Dr Margaret Ann Rous, 37, and her husband David, 28, who was flying, were killed when their Piper Cherokee struck Beinn nan Lus, near Loch Etive.
The couple, who lived in Newport-on-Tay in Fife, were heading from Dundee for Tiree to visit family on 4 April.
Investigators said their plane hit the hill in a "steep nose-down attitude".
The Air Accidents Investigation Branch (AAIB) said no "specific" cause for the accident could be identified.
However, recorded data and analysis of the impact suggested the accident followed a loss of control of the aircraft possibly in cloudy weather conditions.
Several other pilots had chosen not to fly west from Dundee because of forecasted weather, the AAIB said.
Dr Rous contacted a relative on Tiree to ask about the weather there and was told it was "misty" and was also sent a picture of the conditions.
The AAIB report added that Mr Rous had checked the weather forecast before their flight and had expected it to improve.
Investigators said the plane was cruising at 6,500ft when it entered a gentle right turn, the rate of which increased along with a high rate of descent and speed.
They said it was possible Mr Rous experienced "some form of spatial disorientation" before the crash, which happened at about 10:30.
Investigators said Mr Rous had previously demonstrated a responsible approach to poor weather.
On a previous trip to Tiree, he opted to wait for bad weather to improve before attempting to fly from the island while Dr Rous took a commercial flight home.
A couple died after their light plane went into a steep descent and crashed nose-down into a hillside, air accident investigators have said.