American Airlines DC9 landing incident at O'Hare

[captjns]

Originally Posted by jondc9

I read somewhere that some planes had a ground sensing mechanism on the nose strut to make sure the nose wheel was on the ground prior to thrust reverser deployment? do you know if AA had it that way?j

Yes most aircraft have a thrust reverser isolation valve which is a function of either radio altimeter sensing and/or main landing gear squat switch positioning. On some aircraft it was a function of the nose switch as to prevent thrust reverser damage on initial touchdown with a high nose attitude.