Joetom,
I'll let the questions about the airbus takeoff configuration warnings to someone who knows the answers.
About how often this type of incidents/accidents happens: quite a bit.
Read the thread a couple of pages back. There has been at least 6 accidents with victims (LAPA, India, Northwest, Delta, Lufthansa, Spanair).
There've been at least 3 take-offs w/o flaps/slats that managed to stay in the air long enough to escape a crash. In none of them the warning worked (bad switch @DCA/pulled circuit breaker @ACE/not reported). In some cases, i.e. the flaps were noted retracted after the stall alarm and quickly commanded, in others just engines firewalled and nose down while flying on ground effect until the speed was increased.
It seems there have been voluntarily reported some 55 cases in the USA alone in the past 7.5 years of attempted clean takeoffs, almost all of them "catched" by the Takeoff Config Warning System, of course.
It seems like it happens "quite often". A couple more cases, probably not reported, have unofficially been told in this thread by a couple of pilots.
There've been also at least 6 instances of known cases "after the facts" of flights that took off with unnoticed inoperative TOWS alarms (but the configuration was just fine, so nothing happened).
All this, probably, just the tip of the iceberg.
If in the past say 25 years or so there has been at least 7 known take-offs in which the crew didn't set the configuration and the alarm didn't sound (I'm not counting LAPA where it did sound nor India Air, which it wasn't reported), I guess we could factor that it's common enough so that once every 3-4 years someone forgets to set the flaps &/or slats at exactly the same time the TOWS is not working, although it not always ends up in a crash, but could've easily if the conditions weren't favourable for a recovery.
Last edited by justme69; 1st Nov 2008 at 11:52.