First flight a couple of days ago. Spark with controller and iPhone in airplane mode with cable. all updates done,  no warnings, good gps, homepoint set, had done a compass calibration the day before.

Took off to about 12' and after a few seconds motors sound like they were cutting out rapidly (sounded like rapid reving up and down, like a car engine hitting the rev limiter) and came straight down, luckily on grass but flipping over.  only warning on DJI app is "aircraft tilting" or similar. battery didn't pop off which tells me it s not a battery lock issue.  

turned off the battery and controller, restarted, took off and did two uneventful 12' test flights  but this is not confidence inspiring since I will mostly be using the spark from a boat and over water...here is the loq... I don't see any red flags in there... thanks for any suggestion

http://www.phantomhelp.com/logviewer/O9B9L2JUJK5YKS3L5HSD/

"aircraft tilting" Isn't it an IMU calibration issue?

Calibrate the IMU and the compass, then check all the drone settings in the Go App then try again (over land).

Then you should be good to go

Rich

If weird sound was heard during flight, there might be possible motor defect.  Suggest you return for service first, as next flight probably won’t this lucky again.  DJI is hard to deal with and claim if there is fly away and lost the Spark.  

Sorry to hear about that.
We'd love to help you analyze the data and try to figure out what caused the accident.
Here are the instructions:
1. Download the Assistant 2 from DJI official Spark website page, install it.
2. Connect the drone to your PC, run Assistant 2, then click "black box", you can get the file.
3. Then click "Upload Data--Confirm", choose the log which showing the accident, and export it.
Please upload both files to Dropbox and post the link here, thanks.