SKY (compressed archive)
From Just Solve the File Format Problem
SKY is a compressed archive program for DOS, and its associated file format. It was developed by Jean-Michel Herve and SkyTech.
SKY format seems to be essentially the same as AMG format, except for the first 3 bytes. Note that SKY is a command-line utility, not menu-driven like the main AMG software.
SKY files most likely always start with bytes
bc 40 10.