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Cambridge GPS-NAV (and 302-) Secure Flight Recorder according IGC
Problems with a GPS-fix, or faulty Flight Logs.
Backup Battery (BuBL) in the Logger:
Cambridge developed the secure GPS Flight Recorder in 1995, and since approx. 5000 Systems in 6 models have been produced, and now flying world wide . Recently we faced increasing problems with the reliability and flight records stored of the older units. On our search we came across a problem that is a mayor source for trouble:
In all Loggers a 3Volt BuBL is installed mainly for the security system, good for about 5 years. As soon as the voltage drops below 1 Volt, the electronic seal is broken, which means the flight record will not be valid according to IGC Rules (Security: fail). This equals to opening the box. It can also be, that during a flight the navigation was working correctly, but even with a full BUBL there was no usable flight record stored.
Backup Battery (BuBG) in the GPS Module:
Cambridge uses GPS-Modules made by GARMIN. These have their own 3 Volt Backup Battery soldered onto the GPS main Board. Since these modules are mostly older than 10 years, now we see the remaining voltage on these falling below 1,3 Volt. Due to low backup power the GARMIN module becomes "dumb". The module looses its memory, and does not work reliable any more. Typical is the wrong date ("default date") and GMT time, usually captured with the satellite fix. The GPS display will show for example:
"01/01/05" before getting the next GPS fix. Day time starts new with 00:00:00,
As soon as the GPS gets a fix again, Date and time (GMT) is correct, but will soon after the Logger is switched off show the old default date again.
The reliability is not reached any more. The evolution of these GPS Modules was further developed in the last decade, and CAMBRIDGE installed 7 newer models into the systems produced. At the same time these modules were better encapsulated against electronic smog, also increasing their reliability.
This means for the service, to disassemble the logger completely, unsolder the encapsulation to reach the BuBG, and replace the battery. These are only available in the USA, TEKK has them in stock.
Recommendation:
We recommend to have them changed, or exchange the GPS engine in the early loggers against a later model, as soon as you see arising problems as described.
After this mod the Logger should do its work for the years to come.
How can I control, if the BuBL is still ok?
Requirement: A 303 or GPS Display is connected to the 302/GPS-NAV
Technology:
In the CAI Loggers 6 different GPS Modules have been used. We used mainly the fully encapsulated 12 channel GARMIN GPS25-LVC. The battery used is rechargeable (accu-type), which is done during the 302 or GPS-NAV operation. Over the years this BuBG will eventually die.
Was the 302 or GPS-NAV not used over a long period, let it run say one hour first, to give the BuBG a chance to recharge. Proceed as prescribed below. Cover the GPS Antenna with some metal piece to avoid a fix.*
Control procedure:
Switch on the 302 or GPS-NAV with the 303 / display connected.
Press the left button twice until you see Latitude, still without a Coordinate*. Now press UP one button. If you see for example UTC time11:33:12, and the clock proceeds, it is a good sign. If you see 00:00:04 or higher, it means, the module just now stated counting it just "woke up".
Now most important: One button UP into the UTC Date: If you see today's date, your BuBG is still ok. If you see for example 01/01/05 or 01/01/01 it means, the module has "forgotten" it's data, and only shows the default date from Garmin's production.
Now free the Antenna to get a fix. Repeat this procedure. The time (GMT) and date should match, delivered by the satellites. If not, send the unit for service.
For a double check repeat this procedure say one week later.