The posts about heading changes and who might be making them ignore the fact that the average, GPS equipped, mobile phone or tablet running an FMS app pre-loaded with a planned hijack route can be easily followed in HDG SEL mode by a child. No need for astro, FMS input training, flight plan changes, or other silly suggestions. It's more capable than the FMS in some older types and was often used as a backup, albeit unapproved.