Ops question virgin atlantic
 

looking up the virgin FCOM came across a topic which seems not very clear for me, maybe you could enlighten this for me ...

Company policy for reduced thrust is either TO with assumed temperature, TO2 or TO2 with ass. temperature, they don´t use TO1 at all.
Quote FCOM SP 18.12 (reffering to TODC):
"The default DERATE 0 (OPT/ASS) will generally produce TO2 with an assumed temperature unless the aircraft is very heavy, the airfield elevation is very high and/or OAT are very high. TO1 is not used"

Why don´t they use TO1? under which circumstances is TO1 then used ?