Thanks for the question. Unfortunately, I've gotta head out the door to go out of town. In a nutshell, the Delta MD-88 policy would work just fine. It's going to be a busy weekend for me... so it might take a couple of days to get back on this. But I'll copy/paste the MD-88 policy when I get a chance. It is exactly the same as TWA's was on the DC-9. Do you know of any other airline (besides NWA) that operates/operated DC-9's that requires/required airfoil ice protection to be on anytime engine anti-ice is on? I guess it's possible, but I've never heard of it before.