Nothing based on RACAL can be considered factual reconstruction. RACAL tell you so. So most of what follows is theory.
The crew ditched their Waypoint because they had visually identified it at around 2 miles. (Holbrook) They were then expected to make a gentle left turn and follow the coast. They didn't. They took up a track of 035ish.
When the crew did the manual Waypoint Change the TANS was swiched on.
It must have been or they would have been looking at a blank screen when they pressed the ENT button to accept the new Waypoint.
It is unlikely that the crew were dealing with a major emergency at this point because pressing TANS buttons would then become a low priority.
Therefore any Major Emergency and Switch Off came after Waypoint change.
It must have come very soon afterwards.
No TANS computers produce Navigation Data. They process other equipment.
When the TANS computer is switched off these other equipments continue to work.
The GM compass still sends data to all the other instruments.
The Doppler is still working and can be accessed through an analogue display in the cockpit.
The Trimble GPS and the Air Data Computer are still working. You can't access the Data with the TANS swiched off, but if you could get test equipment to the appropriate avionics rack you could still extract Data.
It is therefore perfectly feasible to supply the battery powered storage unit with all Data after TANS switch off.
The only answer required from RACAL is, was that particular aircraft wired that way.
The RACAL analysis gives GPS time of final powerdown as 1659.38
It gives GMT at shutdown as 1659.10
GPS time is precise. GMT time starts from a time entered by the crew. It is as accurate as the crews inital entry.
The RACAL report states:
"The difference of (26?) seconds between GMT and UTC is not significant since initial setting is based on keyboard entry by the aircrew."
If the TANS power switch had remained in the On position that is the only explanation. But:
I, and all the crew members I knew, started the day with a timecheck.
When entering data on a precise Navaid such as TANS, I would use an IN chart or similar to input position. I was almost as careful with time.
A 26 second entry error is a bit gash but possible. It is a pity it was not entered 26 secs late, rather than early because then it would have to be Aircrew Error.
One way of stopping the GMT clock is to switch the TANS off.
So did the crew Switch Off the TANS at 26 secs to impact or:
Did they set the time wrong by 26secs and in spite of the design safeguards in the switch, it was knocked off at impact.
From personal experience I favour the former.
It is a pity that RACAL never even mentioned the Power On / Off switch in their report.
My last rant on this subject.
Last edited by dalek; 26th Jun 2011 at 11:48.