[Pfeil]

I'm afraid that's not the way file extensions work. The extension does not determine the content of the file. In fact, it doesn't even determine the type of file it really is(In theory the header does, even though Windows uses the extension).

To make sure I'm not misinforming anyone, I tested your theory.
As I expected, recording an ntrk manually saves an ntrk file in a binary format. I.E. not a human readable plaintext file.
Saving a track at the end of a mission and renaming it to .ntrk however, doesn't even save as an ntrk extension.
.trk is automatically added to the filename you entered(I.E. test.ntrk.trk).
The resulting file is a text file with a structure similar to an FMB mission.

Edit:
I've noticed what appears to be a bug/inconsistency in the FMB: If the waypoint type is set to landing, both height and speed will be set to 0, when switching the type back to a normal waypoint, only height will be reset.
Speed will remain at 0(though will reset to the lowest speed possible for that type of aircraft if changed to anything below it, as is normal behavior).
This causes the aircraft to fall immediately after spawning(Engines running, can of course be recovered from if altitude is sufficient).

Also, if either an AI or player aircraft is spawned with only a single waypoint, set to landing, the aircraft will spawn on the ground with running engines.
As it is a landing waypoint, speed cannot be set.
Height can be set to any value and will only reset in certain cases to 12000m. However, this will not change the spawning altitude(It remains at 0).

Edit #2:
Not a true bug, but if the screenshot mode(ScreenshotType) is set to 2, a TGA and a Jpeg screenshot are saved with sequential filenames(grab0000.tga, grab0001.jpg). As these screenshots are the same image(with different compression/formatting) would it not make more sense for them to have the same name/number(I.E. grab0000.tga,grab0000.jpg)?
I'm assuming mode 2 calls functions for a tga screenshot and a jpeg screenshot in sequence, causing them to "see" the previous image, regardless of extension, and setting the number ++.
If possible, these could be integrated into a single function or made aware of extensions.