Spent 37 years in aviation maintenance....in contrast to autos it’s a different animal all together.....obviously.
The tolerances are way tighter in many places.
e.g. one engine I worked on had assemblies that one side was designed to spin, the other side was static but the two needed to seal so there was no oil leakage. The flatness required to accomplish the “mechanical seal” between the two had to be in the millionths of an inch range.
To accomplish that the parts would require a process called “lapping” which is basically making the part flat.
To verify flatness the process was to measure using an optical flat that shows light bands.
Anyway, yeah things are a lot tighter in aviation.
I won’t bore you any further with light bands thing but if your at all interested this explains it.
https://www.kemet.co.uk/blog/lapping/how-to-measure-flatness-technical-article
Yea, the injector assemblies where I worked used light bands. There were machined out to 7 decimals places of an inch. Then each were measured and then classed within 49 ranges. The injector plungers were then matched with the barrels in the same class. Very tight tolerances.
“To verify flatness the process was to measure using an optical flat that shows light bands.”
I understand that. I made a couple of telescope mirrors which are in these cases parabolas but are extremely close to being spherical. A simple “knife edge” test is used to measure the curve to millionths of an inch.
Rubbing two disks of glass together with abrasive between them produces two spherical surfaces. The concave one becomes the telescope mirror.