GENERAL NOTE
Printed in the “International Express”, just after the crash, as part of a big feature, a sub section entitled “Mull is Britain’s Bermuda Triangle” (but no journalist’s name given) included this little snippet: “Even the addition of sophisticated ground beacons which “speak” to instruments aboard aircraft has not removed the threat of the Kintyre Triangle”. Now, I wonder where the Express journalist got that from?
Arkroyal
You bring up points that I must address:
You wrote << the GPS and Doppler sides are separate. Poor doppler sea returns woulld have no effect on its sattelite accuracy >>
There appears to be some confusion as to the scope of the avionics upgrade – I believe that Mk 2 is on a par with 47D which means ZD576 had some changes that are significant to this debate.
The GPS and Doppler ARE combined in the upgraded HC2, in the AN/ASN-128B/C as fitted to 47Ds (as detailed below);
(BAE systems product info)
<<The AN/ASN-128B/C Doppler/GPS Navigation Set provides the advantages of a Global Positioning System (GPS) receiver and a self-contained Doppler navigation system. System installation and aircraft modifications have been minimized by embedding a Trimble one-card GPS receiver into the AN/ASN-128 Signal Data Converter (SDC) unit.
<<The AN/ASN-128B/C provides continuous velocities, navigation and guidance information. When both Doppler and GPS are available, the GPS accurately initializes and automatically updates Doppler present position. If the GPS is lost, the Doppler continues to provide accurate velocities for hover and navigation. If the Doppler is in Memory, the GPS continues to provide accurate present position; in each case navigation continues uninterrupted.>>
(Other sources)
<<The AN/ASN-128B DGNS provides a combined GPS/Doppler navigation capability through the embedding of a six channel GPS receiver into the signal data converter of the currently fielded AN/ASN-128 doppler navigation system. This system will reduce pilot workload and increase situational awareness by providing a precise navigation system. Considered a cost effective approach, the doppler with embedded GPS was recommended by a Draper Laboratory Study commisioned by PM-AEC. The 128B is the objective solution for the UH-60 & CH-47 fleet.>>
The problem of combined systems is when one is degraded (eg Doppler over water) because of how the two inputs are combined (mathematical algorithms) the net result can be worse than a single good input. This problem was well understood from the days when inertial navigation systems were complimented with Doppler radar systems – going over water was the thing for the radar return.
You wrote << IF they were that close to the high ground, and barrreling towards it relying on a piece of kit (which would have been less accurate than the on board TANS) >>
REGARDING THE ACCURACY OF THE SUPERTANS
Rather than argue technically further, I rather think this extract sums it up well:
Chinook ZD576: Select Committee Report
5 Nov 2002 : Column 661
<<… an incident that occurred on 13th July 1995, when a Chinook Mk2 helicopter was tasked to perform an over-flight of Flight Lieutenant Jonathan Tapper's memorial. The RNS 252 SuperTANS displayed an error of just 210 feet, yet the crew who were in visual contact with the ground, could see that the TANS was more than two nautical miles in error. The TANS system believed that it was some 12,000 feet away from its actual position. >>
Further, I believe that Flt Lt Tapper had warned the rest of the flight over his concerns regarding the accuracy of the TANS.
A distance measuring system is, on the other hand, very accurate – “pin point”.
PPRuNe Radar
You wrote: <<at the time of the accident, Aldergrove was not SSR equipped and therefore would not have observed any code>>
Well Belfast was – they were tracking it initially and in communication with it until 10mins before crash – I wonder what squawk code they saw? And I mean, what did they actually see – not what could have been selected/should have been selected/ etc etc..
AND further you wrote:<<… both of which would be very hard pushed to pick up a low level target in the accident area due to terrain shielding and line of sight restrictions. Otherwise the radar recordings would have been used to provide a lot more evidence of ground track and altitude in the accident enquiries.>>
– well how about this:
Circa 1st week July 1994 (reference detail lost - Author Owen Bowcott) – article titled “Radar recording ‘shows helicopter hit hillside due to navigation error’”
“Recordings of military radar tracking the RAF helicopter which crashed on the Mull of Kintyre last month show it flew straight into the hillside without altering course, writes Owen Bowcott.
“The flight path, revealed by air traffic control sources yesterday, reinforces suspicions that the accident was caused by a navigational error.
“… A controller who had seen the recordings, and requested his identity not be revealed, said: ‘The Chinook looks like it went more or less straight into the hillside. There was no distress signal. It all points toward some sort of navigational error. The pilot must have misjudged his position. He only needed to be half a mile to one side.’”
Surely, you could have replied the first time in a more positive manner (eg “try Belfast” or even better “I’ll find out for you”!) – I am only pushing for the truth, not for points.