justme69,
Many thanks for your many enlightening posts!
I agree with you 100% in your reasoning regarding the (possible) failure of relay R2-5 being a factor in this regrettable accident.
I also is convinced that relay R2-212 was working.
I flew the DC-9/MD80 series aircraft for many years - although it is 16 years since I flew the types, my memory is still more or less intact - I think!
So, therefore this comment/clarification:
You wrote in post #1937:
"It's the one ultimately feeding data flight recorder 31-31, which I'm guessing is the one recording the change of air/ground logic state (therefore, R2-212 was getting the 115VAC, sensed the oleo switch and changed the state of 31-31, so it was also working."
It appears to me that you think(?) that the DFDR starts operating when an airborne condition is sensed by the L oleo switch (and relay R2-212).
This is not so.
The only thing that happens to the DFDR is the reception of a signal indicating an airborne condition.
The DFDR starts operating when the parking brake is released and continues to operate until parking brake is set again - in order to have data whenever the aircraft is moving on the ground and in the air.
At least it was so on the DC-9.
On the MD80 I am a bit uncertain - I think that it started to operate when fuel was selected to on in the start sequence of the first engine - somebody correct me!
The CVR (23-71) is operative as long as there is electrical power on the aircraft.
The CVR gets a signal when airborne via R oleo switch and relay R2-08.
BRGDS
grebllaw123d