forget said:
When the MD-80 RAT Heat MEL was written up it allowed flight with no forecast icing conditions. Simple, and no problem so far. Pull the RAT Heater circuit breaker and off you go. Crucially, what wasn’t considered by the MEL writers was why the RAT might Heat on Ground. A failure of Relay R2-5 (Flight Mode) would do it – which would also disable the TOWS. So, pull the RAT Heat circuit breaker, RAT Heat problem fixed, TOWS is now inop with NO indication of failure. And I defy any line engineer, no matter how smart, to raise his hand and say “Hold on guys, RAT Heat on, I bet R2-5s failed and we can’t just pull the RAT breaker because the TOWS might also be inop”. That’s down to the MEL actions and, from what I’ve seen in this case, they ain’t up to the job.
This accident has been waiting to happen from the day the aircraft left Long Beach. Very poor TOWS/Flight/Ground logic design, and very poorly written MEL.
Purely from logic perspective - the conclusions (a) that MEL writers did not consider why RAT might heat on ground and (b) that the MEL was poorly written is not justified by your argument you present, unless the MEL actually contemplates the scenario of the RAT heat operating when air/ground logic dictates that it should NOT be operating. If the MEL merely states that flight is permitted with RAT heat inoperative (for whatever reason) in certain circumstances (no icing forecast), then the MEL did the job it was designed to do. Of course it is possible to argue that it should do more - but that's another issue.