Software Crashes and bugs:

I use XCSoar and I am a strong proponent of it, but I have had my share of crashes or bugs. Because of that, I'm glad to have backup loggers for OLC or Contest purposes. None of the crashes have required anything more than restarting XCSoar to recover from them. The biggest tragedy is the loss of a contiguous IGC file.

- Internal GPS on the Dell Streak isn't perfect. I've had XCSoar lose position info because of this. Not XCSoar's fault obviously. Connecting to a more reliable GPS like Flarm as the primary GPS source works great. When the Internal GPS does get wonky, you may just notice that your moving map isn't moving or updating.

Cambridge L-Nav/GPS-Nav: Remarkably stable. Only a few issues that have ever required a restart in the air. Wind data in straight flight isn't as trustworthy as I would like and switching between screens will show different arrival heights. That's me not remembering what those screens show for calcs. Not a software problem.


*** Software Limitations that produce less than reliable information: (Really Human failings to account for those limitations)

Bogus Wind:
GPS based software like See You Mobile , LK8000 or XCSoar all only understand the wind if you are circling consistently, unless you've got air data hooked up to it from an internal flight computer like a 302. Super common rookie move is to climb in ridge, convergence or wave where it can't get a sense of actual winds. Then trust the glide computer as you head off into a headwind "above glide."

Murphy's Law:
Glide computers work on theory. In theory your glider should get 40:1. In theory lift and sink will balance out. In theory the winds will be consistent. Trusting all of those theories to correlate and work out will eventually put you in a position where you will either land out, or at least need to change plans, stop and thermal, do something.

No Final Glide Mode:
Some flight computers don't take winds into consideration in final glide when you are looking to cover max distance over the ground. This means that flying into a headwind, the speed director may not tell you to fly faster than best glide.


Mountains in the way:

Older pure GPS, no map/terrain systems don't know about that mountain in front of you. If things behind the mountain are disappearing, you're not getting over it and better have an option.

*** The Good:

Wind Calculations:
XCSoar with it's GPS based winds is usually within a few degrees and a knot or two of my L-Nav that has airspeed data as well. Close enough for government work if I'm circling and winds are generally consistent.

Wind Input: XCSoar will let me manually update the wind so that I can tell it that I know I'm circling in3 knots , but I'm about to leave the convergence and fly into a 10 knot headwind for 30 miles.

Safety Margins:
Arrival Heights of 1000agl can help with Murphy's Law.

Either using a high MC value like 4.0 and then flying MC0 or using the Polar Degradation feature in XCSoar, you can further buffer against counting on published glide performance.


User Errors I've seen or done:

Wrong Polar: Jumping in the club 1-26 with your PDA still configured for an ASW-20. Makes for bold moves.

Wrong Arrival Height: Thinking your arrival height is 1000agl. Not realizing it is for 0AGL or 500AGL.


The main thing is to not blindly trust or depend on a flight computer. Have a notion of what seems correct and use that in your head to validate what the flight computer says.