A routine mission to photograph NASA from our day job almost ended in tragedy as our XbeePRO 900's lost contact & the vehicle headed for a roof.
The XbeePRO 900's sucked from day 1. The problem seems to be they only do 50mW compared to the 90mW of the original XBee PRO 2.4Ghz. They also spread the signal more omnidirectionally, making for all around weaker reception.
900Mhz normally had 10% packet loss while occasionally getting nothing while the 2.4Ghz normally got all packets & occasionally nothing. You could get better reception by rotating the 2.4Ghz wire antenna in azimuth & keeping it parallel. Rotating the 900Mhz wire antenna didn't really do anything. Finally the 900Mhz interfered more with all the other avionics.
Upgrading to the 900Mhz equivalent of an XBee PRO for $42 was too good to be true. You need to unload more money in high gain antennas & haul around a tracking mount in addition to your laptop, batteries, transmitter, & video downlink.
Best to stick with 2.4Ghz unless you're loaded with government loans or know someone at AIG.
So ignored the warning signs during test flights, insisting the 900Mhz hype was true. Sure enough, while scrutinizing video telemetry, saw the vehicle was suddenly pointing the wrong way & was over a roof. Took manual control, but the radio was gone.
We don't do RTL because of the chances of an autopilot malfunction sending it into a human or an engine spinning up on the bench. Best to let it drop if the radio dies.
Fortunately it was 1 of the few non government buildings still inhabited & with tenants who could access the roof.
It somehow crashed right side up, mostly undamaged & took 4GB of roof photos. Both main & preview cameras captured the action. If it was a pure autonomous flight, leaving us enough bandwidth to monitor the radio, this wouldn't have happened, but had to play with our $50 UART cam.