I have a constant worry about accidentally deleting "Default Aircraft"...
...and as for intensionally deleting them!...

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For safety and simplification, I leave them exactly where that are...

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...no problems...

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Paul...G-BPLF...FS 2004... 8-)...!
Funny thing is....I mostly fly the Default Aircraft...for all sorts of reasons!...(details supplied upon request)...

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Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.