New Look.....
..and catching up with some responses...
Beagle...
Yes they were flying by Lat/Long to WGS84 but the unit had an option to use local grid info which in this case was the Irish grid....but the actual
differences were only a few feet....
ExGrunt...
A quick refresh on GPS , derived from earlier experiments using satellites ,
and culminating in the aid we now know and love.?...... a few years earlier
in 1986 the GPS coverage was really poor , the round the world flight by
Voyager only had use of GPS for about 1/3 of the record breaking flight .
They had to rely on Omega ........incidentally the same year Racal
announced the SuperTANS......
Only earlier in 1994 had the full set of satellites been completed , the last
two of the 24 having been launched in March I think , but later that
year two of them were giving problems and had to be switched to use an
alternate frequency of operation.....but for some time after they had to
constantly tweak the orbits to get them all syncronized .....
....so 1994 was still early days in terms of
developing a stable product.......
Tucumseh....
I thought it was only the use of GPS which they had been warned against , in Doppler mode the SuperTANS should have behaved much as
the TANS fitted to MK1 Chinook surely ????.....
The data extraction technique used by Racal may not have been a normal
maintenance or repair procedure , but had probably been used before in
design and development , and maybe on the assembly/test line too ........
They were carefull not to try and power up the damaged RNS252 as a
complete unit , but added an external battery to the memory card before
unplugging it . By inserting the card into a know good unit and powering
up in test mode they were sure to preserve the data , by not allowing
the unit to initialise itself .
The only clever bit as far as I can see was transcribing the 8000
characters from what was usually machine code (hexadecimal code....a
mixture of numbers 0-9 and letters A-F) into English so we could read
it ......each pair of characters translates to a real number or letter
or space,hyphen whatever......
Doing it by hand manually would take forever and it sounds like they wrote
a program to do it.....
Jayteeto
As you have used this equipment , perhaps you can confirm that the
accepted initialisation procedure came to be something like , power
up , then wait for the GPS to find satellites , then check that the position
given was accurate , if not ...give it longer to sort itself out......then
when you are confident that it is good , load the location into the
Doppler/DR before the A/C moves .........??????....
In this way any automatic initialisation which the box is programmed to do
on power up becomes irrelevant.?
..but this was the first SuperTANS in NI..we are given to believe that
there was a low level of confidence and understanding of the box at that
time......what could the crew have done , or thought they had done to
give them a safe margin passing the Mull.....???????...
Another point which keeps appearing.......they would never have turned
onto the heading to track towards waypoint 'B' at that time....as it would
entail overflying high ground , with the same arguments about
icing limitations....
..anyone who mentions that has obviously never looked at a map of the
region.....
Their only course under vfr had to be navigating at low level between the
many islands and then turning to follow the Great Glen .....
..and another thing , I can find no mention of Turnberry VOR in any
discussion or report....??.
.. this would have been their nearest VOR as they approached the
Mull.....and a DME check would have confirmed their East/West position.
...but , 34 NM West of the old airfield would have given them a safe
clearance...
..whereas 34NM DME from the VOR would have taken them into the
Mull....as the VOR is inland on a hill... .
A very basic mistake maybe , but I do not know exactly what charts they
had to work from....
rgds Robin....
Last edited by Robin Clark; 1st Mar 2010 at 09:02.