I joined this thread a long time ago and was shot down severely by a former MD-80 pilot when I suggested that the crew had just 9 seconds to recover the situation from the time the stall warning sounded to its impact with the ground. The interim accident report reveals that the crew misinterpreted the stall warning horn for a fire alarm and wasted valuable seconds trying to switch it off...I stand by my original suggestion that the aircraft was at least 25kts slow when the aircraft reached the
calculated Vr and V2 speeds because the flaps slats were not deployed for take-off and that the clean wing speeds would have been much higher.
However that is not the purpose behind me coming back in here; I need to talk to an Avionics guy specifically someone who has access to the wiring diagrams and or is familiar with the MD-82. I am a retired Avionics engineer and have read the interim accident report several time over, particularly in regard to the operation of the R2-5 relay and its failure history as reported by Boeing in the report. The accident report has been removed from the formento website but I can email a copy if anyone wishes to read it.
This is the point I wish to discuss; On page 39 of the report there is a photograph of the relay panel and specifically R2-5, showing its condition after the crash and I regret that what I see there is one seriously bu**ered up relay, some extremely dodgy wiring and some very dubious working practices.
The wiring bears so little resemblance to the wiring diagram I am forced to the conclusion that someone knew that R2-5 on the crash aircraft was suspect long before the crash.
The report also shows graphs taken from the QAR that indicate that the quote 'weight on wheels switch' unquote was working correctly, BUT, the switched ground from the nose wheel is in fact routed through 2 such switches on the nose wheel before being wired to the X2 terminal on the R2-5 relay. I am not familiar with the MD-80 series but my experience is that these switches on other aircraft are invariably in highly exposed areas and subject to all the muck and filth of dirty, sandy, wet runways whilst the relays themselves are in a far more benign environment and that hence the switches rather than the relays are more likely to fail, normally to some indeterminate state, neither one thing or the other.
The aircraft fleet on which I spent almost half my working life on relied heavily on the Leach 9274 series relays and I cannot remember a single instance where one has failed in a 'Weight on Wheels' scenario; however I have had to replace several associated squat switches...
Here is a link to the Leach 9274 series relay manufactures drawing; pages 4and 5 show the pinouts. Compare this with the wiring diagram shown at forgets reply 2634 and the picture on p39 of the accident report...
I'd be happy to discuss this with any avionics people out there.
pp