Extortion 17 Coordinates, Weights, HOGE

Incident Data: CH-47D Extortion 17 Shootdown Analysis

Note on Sources: The data on this page is fully verifiable against published sources, and may be shared freely. No classified information is used or implied.

Mathlete Memorial Challenge

Complete Using Data from Section 1-6 Below. In memory of “S.”

Using the flight telemetry, determine the precise position of the helicopter at the moment of firing.

Calculate the azimuth from the Shooter to that position and compare it to the azimuth of the Local High Point.

Calculate the angular elevation of the helicopter relative to the shooter’s horizon at the moment of firing.

Compare this to the angular elevation of the Local High Point from the same origin.

Assess whether the alignment is consistent with coincidence or a pre-planned visual trigger, consistent with an ambush from a defiladed position using an offset marker.

Answer contained in the JSON file (can be interrogated using e.g. Claude or Gemini), and the Data Walkthrough, “Making the Shot”.

Data Walkthrough: Making the Shot

The last recorded position.

At 02:39 local, the aircraft’s Blue Force Tracker (BFT) transponder recorded its final position: 34.0253720 N, 68.7825670 E. Speed: 57 knots. Altitude: 326 feet above ground level. Heading: 137 degrees magnetic — southeast, straight down the valley, directly toward the landing zone.

The BFT captures position once per minute. There would be no further recording.

Between the last transponder ping and the strike point – a distance of 352 metres – the aircraft decelerated from 57 knots to an assessed 50 knots. Using the average speed, that distance takes approximately 12.8 seconds to cover.

In that same interval, the aircraft descended from 326 feet AGL to 125 feet AGL: 61.3 metres in 12.8 seconds.

That is a descent rate of 4.79 metres per second – approximately 943 feet per minute.

The projectile – assessed as an OG-7VMZ fragmentation round fired from an RPG-7 pattern launcher – took approximately 1.3 seconds to travel from the shooter’s position to the strike point.

In 1.3 seconds, an aircraft descending at 4.79 m/s drops 6.2 metres.

In 1.3 seconds, an aircraft moving at 50 knots travels 33.6 metres.

Back-projecting from the strike point along the reciprocal bearing — 34 metres horizontally, 6.2 metres vertically — places the aircraft at the moment of firing at:

**34.02318 N, 68.784784 E, 2059m AMSL**

This is the ghost position. This is where the aircraft was when the decision was made to fire.

Lining up the shot

The geometry.

The shooter’s assessed position is 34.021228 N, 68.785188 E, at 2022 metres AMSL.

From that position, the ghost sits at:

– Azimuth: 350.26° TRUE

– Elevation: 9.53°

– Range: 220.5 metres

Three kilometres to the north-northwest of the shooter, a prominent ridgeline rises to 2478 metres AMSL at 34.0494444 N, 68.7800 E.

From the shooter’s position, that ridgeline sits at:

– Azimuth: 351.33° TRUE

– Elevation: 8.17°

– Range: 3177 metres

—

The Mathlete Memorial Challenge Solution.

For S. — cryptologist, flanker, warm heart of our little group.

	Azimuth (true), degrees	Elevation, degrees
Shooter -> Aircraft at time of shooting	350.26	9.53
Shooter -> Ridgeline	351.33	8.17
Difference	1.07	1.36

At 220 metres, one degree subtends approximately 3.8 metres.

The aircraft at the moment of firing was 1.07° in azimuth and 1.36° in elevation from the dominant terrain feature.

Assessment: This was a prepared ambush rather than random fire. However it did require time to set up. The next Walkthrough, “Alerting the Shooters” explains where that time came from.

Data Walkthrough: Alerting the Shooters

The Concealment Phase

For most of its approach, Extortion 17 was acoustically hidden from the Tangi Valley.

Flying east behind the Tangi Dara ridgeline — rising to 2300 metres AMSL — the aircraft’s rotor and engine noise was directed away from the valley floor. An observer at Do Ab, at the river confluence two kilometres inside the valley mouth, would likely have struggled to know a Chinook was operating nearby.

The Reveal

At approximately 34.0364275 N, 68.7678044 E, the aircraft cleared the Tangi Dara ridgeline and turned southeast into the Logar River Valley. Two things happened simultaneously.

First, the aircraft entered a descending heavy turn — demanding significantly more lift, and therefore more engine output. Sound level increased by an estimated 10 dB above level-flight baseline.

Second, the high-frequency engine noise previously masked by the ridgeline became audible to anyone in the upper valley.

At Do Ab — 500 metres from the turn point, at the bridge and river confluence — the estimated sound level was 95+ dB SEL: louder than a chainsaw, arriving suddenly on the valley floor.

At Gharanray — 450 metres from the turn point — the same.

This was a substantial noise spike.

The Warning Window

From the turn into the Logar Valley to the strike point is approximately 2300 metres.

At a modelled cruise speed of 30 metres per second, that distance takes approximately 77 seconds to cover.

An observer at Do Ab or Gharanray, alerted by the sound spike, had a window of 75–80 seconds to transmit a warning by radio to the shooter position.

The shooter position is assessed at 34.021228 N, 68.785188 E — within direct radio range of both potential observation points, with no significant terrain obstruction on the valley floor.

In summary, the warning window was sufficient. A single radio transmission of seconds’ duration would have been all that was required.

What Potential Observers Could Determine

With a single sound event, an observer could confirm:

An aircraft was present and approaching.
It was a multi-rotor helicopter (characteristic double-beat of tandem rotors at approximately 20 Hz).
It was travelling southeast, down the valley.

Speed could not be reliably assessed from a single point. However, an observer at Tirik — approximately 650 metres from the strike point — hearing the aircraft pass Gharanray and then pass their own position, could time the interval. From the perspective of Tirik, as the aircraft reached Gharanray, it moved out of the canyon created by the steep sides of the valley: this would lead to a change in sound as the higher pitched sounds from the engine became audible. When it passed Tirik, the Doppler effect would fix its location precisely.

The distance from Gharanray to Tirik along the flight path is approximately 1200 metres. At 30 metres per second, the transit takes approximately 40 seconds.

A practised observer could derive a speed estimate from this interval. More significantly, this technique could have been applied on previous helicopter transits through the valley — building a profile of typical coalition helicopter speeds and timings over time.

The prior SAFIRE record supports this interpretation. On 6 June 2011, fourteen RPGs were fired from five or six separate points of origin at a CH-47D in the Spin Wersek area — 2.5 kilometres south of the Extortion 17 strike point. On 21 July 2011, an MH-47G was attacked near Khan Khel, 700 metres northwest of the strike location, and directly across the river from Tirik. The valley had been actively contested for months. The acoustic profile of coalition helicopters was not unknown.

Finally, and in addition, the shooters themselves could detect the approaching helicopter from its increasing volume. However the change in sound levels would have been most marked in the last few seconds of the approach, pushing to a deafening 100 dB at the engagement point. They could not have reliably estimated its position much before the final few seconds due to the effect of terrain obstructions.

The defilade that protected them from attack by the helicopter meant they realistically needed the help of an active observer or data from prior observations to prepare the shot. And at close range, the sheer noise of the aircraft — reaching 100 dB at the engagement point — would have made ad-hoc verbal coordination of the three reportedly accurate shots all but impossible. They had to be lined up beforehand.

What the Infrared Burn Added — and Did Not Add

From T-162 seconds before impact, an AC-130 overhead illuminated the planned landing zone with an infrared spotlight described in the Colt Report as “football field size.”

This was visible to any observer equipped with Gen 0+ or Gen 1 night vision — equipment assessed as available to Taliban forces in the area, including Soviet-era 1PN33B/BN-1 military reconnaissance binoculars.

From positions forward of the strike point — Hassan Khel, Joi Zarin, Koz Timurkhel — the burn on the landing zone at 34.0182553 N, 68.7904788 E was visible.

What it did not reveal was the helicopter itself. IR-absorbing coating and a probable Infrared Suppression System on the engines made direct observation of the aircraft highly unlikely. The aircraft did not silhouette against the burn from observer positions behind the strike point.

Critically: knowledge of the landing zone location was not required to establish the ambush. Once Extortion 17 passed Do Ab, the valley geometry left only one viable route — southeast, through the choke points at Gharanray, Khan Khel, and Hassan Khel, past the strike point. A helicopter heading toward Tahir’s assessed bed-down location at Dawlat Khil had to travel that corridor regardless.

In summary, the burn confirmed that an aircraft operation was underway, the geography determined where the aircraft would be.

Assessment

The probable shooter network did not require sophisticated intelligence to engage Extortion 17 at the assessed point of origin.

The acoustic signature of the aircraft’s turn into the Logar Valley would have provided a clear, high-intensity alert to potential observers at Do Ab and Gharanray with 75–80 seconds’ warning. The valley’s geography removed navigational uncertainty entirely. The prior SAFIRE record indicates the valley’s defenders had experience of coalition helicopter profiles.

Realistically, given the mission and the load profile, once the helicopter turned into the Logar Valley, there was no way to avoid alerting the shooters and giving them sufficient time to set up the shot.

1. Spatial Coordinates & Locations

(WGS 84, Verifiable. Source: Colt Report, JCAT Report, MapCarta for building obstruction and high point)

Extortion 17 Last Transponder Ping ($T_{start}$): 34.0253720 N, 68.7825670 E
Planned Landing Zone ($T_{end}$): 34.0182550 N, 68.7904790 E
Extortion 17 Strike Point ($T_{impact}$): 34.0229590 N, 68.7850320 E (Highly Probable, JCAT)
Shooter Position (Launch Point of Origin): 34.0212280 N, 68.7851880 E (Highly Probable, JCAT) +/- 3m lateral (assessed)
Building obstruction on western edge of shooter fire zone (Extortion 17 must clear before engagement, based on Mapcarta map): 34.0216836 N, 68.7850708 E
Engagement Range: 220m (stated on map in JCAT report, basis unclear, assume approx slant range at launch).

2. Altitudes & Environment

(Sources – Terrain Altitude: MapCarta Terrain Maps; All other data: JCAT report;)

Time of Incident: 02:39:00 Local (August 6, 2011).
2011-08-06T02:39+04:30
Astronomical Data: Moon set; Polaris at Azimuth 000° / Elevation ~34°.
Temperature: 22 Deg C (JCAT report)
Wind: 5 knots, 100 degrees. (JCAT)
Visibility: 9000m, haze (JCAT)
Cloud Cover: 12,000 feet, few (JCAT)
Magnetic declination, Wardak 2011: 2.8 degrees E (NOAA, cross referenced with figures in JCAT report).
Shooter Elevation: 2022m +/- 2m (AMSL), assessed based on location in JCAT report
Extortion 17 Altitude at Last Transponder Ping (AGL): 326 feet.
Extortion 17 Altitude at strike point (AGL) (given in JCAT report): 125 feet +/-25 feet.
Terrain Altitude at Extortion 17 strike point (AMSL): 2015m (MapCarta)
Extortion 17 Altitude at strike point (AMSL): 2053m +/-8m
Extortion 17 Pressure Altitude (PA): 6605 feet (~2013m), given in JCAT report
Extortion 17 Density Altitude (DA) @ 22 degrees C: 9000 feet, calculated
Note on conversion: 100 feet = ~30.48m

3. Flight Telemetry (Reconstructed)

Extortion 17 Speed at Last Transponder Ping ($T_{start}$): 57 knots (given in JCAT report, BFT Transponder)
Extortion 17 Heading at Last Transponder Ping: 137 degrees M (Source: JCAT report, BFT Transponder). ~140 degrees TRUE (calculated, using 2011 Wardak declination)
Extortion 17 Speed at Strike Point ($T_{impact}$): 50 knots (approx., given JCAT report, as assessed by JCAT)
Extortion 17 Heading at Strike Point: ~137 degrees M (Source: JCAT Report, as assessed by JCAT). Linear deceleration between Ping and LZ (assessed, highly probable). ~140 degrees TRUE (calculated, using 2011 Wardak declination, cross referenced with bearing to Transponder ping).
Cross-Track Error: Strike point is 14.8 meters off the direct line between Ping and LZ. (Calculated based on above data)
Note on conversion: 30 metres per second = ~58.3 knots.

4. Helicopter: Boeing CH-47D
Dimensions (Source: manufacturer document)

Fuselage length: 15.5m
Fuselage height (at aft pylon): 5.8m
Fuselage height (cargo compartment): 2.0m
Fuselage width: 3.7m
Rotor diameter: 18.3m
Helicopter length (incl rotors): 30.1m

5. Weapon System (Ballistics)

Launcher (assessed, based on JCAT data): RPG-7 pattern launcher (Soviet-era, highly probable).
Projectile (assessed, based on JCAT data): OG-7VMZ (Fragmentation, Bulgaria, 2010, Assessed), highly probable; OG-7VM, probable.
Projectile Muzzle Velocity (OG-7VMZ): 152 m/s, OG-7VMZ; 145 m/s, OG-7VM. (Source: manufacturer, VMZ’s spec sheets).
Projectile Heading: 356 degrees TRUE (Based on grid references for POO and strike point, source: JCAT). 355 degrees Magnetic (figure given in JCAT report = ~358 TRUE, based on Wardak 2011 magnetic declination).
Projectile Travel Distance (horizontal): 193m (calculated from grid references in JCAT report)
Projectile Time of Flight (Calculated): ~1.29 to 1.32 seconds (to 193m range).
Projectile Gravity Drop (Calculated): ~8.5 meters at 193m range (Standard Atmosphere).
Note on conversion: In 1.3 seconds, a helicopter moving at 50 knots travels ~33 metres.

6. Sighting / Spotting / Aiming

Sighting: Iron sights, highly probable: illumination levels limit effectiveness; PGO-7, probable: illumination levels limit effectiveness; Soviet-era NSPU (1PN34) / NSPUM (1PN58), Gen 1 night vision, possible: limited availability, requires contrast, or lighting in local area.
Spotting: Commercial or Military Binoculars, highly probable, widely available; 1PN33B/BN-1, Soviet-era military reconnaissance binoculars Gen 1 night/infrared vision, probable: high quality, uses ambient light, benefits from local lighting or contrast, continuing availability (refurbished), sources in 2011 include Darra Adam Khel, PK; Commercial Gen 1 night scopes with reticle, possible: require contrast or local lighting, multiple sources incl. Dubai, UAE.
Additional illumination: From $T_{impact}$-162s until $T_{impact}$. Infrared spotlight (“burn”) at landing zone (34.0182550 N, 68.7904790 E). “Football field size.” (Colt report)
Origin: Overhead AC-130 IR spotlight (confirmed, Colt Report); Visible in Gen 0+ and Gen 1 night vision gear known to be available to Taliban.
Local High Point Location (Terrain feature behind helicopter from perspective of shooter): 34.0494444 N, 68.7800000 E
Local High Point Elevation (= max height of ridge behind helicopter from perspective of shooter): 2478m (AMSL)
Note: “Mathlete Memorial Challenge” tests alignment of helicopter at time of projectile launch with high point / ridgeline from perspective of shooter

7. Witness Statements (Corroborating)

Sequence: Three RPGs fired in rapid succession. All three shots assessed as accurate by USAF observers (Colt Report).
Hit: Second shot impacted the aircraft. Detonation observed on or near rear pylon. (Colt report)
Misses: First shot passed under the aircraft. Third shot observed going “over the top” of the falling aircraft. (Colt report)

8. Additional Flight Telemetry

(Reconstructed)

Hover Outside Ground Effect (HOGE) weight limit at DA 9000 feet (source: CH-47D Reference Manual, 7A-5-2): gross weight 48,000 lbs. With EAPS dust filters, HOGE gross weight limit: 47,000 lbs (estimated). Helicopters whose gross weight is above HOGE limit may become severely power constrained.
Extortion 17 Gross Weight: Not disclosed. Estimated: 45,000 lbs – 48,000 lbs.
Infrared suppression systems: IRSS estimates are not included in 45,000 lb gross weight estimate or 47,000 lb HOGE calculation, as no published bases exist to make this assessment.

Without an IRSS system, the helicopter would be visible to Soviet-era BN-1 binoculars out to maximum line of sight due to “Christmas tree” effect caused by hot engine gases interacting with rotor wash.

With an IRSS system, the probability of going beyond HOGE limit rises to highly probable (due to system weight, impact on torque due to reduced engine efficiency, need to apply torque to stabilise adverse aircraft weight distribution). However, acquiring helicopter in BN-1 binoculars would then be very difficult without contrast/silhouetting.
Flight plan, Nav Point 1 (Source: Colt Report, Mapcarta): 34.0324852 N, 68.7449165E E. Terrain Altitude 2080m (AMSL). Extortion 17 goes up behind Tangi Dara ridgeline rising to 2300m (Terrain, AMSL).
Flight plan, Nav Point 2 (Source: Colt Report, Mapcarta): 34.0364275 N, 68.7678044 E. Terrain Altitude 2030m (AMSL). Extortion 17 leaves Tangi Dara ridgeline, turns into Logar River Valley (~ 1 minute, 1 mile to final transponder ping).
Flight plan, Nav Point 3 (Source: JCAT Report, Mapcarta): Helicopter Landing Zone (34.0182553 N, 68.7904788 E)

9. Additional Tactical Information

(verifiable, note sources)

Location of earlier Ranger Raid to capture Qari Tahir: 34.0019440 N, 68.8205560 E. Village of Kamran Khel.
2011-08-05T23:00:00+04:30 (Source: Map in Colt Report).
Bed Down (Post Escape) Location of Target (Qari Tahir): 34.0126713 N, 68.7963787 E. Village of Dawlat Khil.
2011-08-06T01:35+04:30 (Source: Map in Colt Report)
Location of end of Ranger pursuit of Tahir: northern edge of village of Spin Wersek 34.00495708497565 N, 68.80110997962495 E.
2011-08-06T01:35+04:30 (Source: narrative in Colt Report).
FOB Shank (Main runway): 33.9219° N, 69.0781° E. Extortion 17 Take-off.
2011-08-06T02:22+04:30 (Source: Colt Report).
COP Sayed Abad (alt: Sayad Abad), approx, within 300m of civic centre. 34.0004° N, 68.7135° E (Source: Google Earth)
Prior SAFIRE attacks:
- 1. The Spin Wersek area is the location of 6th Jun 2011 attack where 14 RPGs were fired from 5-6 points of origin at a US CH-47D Chinook: evidence of coordinated anti-aircraft response. (Source: SAFIRE report maps in Colt Report). Location is ~2.5km south of Extortion 17 shootdown location.
- 2. On 21 July 2011 an MH-47G Chinook was attacked by 1+ RPGS near Khan Khel, ~700m northwest of Extortion 17 strike location (Source: SAFIRE report map in JCAT Report)

10. Infrastructure

Note: the inclusion of specific locations below is intended to show settlement or travel patterns: it does not imply their involvement or complicity. (Source: Google Earth)

Bridge, Spin Wersek, Alan Khil Village Road / Logar River (34.0028014 N, 68.8031553 E)
Bridge, Hassan Khel, Zamoch Village Road / Logar River (34.0217650 N, 68.7867150 E)
Bridge, Do Ab, Tangi-Dara Road / Logar River (34.0405010 N, 68.7693410 E)
Bridge, Guli Khel, Tangi Road / Logar River (34.0494230 N, 68.7619720 E)

River Confluence, Do Ab, Tangi River / Logar River (34.039795 N, 68.769135 E)

Road Junction, Joi Zarin, Zamoch Village Rd / Tangi Road (34.025861 N, 68.787599 E)
Road Junction, Do Ab, Tangi-Dara Road / Tangi Road (34.040502 N, 68.769601 E)
Mosque, Guli Khel (34.046784 N, 68.763435 E)

Mosque, Do Ab Khel (34.040502 N, 68.769601 E)
Mosque, Tirik (34.0252324 N, 68.7784676 E)
Mosque, Booch Kala (34.022725 N, 68.786059 E)
Mosque, Dawlat Khil (34.010297 N, 68.800782 E)
Mosque, Spin Wersek (34.003200 N, 68.801588 E)
Historic Buildings & Gardens, Gharanray (34.0354153 N, 68.7737070 E)

11. Valley Geography – Choke Points / Constraints (Source: Google Earth)

Choke Point, Do Ab (34.036850 N, 68.770362 E, 300m Diameter Ground, 300m diameter Air)
Choke Point, Gharanray (34.035199 N, 68.773762 E, 124m Diameter Ground, 200m Diameter Air)
Choke Point, Khan Khel (34.0269463 N, 68.7783680 E, Unconstrained Ground, 200m Diameter Air)
Choke Point, Hassan Khel (34.021479 N, 68.786435 E, Unconstrained Ground, 100m Diameter Air)
Choke Point, Joi Zarin (34.023339 N, 68.786601 E, Unconstrained Ground, 60m Diameter Air)
Choke Point, Tangi College (34.017354 N, 68.794234 E, 25m Diameter Ground, Unconstrained Air)
Choke point, Dawlat Khil (34.0114929 N, 68.7979903 E, 100m Diameter Ground, Unconstrained Air)
Choke Point, Spin Wersek ( 34.0039438 N, 68.8003587 E, 200m Diameter Ground, Unconstrained Air)

12. Flightpath (Planned, Modelled, Confirmed)

Name	Coords	Distance to Next (m)	Heading to Next (Deg, True)	Source
Nav 1	(34.032500, 68.744917)	2154	78.33	Colt Maps (Flightplan)
Nav 2	34.036417, 68.767806	153	54.06	Colt Maps (Flight Plan)
Turn Into Logar Valley	(34.0372277, 68.7691556)	439	120.59	Model
Gharanray	(34.0351100, 68.7734790)	260	142.8	Model
Firni	(34.0332476, 68.7751849)	362	166.98	Model
Logar 3	(34.0300720, 68.7760713)	314	159.67	Model
Kahn Khel	(34.0274226, 68.7772555)	246	121.04	Model
Tirik	(34.0262831, 68.7795398)	297	109.96	Model
Last BFT Ping	(34.0253720, 68.7825670)	352	141	Confirmed BFT (137 Magnetic Heading)
Strike Point	(34.0229590, 68.7850320)	Null	141	Assessed, JCAT
Nav 3 HLZ	(34.0182553, 68.7904788)			Colt Maps (Flightplan)

Trace (Do Ab > Gharanray > Khan Khel)
Time: 01:26-02:11 (Clip, 46s, Dari language audio).

Context: This footage simulates the Pilot’s Eye View (approx. 500ft AGL) of the Extortion 17 flight path, from the turn point into the Logar Valley through to 1km from shootdown point. The final frame shows Tirik (right of picture), the shootdown site, Spin Wersek (brightly illuminated mountain centre right, distant), Khan Khel (centre left).

Correction: The narrator identifies the road as the “Kandahar/Kabul Highway.” This is incorrect; it is the Tangi Road. The Highway is 8km East.

https://youtube.com/clip/UgkxFwtlsj_HKvmeFSDDG0vVpXFPcFW83pRM?si=RBPJw41kU8Qc8h8p.

13. Potential Observation Points

All are near a choke point and the river. Locations are indicative, rather than precise. Probability is author assessment.

Name	Coords	Elevation (m)	Probability
Guli Khel	(34.048096, 68.762380)	2048	Probable (Major Bridge)
Do Ab	(34.0415115, 68.7668388)	2025	Highly Probable (Bridge, River Confluence)
Gharanray	(34.035415, 68.773707)	2020	Possible (Constrained Chokepoint)
Khan Khel	(34.0280265, 68.779093)	2018	Possible (+ Long sight lines , – Dangerous / exposed)
Tirik	(34.0252324, 68.7784676)	2030	Possible (Long Line of Sight, if using NVGs)
Booch Kala	(34.0226723, 68.7858949)	2015m	Unlikely (+ Bridge, – Dangerous)

14. Sound Models

These are models of sound propagation based on the above flight model and assessed observer points, and using data from Schomer, Paul D. et al. “Operational Noise Data for CH-47D and AH-64 Army Helicopters”. The sound models consider terrain impact but do not take into account atmospheric effects, channeling or noise pollution (e.g. due to other helicopters operating in the area).

Chinook helicopters make sound of a double rotor beat around 20 Hz; high frequency engine noise at around 1000 Hz. These will be impacted by Doppler shift (sound rises in pitch as aircraft approaches, drops as it passes).

For comparison:
75 dB is a conversation or typical TV volume
85 dB is a loud household appliance like a blender
95 dB is a chainsaw or speakers at a music gig

Sound Build-up Model

Helicopter makes descending heavy turn into Logar Valley. After turning into valley, helicopter is modeled in level flight AGL 100m, 30 metres per second (AGL 328 feet, 58 knots) until after BFT ping when it moves into landing phase.

In this scenario, shooters can assess helicopter is approaching due to increasing loudness.

From perspective of shooters:

Helicopter Position	Helicopter Status	Distance to Shooters (metres)	Noise volume (dB), SEL (est.)	Notes
Turn into Logar Valley	Descending Heavy Turn	2300	77	Heavy turn leads to sound spike
Gharanray	Level Flight	1900	75	Level flight is quieter than heavy turn.
Firni	Level Flight	1600	77
Khan Khel	Level Flight	1000	80
Tirik	Level Flight	750	83
BFT Ping	Level Flight	500	85
Strike Point	Descending, Slowing	200	100

~2 seconds before the strike, the helicopter moves from behind a local terrain feature from perspective of shooters. This will change the apparent frequency of the helicopter noise from the shooters’ perspective as high frequency sounds from the engines previously blocked by terrain become audible.

Assessment: shooters can tell a Chinook helicopter is approaching, but may find it hard to locate it until it is right on top of them.

2. Activation Model

In this scenario, sound spike activates potential observers, who warn shooters by radio of incoming aircraft.

Helicopter makes descending heavy turn into Logar Valley, after having previously been in level flight behind Tangi Dara ridgeline. This leads to a spike in sound level (est 10 dB even without suppressing effects of ridgeline, due to increased demand for lift placed on helicopter), plus nearby potential observers at Do Ab and Gharanray will hear high frequencies from engines previously blocked by ridgeline. Potential observers at Do Ab and Gharanray will also likely experience a strong Doppler effect, creating a sharp perceptual spike in sound.

Potential Observer Position	Distance from Turn Into Logar Valley (metres)	Noise volume (dB), SEL (est.)
Do Ab	500	95+
Gharanray	450	95+
Guli Khel	1300	85
Khan Khel	1350	85
Tirik	1600	83
Booch Kala (adjacent to shoot down point)	2245	77

Assessment: Observers at the locations shown would provide 75-80 seconds warning to the shooters. With a single data point, speed is not assessable by the potential observers. Any speed or time to arrival estimates would be based on knowledge of previous helicopter transits.

3. Tracking Model

In this scenario, potential observers are able to time the helicopter between known points by sound changes. Helicopter is modeled in level flight AGL 100m, 30 metres per second.

Potential Observer	Helicopter	Trajectory	Distance (metres)	Sound (dB), SEL (est)	Sound Changes
Tirik	Gharanray	Move past rocky outcrop	1200	77	Frequency, poss. Doppler
Tirik	Tirik	Fly past	180 slant	90	Doppler

Assessment: as the distance from Gharanray to Tirik is known, an observer at Tirik could provide a speed estimate.

Gharanray is approximately 60 seconds flight from the shootdown point.

Tirik is approximately 20 seconds flight from the shootdown point.

This technique could have been used to assess helicopter speed on previous occasions, allowing the Taliban to profile coalition helicopter missions in the area.

Khan Khel might give similar results but terrain/building effects make it hard to model.

15. Infrared Observation, note on “the burn”

Using Gen 1+ night vision binoculars (or similar e.g. “night vision” consumer devices) the AC130 Infrared “burn” on the Helicopter landing zone at (34.0182553, 68.7904788) would have been visible from positions forward of the shootdown point (e.g. in Hassan Khel, Joi Zarin or Koz Timurkhel).

Due to the geometry of the valley, the only position behind the shootdown point that had line of sight to the landing zone was Khan Khel (34.0280265, 68.779093)

Gharanray (34.035415, 68.773707) might potentially have been able to see the burn, but this would depend on precise observer location and height of local vegetation.

Due to the helicopter’s infrared-absorbing surface coating and the presumed Infrared Suppression System on its engines, it is highly unlikely these potential observers could have used infrared light from the burn or the engines to directly observe the helicopter.

The helicopter would not have blocked the view of the landing zone from these locations, making direct silhouetting unlikely from these potential observation points.

It is possible the infrared burn illuminated dust in the air allowing silhouetting vs. the sky, but absent data on dust presence or the power of the burn infrared beam, this cannot be assessed: the author’s view is this is probably not a factor.

It is also worth noting that the landing zone happened to fall on a straight line between the Blue Force Transponder ping and the target, Tahir, in Dawlat Khil. Taliban forces need not have known where the landing zone was to set up the ambush: they could simply have assumed the helicopter was heading towards Tahir. Once it passed Do Ab, the only workable route to the south east of the valley was the route taken by the aircraft (it could potentially have reversed direction near Khan Khel, and returned up the valley).

Assessment: the illumination of the landing zone may have allowed observers to know there was an incoming helicopter, but it did not provide meaningful information on helicopter location, altitude or vector. Knowledge of location of the HLZ was unlikely to be a factor in setting the ambush: a helicopter coming in from the northwest heading towards the target had to pass the ambush point regardless.

Data