Locating VH-MDX: Radar &‘the tale of two final fixes’

Glenn Strkalj BWRS December 2014

Revision 1, May 2015

Radar: Two Technologies Used on Each Radar Head

Drawings: Dick Barrett 2000-2002 Glenn Strkalj 2014SURAD Photo: Fighter World Aviation Museum 2014

• Primary Surveillance Radar (PSR): -‘Bouncing’ a radio signal off an aircraft

- Reliant on aircraft physical characteristics (shape, materials, aspect, geometry etc)

Drawings: Dick Barrett 2000-2002

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• Secondary Surveillance Radar (SSR): -‘Talking’ to a piece of aircraft equipment

- Not reliant on aircraft physical characteristics - A ‘conversation’ is taking place

Aircraft transponder model as reportedly fitted on VH-MDX Drawings: Dick Barrett 2000-2002

Glenn Strkalj 2014

ATC Radars Involved (3x)

• Sydney (SYD) RSR (Route Surveillance Radar) (Located at Sydney Airport)

• The Round Mountain RSR (Located west of Coffs Harbour) (Used by SYD ATC)

• RAAF Williamtown (WLM) SURAD Terminal Approach Radar (TAR) (Located at RAAF Williamtown, north of Newcastle)

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Radar Head Positions & Distance to VH-MDX

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Base Image: Melway Publishing Pty Ltd 2014Overlay Information: Glenn Strkalj 2014

Radar Mask Angle• Antenna tilt angle is NOT a hard mask

angle• Antenna tilt biases power to where it

is needed and to avoid anomalous returns from ground reflections

• Both PSR and SSR antennas have DEEP vertical coverage!

• Low-level radar coverage is normally limited by blocking terrain and earth curvature

• Low-level radar range can be affected by antenna tilt (due to power limitations)

• WLM TAR has been proven to have rather good low-level coverage out to ≈45NM

SSR Hog Trough antenna vertical propagation: (Zatkalik.J, Sengupta. D.L, Tai. C, 1975)

PSR cosecant squared antenna ideal and actual vertical propagation pattern: (The Ohio State University 2014)

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RADAR Ability: Sydney RSR• As the Sydney RSR head was located close to sea level,

terrain and earth curvature generally blocked Sydney RSR from VH-MDX from at least 8500’AMSL and below

Base Images: Radio Mobile 2014, analysis: Glenn Strkalj

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Sydney RSR located at Sydney Airport

Various terrain and possible Earth curvature obstructions

VH-MDX approximately 5NM NW of Craven waypoint at 8500’AMSL

Zoom of Various terrain and possible Earth curvature obstructions

RADAR Ability: The Round Mountain RSR

• The Round Mountain RSR perched atop a high range (5200’) could generally interrogate VH-MDX down to at least 6000’AMSL

Base Image: Radio Mobile 2014, analysis: Glenn Strkalj

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Radar propagation path clear of terrain

The Round Mountain RSR

VH-MDX approximately 5NM north-west of Craven waypoint at 6000’AMSL

RADAR Ability: Williamtown TAR

• Williamtown TAR could Interrogate VH-MDX down to at least 3500’AMSL

Base Image: Radio Mobile 2014, analysis: Glenn Strkalj

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Sydney ATC ‘Northern Mosaic’ Display

Glenn Strkalj 2014Base Image: Australian Government (DoT) 1981, Overlay information: Glenn Strkalj, 2014

The Northern Mosaic display program presented both Sydney RSR and The Round Mountain RSR radar information based on a priority system

Sydney ATC ‘Northern Mosaic’ Display

Glenn Strkalj 2014Photo: Price c.1983

SURAD Plan Position Indicator (PPI)

SURAD Controls

Williamtown SURAD TAR Display & Controls

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Photo: Glenn StrkaljAccess to control panel courtesy of The Australian Aviation Heritage Centre

Photo: Howard c.1983

Base Image: OzRunways 2014,Overlay information: Glenn Strkalj 2014

VH-MDX RADAR Fixes

- Confirmed: 2x SYD, 1x WLM- ASIB/RCC fix not confirmed by ATCO’sGlenn Strkalj 2014

VH-MDX Radar Fade

• Sydney ATC: At least 1x ATCO observed radar fade of VH-MDX (from transcripts appears to be around 0939:00UTC)

• Williamtown: When WLM ATCO checked radar display (PPI) at 0941:10UTC there were no VH-MDX paints (already faded or outside PPI range)

• A thorough check was conducted at 0941:20UTC with no VH-MDX paints observed on WLM PPI

• Final received transmission from VH-MDX was at 0939:26UTC

• WLM ATCO did not observe radar fade of VH-MDX

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Specific Sydney Radar Positions• Initial position 36NM north of

Singleton, slightly west of the Singleton-Mount Sandon Track (SSR Ident) @ 0928:28UTC (position ‘1’ in graphic)

• 320˚M/46NM from WLM @ 0934:30UTC

• Final position approximately 5NM west to north-west of Craven waypoint most likely around 0939:00UTC (position ‘2’ in graphic)

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Base Image: Australian Government (DoT) 1981

Specific Williamtown Radar Positions

• Only one confirmed, ‘complete’ (bearing & range) radar fix at 320˚M/45NM at 0936:00UTC

• A likely radar observation at 0938:30UTC of VH-MDX on the 330˚M bearing from WLM probably made by WLM ATCO but maybe SYD ATC

• The WLM ATCO did NOT observe final radar fade of VH-MDX• Procedural (non-radar) control was in-force: the ATCO had to

conduct duties away from the PPI • Monitoring of radar information was not required and was

secondary to procedural duties

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320˚M/45NM Fix: 0936:00UTC-ATCO stepped over to the PPI and observed the ident triangle and an SSR symbol, most likely a circle, in the 320˚M/45NM position-So, VH-MDX was already ‘there’ when ATCO moved to PPI (no bloom or transition from outer range observed)-A rule off was not required as the paints were so close to the PPI outer edge where the compass rose was-SSR symbols were variable in size as preset by technicians but around 1NM size would be minimum-ATCO confident within +/-2˚ & +/-1NM

-Other evidence suggests +4˚/0˚-SSR symbols were not clipped by the 48NM outer edge of PPI nor were they hanging over the 44NM MTI boundary: this means VH-MDX was between 45NM and 47NM Glenn Strkalj 2014

Image: Glenn Strkalj 2014

320˚M/45NM Fix: 0936:00UTC• Contrary to some suggestions, both the SYD and WLM

radars could interrogate VH-MDX’s transponder almost simultaneously (within fractions of a second to seconds of each other).

• The mode A code was irrelevant: all three radars could interrogate either Mode A 3000 or 4000. In fact they could interrogate and display any of the 4096 codes possible.

• Therefore both the SYD and WLM ATCO’s could observe VH-MDX SSR paints on their own radar displays in near real time

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320˚M/45NM Fix: 0936:00UTC

• SYD observed VH-MDX at 320˚M/46NM from WLM @ 0934:30UTC

• WLM ATCO did not detect VH-MDX at 0934:30UTC• WLM tower PPI was set to 48NM maximum range• WLM and SYD could both interrogate VH-MDX SSR

transponder close to simultaneously• Accordingly, just after 0934:30UTC VH-MDX was likely just

outside 48NM WLM• Why the difference (46NM vs >48NM)?: Expected read-off

tolerances• This can elude to aircraft speed and limit approach tracks into

the 320/45NM position Glenn Strkalj 2014

Base Image: Australian Government (DoT) 1981Overlay information: Glenn Strkalj 2014). Glenn Strkalj 2014

Final Position by Williamtown Radar: ASIB/RCC Position c.1981

-Included in the Sep 1981? Accident Investigation Summary Report-No base bearing/range information-WLM ATCO did not observe paint fade despite this graphic stating so!-No confirmation of originating authority-There was no radar track recording capability at Sydney or WLM -WLM ATCO does not recall being interviewed by ASIB-Propagation wise possible down to approx 3500’AMSLBoth SYD & WLM ATCO’s do not know where this fix

came from: Where did this originate from??????

Images: Australian Government (ASIB) 1981

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Final Position by Williamtown Radar:

BASI c.1983-This is the 320˚M/45NM position at 0936:00UTC- Makes sense as 320˚M/45NM was last confirmed, ‘full’ position from WLM-Note that the ASIB/RCC final radar position is not referred to in this Accident Investigation Summary Report (1983)-Also note that specific reference to ‘Williamtown’ radar for the final radar fade is removed in 1983 compared to Sep 1981 (top extract 1981, bottom 1983)

Images: Australian Government (ASIB) 1981 & 1983 Glenn Strkalj 2014

Final Radar Position Sydney ATC- SYD ATCO’s were almost continually looking at their radar display- Radar fade was confidently observed by at least 1 x ATCO- An ASIB officer was reasonably sure that SYD ATCO’s did observe the paint fade-The final position aligns with one ATCO’s assertion of an easterly track from 320˚M/45NM-Communications signal strength increase with time aligns with tracking closer to Mt Berrico- No time of final position: comms transcripts suggest 0939:00UTC-The pilot reported the coast in sight and was likely to continue tracking for the coast (east)- Final fix does not feature in ASIB/BASI folio: Why?????Images: Australian Government (DoT) 1981

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- Note incorrect initial fix time- Note over-simplified track (100˚)

Conclusions: Final Radar Positions:

• ASIB/RCC and Sydney final radar positions are separated by approximately 10NM

• Equipment radar tolerances are within hundreds of meters in range and 0.8NM for WLM, 2NM for SYD (at ranges MDX was from the radars)

• Read off errors are within a few NM • Thus, 10NM is considered well outside expected normal

radar tolerances • So, one of these final radar positions is ‘correct’ the other

not• WHICH ONE?

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Possibilities of ASIB/RCC Final Fix• A consolidated or refined 320˚M/45NM at 0936:00UTC WLM

fix (if one considers the time of 1940EST and labeling of a ‘final’ fix as incorrect )

• A prediction of where VH-MDX may have tracked to based on conglomeration of radar and witness reports

• ASIB assumption that the WLM 330˚M bearing position was the final position (ASIB/RCC final fix was 326˚M WLM) and that this position was a refined 330˚M WLM position

• Position based on radar observed over-flight by commercial or DCA aircraft (that reportedly occurred) over the estimated final position of VH-MDX

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The End

Glenn Strkalj 2014