Pilot DAR mentioned:
loss of horizontal reference if you're low flying among higher ground.
Is this a widely known phenomenon in aviation circles?
I have been looking at the Icon A5 incidents that Pilot DAR is apparently alluding to and have just checked that "horizontal reference" is not mentioned in the NTSB report into the May 2017 crash.
Loss of Horizontal Reference among rising ground (perhaps as the aircraft turned towards it) does seem a viable explanation for the excessive AoA applied before the apparent stall and loss of altitude to the ground. The aircraft was heading up a valley and then began a U-turn. As the closer valley side came into view ahead it may have created a rising apparent horizon and an illusion of pitching down.
The NTSB seem to be of the view that once in the canyon all hope was lost and the exact detail of the crash may not be important to them. Indeed the word "stall" does not appear in the report however the AoA increases to 17% and then decreases sharply with rising airspeed. I was just puzzled as to the mechanism that caused this experienced pilot to lose control in this way.
Report:-
https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA
Electronic devices report (includes flight path diagrams and FDR traces).
https://dms.ntsb.gov/pubdms/search/d...163&mkey=95127
Link to Docket (except report!?)
https://dms.ntsb.gov/pubdms/search/d...cfm?mKey=95127
Pprune thread
http://www.pprune.org/private-flying...ml#post9858555