Computer:
The flight control computer — which processes crew inputs and translates them into surface movements — was recovered and its memory downloaded.
Finding: no fault codes recorded during the approach. All crew inputs were processed and executed correctly. The control surfaces moved as commanded.
AUTOPILOT STATUS
The autopilot was disengaged at 1,800 feet — standard practice for a manual approach. No autopilot fault was recorded before or after disengagement.
ENGINE PERFORMANCE
Both engines performed normally throughout the approach. No asymmetric thrust condition — which could cause an aircraft to yaw — was recorded.
Engine data is consistent with a normal approach power setting throughout.
DR. CHEN'S CONCLUSION
"The aircraft systems examination found no pre-existing or in-flight fault in any navigation, flight control, or propulsion system that could account for the observed heading-track divergence. Every system examined performed within its specified parameters throughout the approach.
The aircraft did what the crew told it to do. The crew pointed it at the runway and it pointed at the runway. The reason it did not travel toward the runway must be sought elsewhere."
YOUR TASK
Every aircraft system examined performed correctly. Navigation was accurate. Flight controls responded normally. Engines produced symmetric thrust. The autopilot disengaged normally.
The aircraft systems did not cause this accident.
Consider what Evidence File 01 and Evidence File 02 together establish — and what they rule out. The FDR confirmed the divergence was real. The systems examination confirmed it was not caused by any equipment fault.
If the aircraft was pointing correctly and all systems were working correctly — only one category of explanation remains.
What external force acts on an aircraft in flight that could cause it to travel in a different direction from the one it is pointing — and cause its airspeed to drop simultaneously? Research wind shear and crosswind effects on aircraft on final approach.
Evidence File 03 will examine what the airport's weather systems recorded that evening — and why the answer may not be straightforward.
EVIDENCE FILE 03 +
EVIDENCE FILE 03 — AIRPORT WEATHER OBSERVATIONS
Case Reference: AAIB-2024-1022
Evidence Item: EV-03 — Surface weather records and pilot reports
Prepared By: Dr. Marcus Webb, Aviation Accident Investigation Bureau
Date: Thursday — 9:30 AM
BACKGROUND
Evidence Files 01 and 02 eliminated aircraft systems as a cause and confirmed the heading-track divergence was real. The only remaining explanation is an external weather phenomenon. This file examines what Hartwell International Airport's weather observation systems recorded during the approach period — and whether those records are consistent with the pilots' account.
HARTWELL INTERNATIONAL — WEATHER OBSERVATION SYSTEMS
The airport operates three weather measurement systems relevant to this investigation.
ATIS — Automatic Terminal Information Service
A continuously updated broadcast giving pilots the current weather at the airport. Updated every 30 minutes or when conditions change significantly.
The ATIS broadcast current at the time of Flight 417's approach — Information Delta, issued at 19:30 — reported:
Wind: 210 degrees at 12 knots
Visibility: greater than 10 kilometres
Cloud: few at 2,400 feet
Temperature: 11 degrees Celsius
QNH: 1013 hectopascals
These are benign conditions. A 12-knot wind from 210 degrees on Runway 24 produces a crosswind component of approximately 4 knots — well within the aircraft's 25-knot crosswind limit and well within the crew's experience.
ASOS — Automated Surface Observation System
A network of sensors positioned around the airport perimeter measuring wind speed, direction, temperature, and pressure at one-minute intervals.
ASOS data for the period 19:45 to 19:55 showed consistent readings across all perimeter sensors:
Wind speed: 10 to 14 knots
Wind direction: 200 to 220 degrees
No significant variation between sensors.
Anemometer at Runway 24 threshold:
A dedicated wind sensor positioned at the runway threshold — the most relevant measurement point for landing aircraft.
Threshold anemometer reading at 19:52 — the minute of ground contact:
Wind: 205 degrees at 11 knots
THE APPARENT CONTRADICTION
Every weather measurement system at Hartwell International reported moderate, consistent, unremarkable winds during the period of Flight 417's approach.
These readings appear to directly contradict the pilots' account of being pushed sideways by an unusual wind event.
Captain Vasquez reported a force pushing the aircraft approximately 19 degrees right of heading during the final 48 seconds of the approach. At the aircraft's groundspeed of approximately 140 knots a wind component sufficient to produce that drift would need to be approximately 45 to 50 knots from the left — nearly four times what any surface sensor recorded.
The previous aircraft — a turboprop that landed on Runway 24 at 19:41 — reported no anomalies. Its FDR data showed a heading-track divergence of less than 2 degrees throughout the approach — consistent with the recorded 12-knot crosswind.
On the basis of surface observations alone the pilots' account appears inconsistent with the recorded weather.
PILOT REPORTS — ADDITIONAL ACCOUNTS
Three other flight crews operating at Hartwell International between 19:30 and 20:15 were interviewed.
The crew of a cargo aircraft that departed Runway 24 at 19:38 — thirteen minutes before the accident — reported normal wind conditions during their takeoff roll.
The crew of a turboprop that landed on Runway 24 at 19:41 — eleven minutes before the accident — reported a normal approach with no unusual wind effects.
The crew of a jet that landed on Runway 06 — the opposite end of the same runway — at 19:58 — six minutes after the accident — reported a sudden brief turbulence encounter at approximately 500 feet on their approach. They described it as "a single sharp bump — like hitting a pothole — then completely smooth again."
YOUR TASK
The surface weather observations present a direct contradiction to the flight data evidence.
The FDR shows the aircraft was pushed 19 degrees right of heading during its final approach. The surface sensors show winds of only 10 to 14 knots — insufficient to produce that effect. The previous aircraft landed without incident eleven minutes earlier.
But consider the third pilot report carefully — a brief turbulence encounter at 500 feet on the opposite runway approach six minutes after the accident.
Research what wind shear and microbursts are and how they differ from surface wind observations. Consider why a weather event could be present at one altitude and location while surface sensors — and aircraft at other times and positions — detect nothing unusual.
Is it possible for the surface weather records and the pilots' account to both be accurate — and what type of weather phenomenon would explain that apparent contradiction?
EVIDENCE FILE 04 +
EVIDENCE FILE 04 — WEATHER RADAR AND ATMOSPHERIC ANALYSIS
Case Reference: AAIB-2024-1022
Evidence Item: EV-04 — Doppler radar analysis and microburst investigation
Prepared By: Dr. Yara Mensah, Meteorological Investigation Unit
Date: Thursday — 3:00 PM
BACKGROUND
Surface weather observations in Evidence File 03 recorded moderate winds inconsistent with the flight data evidence. Surface sensors measure conditions at ground level — not at the altitudes where Flight 417 encountered its weather event. Dr. Mensah analysed all available upper-level wind and atmospheric data for the Hartwell International area between 19:45 and 20:00.
TERMINAL DOPPLER WEATHER RADAR — CRITICAL FINDINGS
The TDWR data for the period 19:48 to 19:55 revealed a phenomenon the surface sensors had not captured.
At 19:49 — three minutes before ground contact — the TDWR detected a developing microburst in the final approach corridor for Runway 24 at altitudes between 200 and 800 feet.
WHAT IS A MICROBURST
A microburst is a localised column of cold, dense air that descends rapidly from a cloud base and strikes the ground — then spreads outward in all directions like water poured onto a flat surface.
From above it appears on Doppler radar as a characteristic starburst pattern — winds diverging outward from a central point.
For an aircraft on final approach a microburst produces three simultaneous effects as the aircraft flies through it:
Effect 1 — Headwind on entry
The aircraft first encounters the outflow moving toward it — a sudden headwind that briefly increases airspeed. This initial increase can be misleading — masking the severity of what follows.
Effect 2 — Downdraft through the core
Passing through the descending core the aircraft is pushed downward — significantly increasing its sink rate beyond what the crew commanded.
Effect 3 — Tailwind and lateral outflow on exit
Emerging from the far side the aircraft encounters outflow moving away from it — a sudden tailwind that sharply reduces airspeed — and lateral outflow components that push the aircraft sideways relative to its heading.
The combination of tailwind-induced airspeed loss and lateral drift in the final phase is what makes microbursts so dangerous at low altitude.
TDWR MICROBURST DATA
The TDWR recorded the following microburst characteristics:
Core position: approximately 300 metres short of the Runway 24 threshold — directly in the approach path
Core diameter: approximately 400 metres
Peak downdraft: estimated 1,200 feet per minute
Outflow wind speed: 42 to 49 knots in all directions from the core
Development time: approximately 4 minutes from first detection to peak intensity
Dissipation: approximately 19:55 — three minutes after ground contact
The microburst developed directly in the final approach corridor between 19:49 and 19:52 — the precise window during which Flight 417 was on final approach below 800 feet.
FLIGHT 417 THROUGH THE MICROBURST
Mapping the TDWR microburst position against the FDR flight path shows Flight 417 flew directly through the microburst core during its final 48 seconds of approach.
Above 600 feet — microburst entry:
The aircraft encountered the leading headwind outflow. Airspeed briefly stable. No significant lateral effect at this stage.
600 to 400 feet — downdraft core:
The aircraft entered the descending core. Sink rate began increasing beyond commanded values. Lateral outflow from the southern side of the microburst — moving northward — began pushing the aircraft right of centreline relative to the runway heading.
400 feet to ground contact — tailwind and lateral outflow:
Emerging from the core the aircraft encountered the trailing tailwind outflow — sharply reducing airspeed from 148 knots toward 121 knots. Lateral displacement continued increasing. Sink rate reached 980 feet per minute.
WHY THE PREVIOUS AIRCRAFT WAS UNAFFECTED
The turboprop that landed at 19:41 — eleven minutes before the accident — approached and landed before the microburst developed. TDWR data shows no microburst signature in the approach corridor prior to 19:49.
The microburst developed, intensified, affected Flight 417, and dissipated — all within approximately six minutes.
The crew of the jet that landed on Runway 06 at 19:58 experienced a single sharp turbulence encounter at 500 feet — consistent with the dissipating outflow edge of the same microburst as it spread laterally across the airport.
WHY THE CREW RECEIVED NO WARNING
The TDWR alert system is designed to broadcast microburst warnings automatically when a developing event exceeds defined intensity thresholds.
Review of the TDWR alert log showed the system detected the microburst and generated an alert at 19:51:58 — fifteen seconds after Flight 417 entered the microburst at 19:51:43.
The system's detection algorithm requires the event to persist for a minimum period before generating an alert — a design feature intended to prevent false alarms from brief atmospheric fluctuations. The Flight 417 microburst developed rapidly enough to be dangerous before it was persistent enough to trigger the automatic alert.
The alert was generated. It was never broadcast to the crew. They were already inside the microburst.
YOUR TASK
The TDWR data has identified a rapidly developing microburst directly in the Runway 24 approach corridor — present for approximately six minutes, undetected by surface sensors, and invisible to the crew until they were inside it.
The microburst produced three simultaneous effects on Flight 417 — a downdraft increasing sink rate, a lateral outflow pushing the aircraft right of centreline, and a trailing tailwind sharply reducing airspeed. All three effects are consistent with the FDR data in Evidence File 01.
Research what a microburst is and why it is considered one of the most dangerous weather phenomena in aviation. Consider why surface sensors failed to detect it — and what the TDWR alert timing tells you about the limits of automated warning systems when a weather event develops faster than the detection algorithm requires.
Evidence File 05 will use vector mathematics to show precisely why Flight 417 followed the path the FDR recorded — and whether the crew had any viable recovery option once they entered the microburst.
Before reading Evidence File 05 — can you predict from the physics what the vector reconstruction will show?
EVIDENCE FILE 05 +
EVIDENCE FILE 05 — VECTOR RECONSTRUCTION AND FINAL ANALYSIS
Case Reference: AAIB-2024-1022
Evidence Item: EV-05 — Vector analysis and accident reconstruction
Prepared By: Dr. Marcus Webb, Aviation Accident Investigation Bureau
Date: Friday — 10:00 AM
BACKGROUND
Evidence File 04 identified a microburst directly in the Runway 24 approach corridor producing three simultaneous effects — downdraft, lateral outflow, and trailing tailwind. This file uses vector mathematics to demonstrate precisely why those effects produced the heading-track divergence and airspeed loss recorded by the FDR — and to confirm that the crew's account is entirely consistent with the physical evidence.
VECTORS — KEY CONCEPT
A vector is a quantity with both magnitude and direction. Velocity is a vector — it describes not just how fast something is moving but in which direction.
An aircraft in flight has two velocity vectors acting on it simultaneously:
Aircraft velocity — the speed and direction the aircraft moves through the air. This is what the pilots control. This determines the heading.
Wind velocity — the speed and direction the air mass itself is moving. The aircraft is carried within this air mass whether the crew intends it or not.
Ground track — the aircraft's actual path across the ground — is the vector sum of these two velocities combined.
In calm air the two are identical. When a strong wind acts from an unexpected direction the ground track can diverge sharply from the heading — the aircraft points one way and travels another.
PHASE 1 — BEFORE THE MICROBURST
Above 600 feet Flight 417 was outside the microburst. Wind conditions were consistent with the ATIS — approximately 12 knots from 210 degrees.
Aircraft velocity: 148 knots on heading 242 degrees
Wind velocity: 12 knots from 210 degrees — moving toward 030 degrees
The wind's crosswind component relative to the runway heading was approximately 4 knots — negligible at approach speed.
Result: Ground track approximately 242 degrees — matching heading. The aircraft was travelling where it was pointing. This is consistent with the FDR showing heading and track aligned above 600 feet.
PHASE 2 — MICROBURST ENTRY — 600 TO 400 FEET
At approximately 600 feet Flight 417 entered the microburst. The lateral outflow from the southern side of the microburst was moving northward — toward approximately 350 degrees — at approximately 35 knots at this altitude.
Aircraft velocity: 148 knots on heading 242 degrees
Lateral outflow: 35 knots toward 350 degrees — northward
Breaking into components:
Aircraft velocity components:
North: 148 × cos(242°) = −69.4 knots (southward)
East: 148 × sin(242°) = −130.7 knots (westward)
Lateral outflow components — wind toward 350 degrees:
North: 35 × cos(350°) = 35 × 0.985 = +34.5 knots (northward)
East: 35 × sin(350°) = 35 × (−0.174) = −6.1 knots (westward)
Combined ground velocity:
North: −69.4 + 34.5 = −34.9 knots (southward)
East: −130.7 + (−6.1) = −136.8 knots (westward)
Ground track bearing:
arctan(136.8 ÷ 34.9) = 75.7° west of south = 255.7 degrees
The aircraft was now tracking 255.7 degrees while pointing 242 degrees — a divergence of 13.7 degrees to the right.
This is consistent with the FDR showing ground track reaching approximately 252 degrees at 400 feet.
PHASE 3 — MICROBURST CORE AND EXIT — 400 FEET TO GROUND CONTACT
Below 400 feet two additional effects intensified simultaneously.
Downdraft:
The microburst core imposed a downdraft of approximately 1,200 feet per minute on the aircraft — adding directly to the crew-commanded descent rate. The aircraft's commanded sink rate at this phase was approximately 700 feet per minute. The microburst added 1,200 feet per minute — producing the recorded 980 feet per minute net sink rate as the aircraft partially compensated with increased thrust.
Trailing tailwind and increased lateral outflow:
Emerging from the core the lateral outflow strengthened to approximately 45 knots and the trailing tailwind component reached approximately 22 knots relative to the runway heading.
Aircraft velocity: now reduced to approximately 132 knots as tailwind reduced effective airspeed — heading still 242 degrees
Combined lateral outflow: 45 knots toward 350 degrees
Aircraft velocity components at 132 knots:
North: 132 × cos(242°) = −61.9 knots (southward)
East: 132 × sin(242°) = −116.5 knots (westward)
Lateral outflow components at 45 knots toward 350 degrees:
North: 45 × cos(350°) = 45 × 0.985 = +44.3 knots (northward)
East: 45 × sin(350°) = 45 × (−0.174) = −7.8 knots (westward)
Combined ground velocity:
North: −61.9 + 44.3 = −17.6 knots (southward)
East: −116.5 + (−7.8) = −124.3 knots (westward)
Ground track bearing:
arctan(124.3 ÷ 17.6) = 81.9° west of south = 261.9 degrees
The aircraft was now tracking 261.9 degrees while pointing 242 degrees — a divergence of nearly 20 degrees to the right.
This matches the FDR ground contact track of 261 degrees and the lateral displacement of 41 metres right of centreline to within measurement accuracy.
AIRSPEED LOSS — CONFIRMED
The tailwind component at ground contact — 22 knots relative to the runway heading — directly accounts for the observed airspeed reduction.
Before microburst entry: headwind component approximately 4 knots — adding to airspeed
At ground contact: tailwind component approximately 22 knots — subtracting from airspeed
Net airspeed change from wind shift: −26 knots
Observed airspeed at ground contact: 121 knots — a reduction of 27 knots from the approach speed of 148 knots
The vector mathematics accounts for virtually the entire observed airspeed loss.
COULD THE CREW HAVE RECOVERED?
Dr. Webb assessed recovery options at each altitude threshold.
At 600 feet — microburst entry:
Drift was less than 2 degrees. Airspeed unchanged. No alert had been issued. No reasonable basis existed for a go-around decision at this point.
At 400 feet — core exposure:
Track had diverged 13 degrees. Sink rate was increasing. A go-around was theoretically possible but carried its own risk — initiating a climb with reducing airspeed inside a microburst downdraft is itself dangerous. The crew had received no warning of what they were flying into.
At 200 feet:
Airspeed 132 knots and falling. Sink rate approaching 1,000 feet per minute. Lateral displacement 30 metres. Recovery was not viable.
YOUR TASK
You now have all five Evidence Files.
The flight data confirmed the heading-track divergence and airspeed loss. The systems examination eliminated equipment fault. The surface weather appeared to contradict the pilots — until the TDWR revealed a microburst developing directly in the approach corridor. And the vector reconstruction has shown mathematically why the aircraft followed exactly the path the FDR recorded.
Using evidence from all five files — what caused the crash of Flight 417? Was the crew responsible? Was the airport responsible? Was anyone responsible — and what does this accident tell you about the gap between what weather technology can detect and what it can warn against in time?
Consider Captain Vasquez's words from the briefing:
"Something pushed us sideways. I have never experienced anything like it in 14,000 hours."
The mathematics confirms she was right. Can you build the case that proves it?
HAVE YOU SOLVED THE CASE?
Review the evidence and decide what you think happened. If you're investigating with others, discuss your findings and agree on your final verdict before revealing the answer.
Once your team has reached a conclusion, reveal the answer.