Unfortunately for me Luk's solution didn't work.
However, I'm seeing this in the event viewer:
Faulting application name: fsx.exe, version: 10.0.62615.0, time stamp: 0x559f9a9a
Faulting module name: d3d9.dll, version: 0.0.0.0, time stamp: 0x5ba3ac24
Exception code: 0xc0000005
Fault offset: 0x001b5f16
Faulting process id: 0x4088
Faulting application start time: 0x01d55b3d7730744a
Faulting application path: C:\Program Files (x86)\Steam\steamapps\common\FSX\fsx.exe
Faulting module path: C:\Program Files (x86)\Steam\steamapps\common\FSX\d3d9.dll
Report Id: c79c2122-f377-4621-8467-7bf8f0c6190b
Faulting package full name:
Faulting package-relative application ID: