Originally Posted by
tcasdescend
Why I do wrong
I know it is a rule to use QNE at high altitude and qnh at low altitude but I not know why.
Why not standardize everything at 1013hPa?
QNE is not 1013 nor any other altimeter pressure setting, as explained to you in post #8. Using 1013 does not give altitude above mean sea level (except when the QNH just happens to be 1013) and therefore is no good for terrain clearance purposes, nor for take-off and landing, except when the QNH/QFE is
extremely high or low and cannot be set on the altimeter sub-scale, in which event the QNE procedure can be used. Many pilots and air traffic controllers do not know about the QNE procedure, nor how the value is calculated (for UK readers, it's in MATS Part 1, Appendix A
Manual of Air Traffic Services - Part 1 (caa.co.uk)).