DC10 engine anti-ice
If i remember correctly (been on the Ten 20 years ago), Douglas manual stated: "Engine anti-ice must be selected ON if icing condition is encountered or anticipated".
The manual define icing condition as:
OAT(on ground)/TAT (inflight) of 6 deg or less, with:
a.visible moisture or
b.temperature and dewpoint differ by 3 deg or more