Comment by positron26

It is a very practical amount of fait.

There are two fire detection loops for each engine.[1] Even if both fails (because they get shredded as you say it) the system will report an engine fire if the two loops fail within 5s of each other. (Or FIRE DET (1,2,3,or APU) FAIL, if they got shredded with more than 5s in between without any fire indications in between.)

The detection logic is implemented directly below the cockpit. So that unlikely to have shredded at the same time. But even if the detection logic would have died that would also result in a fire alarm. (as we learned from the March 31, 2002 Charlotte incident.)[2]

In other words it is a very reliable system.

1: page 393 https://randomflightdatabase.fr/Documents/Manuel%20Aviation/...

2: https://www.fss.aero/accident-reports/dvdfiles/US/2002-03-31...

I don't know what the MD-11 would have had, again I didn't work on it. But the systems used for other aircraft would have reported an alarm based on what I saw in the video, at least they were designed to do that. The LRU receiving the sensor inputs wouldn't typically be in the wing and would be able to continue reporting the alarm condition even if the sensors fail. In fact, the lack of current from the sensor (for the systems I worked on) would have been enough to trigger the alarm if the sensor were completely eliminated.