One more CRITICAL item to add to your Pre-flight Checklist - always, ALWAYS, go to the Map screen (in satellite view) and make certain that the Inspire 1 AND the RC are shown on the map as being in the actual (correct) coordinates where they are currently physically located.  

"Close" is NOT good enough.  Zoom in ALL THE WAY in satellite view mode and if the location of the Inspire 1 appears to be off by more than 15 feet, do NOT assume that the satellite map is in error.  This is particularly important if you have traveled far from your last flight location or if you are in an area where the Inspire 1 and/or the RC do not have unobstructed view of the sky and access to 7+ GPS satellites.  If the location of the Inspire on the satellite view is not correct, then you most likely do not have a good GPS lock on your "real position."  If this is the case and you take-off in P-GPS mode, you could have a crash or a fly-away situation.  

What I believe happens is this: the Inspire may get an initial inaccurate GPS position (it may only be off by, say, 15 feet; you initiate take-off and aircraft rises up to hover 4-10 feet above ground; the Inspire GPS then gets a new (correct) GPS satellite fix; then, even though the Inspire has not physically moved, the flight control software thinks that the Inspire has suddenly moved from it's initial (incorrect) GPS location to it's real current (accurate) GPS position and it WILL IMMEDIATELY TRY TO RETURN TO IT'S INITIAL INCORRECT HOME POSITION.  The result can be a sudden rapid unanticipated move of the aircraft in the direction of the incorrect initial home position resulting in a crash or injury if a building, tree or person happens to be in that direction.  

Even worse, and I don't know if or how often this might actually occur, but IF the initial GPS home point location error was huge (say, 1000 or more feet), this could result in a fly-away scenario when the GPS position suddenly updates to the correct location shortly after takeoff and the flight control software takes immediate action to return the UAV to it's initial (incorrect) home position recorded at the moment of take-off.  The same precaution and potential issue can occur with a Phantom 2 Vision+ UAV.  I own both a P2V+ and an Inspire 1 and have experienced this issue (rarely) on both aircraft.

In 25 flights with my Phantom 2 Vision+ V3.0 (latest firmware), I have seen 15-25 feet errors in initial home position twice - both times when trying to launch from my back yard where clear view of the sky is restricted by surrounding homes and my garage.  The first time I dismissed the incorrect position of my craft on the satellite view (Phantom shown 25 feet west of actual position on neighbor's home) as "map error" since I had 7 GPS satellites.  When I tried to takeoff, the Phantom started bouncing sideways on the ground in the direction of the neighbor's house.  I realized what was happening, shut down, moved my Phantom to a different spot in the yard, got an accurate GPS fix (confirmed by the view on the satellite view on Ground Station map) and took off without problem - straight up - 10 minutes later.  The second time this happened, I did not even attempt to take-off.  I just moved the Phantom to another location and waited until I had an accurate home point location shown on the satellite view map.  NOTE: these errors occurred even though I showed 7 GPS satellites.  Personally, I don't like to fly unless I have 10+ GPS satellites, but that is not always possible unless you are in a completely open area.  Currently, you cannot see the number of GPS satellites the Inspire 1 has locked onto in the Pilot App - only 5 bars.  I assume 5 bars = 7+ GPS satellites.  I hope DJI revises the Pilot App soon so we can see the actual number of satellites locked.

Based on my experiences with my P2V+, I now carefully check my indicated aircraft GPS position in satellite view mode on both my Inspire 1 and my P2V+ BEFORE taking off in either aircraft.  I do not initiate take-off unless I have an accurate GPS location indicated on the Map screeen.

In 15 flights with my Inspire, I have seen a bad GPS home point fix just one time - it was off by ~ 25 feet.  With aircraft and RC turned on, but props not turning, I picked up the Inspire, walked in a 20 foot circle, set it down and now had an accurate GPS fix (i.e., location of Inspire on satellite map view agreed within a few feet of actual position).  

Let me know your thoughts on the above and your personal experiences with inaccurate initial GPS home point fix.

Interesting. Thanks for the information.

Great thread!! I experienced exactly the same situation. prior to flight I noticed the Inspire and the RC were shown on the map as being more than 50 feet apart. I re calibrated and watched the map screen as it calibrate, you could see the inspire and RC slowly merge  together. Again great thread!

That sounds interesting. I do check my map every flight and wondered the same thing. However, I'm not convinced that the fly away issue is related to the home point at take off. My reasoning here is that were this the case the Inspire would constantly attempt to return to the active home point regardless of input from the tx. I feel you are on the right track though. I do agree that you should not launch with an erroneous home point because if for some reason you need to return to it, you may be landing in the forest or on the police station. Perhaps you are right? Dji should be screening all these posts for input so that they can improve by a process of elimination, Great thoughts keep up the safe flights and have fun.

This is realy interesting. that could be the answer of the crash I had. Took off, hovered and suddenly it towards a wall of a building (5 mtr away). Couldn't correct and crash against the wall. When I saw the flightlog I couldn't see any sideway movements of the sticks.

So this is interesting stuff!

Great post, I will definitely incorporate this into my pre-flight checklist!  Thank you!!!

Thanks for this information.. but on my tablet I don't have access to a map.
when I flew with my phone as a screen, because of the data I had access to googlemaps
but my tablet doesn't have that access.

So your check is a check I am unable to do?

Barbara Posted at 2015-11-4 02:06
Thanks for this information.. but on my tablet I don't have access to a map.
when I flew with my pho ...

Cache map data before flying.

Good point. DJI should add this to manual and startup procedure.

Gòod post, for all to remember.