The relevant SO rules for hot drop
Planetary Conditions
Any planetary condition modifiers (such as weather; see the Weather portion of the Expanded Movement Costs and Planetary Conditions tables, p. 36, TO) that apply to Piloting Skill Rolls are applied to the Piloting Skill Roll above. If a unit cannot be displaced (for example, all the adjacent hexes are prohibited terrain), the unit is destroyed.
Failed Landing Damage
A unit that fails its landing roll takes damage as though it had fallen a number of levels equal to the number of points by which the roll failed (see Falling, p. 68, TW, for ’Mechs or Unit Displacement, p. 151, TW, for non-’Mech units). For example, if a ’Mech with a modified Piloting Skill target number of 6 or higher rolled a 3, the unit would suffer damage as from a fall of 3 levels. A Piloting Skill Roll for landing that fails by more than 7 means the unit is automatically destroyed.
Regardless of whether a unit violates Stacking rules for entering a hex, a failed landing roll automatically is treated as an accidental fall from above (see p. 152, TW).