Boeing, allegedly, told everybody after Detroit's Northwest accident that the TOWS couldn't be trusted 100% and they should be very frequently tested, specially shortly before each take off.
Unfortunately, such recommendation was never made mandatory by regulatory bodies anywhere in the world.
And worse yet, it seems Spanair was never told about it (or they weren't smart enough to find out, one of the two or a bit of both).
I guess Boeing figured on their own analysis that that was the best and most effective course of action (incidently, also the cheapest).
I concur that, with frequent tests before each take off, the likehood of an unnoticed TOWS failure at the same time as an unnoticed misconfiguration is very unlikely and reasonably safe for such an old airplane. Not "fool proof", but we've seen even worse designs being used for everyday critical operations in all industries.
At least it adds another layer to the cheese. Now 3 things would have to fail:
-The pilots missing a configuration error.
-The TOWS failing around that same time and not having been noticed on daily tests.
-The pilots missing the pre-takeoff TOWS test revealing the TOWS have become inop or the TOWS failing exactly in the few minutes (instead of up to 24h) between the check and the takeoff.
The chances of all three holes aligning are no longer that great as in the other case, where only two holes needed alignment.
Not perfect, but a pretty good, cheap and easy "patch" for the time being, until a better solution is found, if deemed necessary. At least, it would've (should've) worked on the only two known cases since Detroit: Spanair and Map. But in neither of those cases the crew performed a TOWS check right before takeoff. It wasn't even required in their SOPs.
Last edited by justme69; 22nd Oct 2008 at 17:49.