Cautionary Tale: Logger Failures, Batteries, Backups, & GPS Altitude

My experience in troubleshooting everything from cars to soaring
instruments is that a problem can usually be traced to one cause.
Having two or even three simultaneous things go wrong at once is
relatively less likely. Yet that's exactly what happened to me last
week.

On the first day at the Fairfield Region 4N contest (USA), the scorer
told me the only flights on my flash card were from 2000. I wasn't
totally shocked. I knew there was something odd about my Cambridge GPS/
NAV Model 20. For about a month, when it came time to download my
flight after landing, the list in Glide Navigator II (on a Compaq
1550) showed only that day's flight, not the three or four most recent
flights it usually did (many, maybe most of you probably know where
this is going, but I didn't). Then before the contest when I tried to
upload the waypoint file, I discovered my flash card was full (Problem
#1), and had been for several flights. Typically, GNII confirms a
successful download even when the card is full so I hadn't noticed.
Worse, those flights were no longer in the GPS/NAV--I got out my
laptop and cable and checked using SeeYou. But because of this
behavior, I cleared the flash card and--just to be sure--downloaded
that first contest day's flight twice to two different flash cards. So
when the scorer told me it wasn't there, I was puzzled.

But not panicky; I had a backup: my Garmin GPS MAP76 that's worked
flawlessly for several years. Under U.S. competition rules it's
allowable. So I downloaded that flight log and turned it in.

The next day the same thing happened. So before I switched off the
Cambridge GPS/NAV, I cabled it to my laptop and used SeeYou to
download the flight to my PC. When I went to copy it to my flash card
for scoring, the PC warned me the flight was already there. How could
this be?

The flight was already on the flash card because GNII had put it there...
but with the wrong date. When I'd let the battery on my Compaq 1550
die after an extended non-flying period, I'd neglected to reset the
date (Problem #2). So the Compaq was assigning a year 2000 date to
each file. That's when I discovered that my first day's flight log was
there, too. The scorer (or maybe WinScore?) had checked only the file
date, not the file name.

That's also when it finally occurred to me that the reason my
Cambridge GPS/NAV wasn't retaining prior flights was because its
backup battery had also died (Problem #3). This is the little coin
cell that keeps the memory alive when the logger isn't connected to a
power supply. This was also consistent with GNII not asking me if I
wanted to use the GPS/NAV waypoints every time I launched it: there
were never any waypoints in the GPS/NAV to load. Like my flight logs,
they vanished every time I switched off the power to the GPS/NAV.

I replaced the coin cell that night, reset the date/clock in the
Compaq 1550, and everything worked flawlessly after that.

There were only two glitches. First, my Garmin flight log on the first
day showed me popping out the top of the start cylinder about a minute
and a half before I flew out the side of it. That's because the GPS
altitude was about 150' higher than pressure altitude at that time. I
debated submitting a protest to get the scorer to use my Cambridge
flight log--after all, I'd turned it in the previous day even though
the scorer hadn't realized it--but decided it wasn't worth the fuss.
I'd actually cruised in weak left for most of that 90 seconds towards
the first turn so the impact on my speed was negligible.

The second glitch was that my Cambridge GPS/NAV is no longer "secure."
When the battery died, so did the electronic security. I'll have to
send it back to CAI to get it reset someday. Per the manual, you can
avoid this if you power up the GPS/NAV before you replace the coin
cell. It was too late in my case because the battery had already
failed.

It could have been worse. The GPS altitude could have been off a lot
more, resulting in a dreaded
"no valid start" penalty. Or I could have lost one or more days' logs
altogether, for example if I'd switched off the logger to take it to
the scorer for downloading--as many pilots do--without the Garmin
backup. In the future, I'll replace the Cambridge backup battery at
the first sign of trouble (e.g., when it no longer shows multiple
flight logs to choose from during a download). Or maybe every year or
two: coin cells are cheap. By the way, I couldn't find the appropriate
BR2325 cell at the local Wal-Mart so I installed a CR2025 in its
place. I'm told the BR and CR prefixes are relatively insignificant. I
believe any 3 volt cell that fits will work, at least for a while. The
"23" part of the cell number refers to its diameter in mm, so anything
23 or less slides right in. And the "25" refers to its height (2.5mm)
so anything that height or less will probably work. Thicker might
work, too (e.g., a 2032, another common size), although I didn't want
to overflex the little spring clip that holds the battery down. Of
course, using a smaller battery, as I am now, means it won't last as
long. But in a contest, all you care about is getting to the last day
with no problems, right?

I know there's another backup battery in my Cambridge LNAV that
probably needs replacing (it keeps the memory alive that stores
configuration data). And another one in my Dittel radio (it keeps the
memory alive for stored radio frequencies). And another one in the
instrument-panel-mounted annunciator for my ELT (it operates the LED
that flashes if the ELT is triggered). And who knows how many more?
Sometimes I get wistful for the days when the only electronic thing in
the glider was my Bayside BEI-990 radio that operated nearly all
season on one set of batteries.

Chip Bearden
ASW 24 "JB"
USA

Is there a reason why cambridge (as well as some other flight
recorders) do not use non volatile memory instead of a backup battery
which may die in the wrong time or pop out in a crash resulting in a
loss of the most critical clue of what happened??

Ramy

On Oct 15, 12:09 pm, Chip Bearden wrote:
My experience in troubleshooting everything from cars to soaring
instruments is that a problem can usually be traced to one cause.
Having two or even three simultaneous things go wrong at once is
relatively less likely. Yet that's exactly what happened to me last
week.

On the first day at the Fairfield Region 4N contest (USA), the scorer
told me the only flights on my flash card were from 2000. I wasn't
totally shocked. I knew there was something odd about my Cambridge GPS/
NAV Model 20. For about a month, when it came time to download my
flight after landing, the list in Glide Navigator II (on a Compaq
1550) showed only that day's flight, not the three or four most recent
flights it usually did (many, maybe most of you probably know where
this is going, but I didn't). Then before the contest when I tried to
upload the waypoint file, I discovered my flash card was full (Problem
#1), and had been for several flights. Typically, GNII confirms a
successful download even when the card is full so I hadn't noticed.
Worse, those flights were no longer in the GPS/NAV--I got out my
laptop and cable and checked using SeeYou. But because of this
behavior, I cleared the flash card and--just to be sure--downloaded
that first contest day's flight twice to two different flash cards. So
when the scorer told me it wasn't there, I was puzzled.

But not panicky; I had a backup: my Garmin GPS MAP76 that's worked
flawlessly for several years. Under U.S. competition rules it's
allowable. So I downloaded that flight log and turned it in.

The next day the same thing happened. So before I switched off the
Cambridge GPS/NAV, I cabled it to my laptop and used SeeYou to
download the flight to my PC. When I went to copy it to my flash card
for scoring, the PC warned me the flight was already there. How could
this be?

The flight was already on the flash card because GNII had put it there...
but with the wrong date. When I'd let the battery on my Compaq 1550
die after an extended non-flying period, I'd neglected to reset the
date (Problem #2). So the Compaq was assigning a year 2000 date to
each file. That's when I discovered that my first day's flight log was
there, too. The scorer (or maybe WinScore?) had checked only the file
date, not the file name.

That's also when it finally occurred to me that the reason my
Cambridge GPS/NAV wasn't retaining prior flights was because its
backup battery had also died (Problem #3). This is the little coin
cell that keeps the memory alive when the logger isn't connected to a
power supply. This was also consistent with GNII not asking me if I
wanted to use the GPS/NAV waypoints every time I launched it: there
were never any waypoints in the GPS/NAV to load. Like my flight logs,
they vanished every time I switched off the power to the GPS/NAV.

I replaced the coin cell that night, reset the date/clock in the
Compaq 1550, and everything worked flawlessly after that.

There were only two glitches. First, my Garmin flight log on the first
day showed me popping out the top of the start cylinder about a minute
and a half before I flew out the side of it. That's because the GPS
altitude was about 150' higher than pressure altitude at that time. I
debated submitting a protest to get the scorer to use my Cambridge
flight log--after all, I'd turned it in the previous day even though
the scorer hadn't realized it--but decided it wasn't worth the fuss.
I'd actually cruised in weak left for most of that 90 seconds towards
the first turn so the impact on my speed was negligible.

The second glitch was that my Cambridge GPS/NAV is no longer "secure."
When the battery died, so did the electronic security. I'll have to
send it back to CAI to get it reset someday. Per the manual, you can
avoid this if you power up the GPS/NAV before you replace the coin
cell. It was too late in my case because the battery had already
failed.

It could have been worse. The GPS altitude could have been off a lot
more, resulting in a dreaded
"no valid start" penalty. Or I could have lost one or more days' logs
altogether, for example if I'd switched off the logger to take it to
the scorer for downloading--as many pilots do--without the Garmin
backup. In the future, I'll replace the Cambridge backup battery at
the first sign of trouble (e.g., when it no longer shows multiple
flight logs to choose from during a download). Or maybe every year or
two: coin cells are cheap. By the way, I couldn't find the appropriate
BR2325 cell at the local Wal-Mart so I installed a CR2025 in its
place. I'm told the BR and CR prefixes are relatively insignificant. I
believe any 3 volt cell that fits will work, at least for a while. The
"23" part of the cell number refers to its diameter in mm, so anything
23 or less slides right in. And the "25" refers to its height (2.5mm)
so anything that height or less will probably work. Thicker might
work, too (e.g., a 2032, another common size), although I didn't want
to overflex the little spring clip that holds the battery down. Of
course, using a smaller battery, as I am now, means it won't last as
long. But in a contest, all you care about is getting to the last day
with no problems, right?

I know there's another backup battery in my Cambridge LNAV that
probably needs replacing (it keeps the memory alive that stores
configuration data). And another one in my Dittel radio (it keeps the
memory alive for stored radio frequencies). And another one in the
instrument-panel-mounted annunciator for my ELT (it operates the LED
that flashes if the ELT is triggered). And who knows how many more?
Sometimes I get wistful for the days when the only electronic thing in
the glider was my Bayside BEI-990 radio that operated nearly all
season on one set of batteries.

Chip Bearden
ASW 24 "JB"
USA

On Oct 15, 1:19 pm, Ramy wrote:
Is there a reason why cambridge (as well as some other flight
recorders) do not use non volatile memory instead of a backup battery
which may die in the wrong time or pop out in a crash resulting in a
loss of the most critical clue of what happened??

Cambridge does, in the 302.

I suspect the cost of re-engineering the model 20 with more modern
innards was not cost effective considering the small market.

-Tom