Originally Posted by Timbo

Delta has two types; Seniority list IP's who were hired as pilots, and have moved into the training dept. and who will someday return to flying the line full time (and they must fly line trips one out of three months while instructing). Most of them are F/O's.

Then there are 'Non-Seniority List IP's' many of whom are retired Delta pilots, the do not fly line trips, but do some observation flights in the jumpseats.

There are a few NSLI's who never were Delta pilots, but very few, and they are not put on the seniority list, and do not fly trips, just observe.