Narrative:

3 separate sits exist that, when combined, may be laying the ground work for a serious incident. 1) the takeoff warning horn is extremely sensitive when taking off with a 5 degree flap setting. This unfortunately is the most common setting now used (though it was not originally available on the airplane -- which may explain some of the problem.) the takeoff warning horn will sound if it senses a flap setting of less than 4 degrees, which is fairly easy since the system is very 'mechanical.' various operators use different techniques to work around the problem, and both manufacturer and the FAA ignore the situation. That is the easy way out, in reality the airplane as it currently exists is prone to nuisance trips of the takeoff warning horn system when using a 5 degree flap setting for takeoff. 2) various FAA offices take a hard line view that any aborted takeoff is due to someone having made a mistake, and enthusiastically investigate such events. This is creating an environment in which pilots are tempted to try and clear takeoff warning horns while accelerating toward V1. Unless extenuating circumstances exist the FAA should not investigate aborted takeoffs. No one does one without a good reason, and they should not be put into a certificate threatening situation for having done so. 3) several instances have occurred in which mdt ground spoiler panels remained deployed during the takeoff roll. The takeoff warning horn is connected to this system and will sound, but in at least 1 instance an airplane became airborne anyway. Now why would an mdt crew ignore a takeoff warning horn? I am tempted to use heavy sarcasm here, but will spare you. As for the spoilers themselves, there is a disagreement between some of the operators and manufacturers about the best procedures to use prior to takeoff. Manufacturer wants them deployed at the start of the takeoff roll to ensure as a 'functional check,' while some operators would prefer to let the spoiler panels remain flush until the subsequent landing (known as the 'let the sleeping dog alone' school). This whole debate on how to operate the spoilers on this airplane has degenerated into an ego/turf issue, but in any case this would not be as much of an issue if the takeoff warning horn system were reliable. The solution to this situation is fairly simple: modify the flap indication system so that the tolerance for the takeoff warning horn is increased from a range of 4-20 degrees to a range of 3-20 degrees. Or even eliminate the low end tolerance, since the airplane is flyable with a 0 degree takeoff flap setting. After all, we are not talking about an large transport. Finally, a plea from the field. The regional airlines in this country are getting to be rather large and complex. We badly need FAA oversight from inspectors familiar with airline operations. Unfortunately most of what the regionals get are inspectors with strictly a GA backgnd, who are ill equipped to deal with issues such as these. Callback conversation with reporter revealed the following: the ground spoiler problem has been solved! They have been deactivated and locked in the stowed position. The wing flaps are another problem. The takeoff flap setting used to be 15 degrees and a 5 degree tolerance was permitted for the warning horn. With the new takeoff flap setting of 5 degrees, only a 1 degree tolerance is allowed. The flight crew found that if they extended the flaps beyond 5 degrees and then retracted them to 5 degrees, the false warning horn could be mostly eliminated. However, the FAA felt that the horn was a mechanical problem and would not permit that solution to be used. One problem is that if the flaps are in motion in one direction and then reversed, the flap system would often be 'trashed.' reporter feels that the FAA is being obstructionistic about the situation.

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Original NASA ASRS Text

Title: MDT SUFFERS FROM NUMEROUS FALSE TKOF WARNING HORNS.

Narrative: 3 SEPARATE SITS EXIST THAT, WHEN COMBINED, MAY BE LAYING THE GND WORK FOR A SERIOUS INCIDENT. 1) THE TKOF WARNING HORN IS EXTREMELY SENSITIVE WHEN TAKING OFF WITH A 5 DEG FLAP SETTING. THIS UNFORTUNATELY IS THE MOST COMMON SETTING NOW USED (THOUGH IT WAS NOT ORIGINALLY AVAILABLE ON THE AIRPLANE -- WHICH MAY EXPLAIN SOME OF THE PROB.) THE TKOF WARNING HORN WILL SOUND IF IT SENSES A FLAP SETTING OF LESS THAN 4 DEGS, WHICH IS FAIRLY EASY SINCE THE SYS IS VERY 'MECHANICAL.' VARIOUS OPERATORS USE DIFFERENT TECHNIQUES TO WORK AROUND THE PROB, AND BOTH MANUFACTURER AND THE FAA IGNORE THE SIT. THAT IS THE EASY WAY OUT, IN REALITY THE AIRPLANE AS IT CURRENTLY EXISTS IS PRONE TO NUISANCE TRIPS OF THE TKOF WARNING HORN SYS WHEN USING A 5 DEG FLAP SETTING FOR TKOF. 2) VARIOUS FAA OFFICES TAKE A HARD LINE VIEW THAT ANY ABORTED TKOF IS DUE TO SOMEONE HAVING MADE A MISTAKE, AND ENTHUSIASTICALLY INVESTIGATE SUCH EVENTS. THIS IS CREATING AN ENVIRONMENT IN WHICH PLTS ARE TEMPTED TO TRY AND CLR TKOF WARNING HORNS WHILE ACCELERATING TOWARD V1. UNLESS EXTENUATING CIRCUMSTANCES EXIST THE FAA SHOULD NOT INVESTIGATE ABORTED TKOFS. NO ONE DOES ONE WITHOUT A GOOD REASON, AND THEY SHOULD NOT BE PUT INTO A CERTIFICATE THREATENING SIT FOR HAVING DONE SO. 3) SEVERAL INSTANCES HAVE OCCURRED IN WHICH MDT GND SPOILER PANELS REMAINED DEPLOYED DURING THE TKOF ROLL. THE TKOF WARNING HORN IS CONNECTED TO THIS SYS AND WILL SOUND, BUT IN AT LEAST 1 INSTANCE AN AIRPLANE BECAME AIRBORNE ANYWAY. NOW WHY WOULD AN MDT CREW IGNORE A TKOF WARNING HORN? I AM TEMPTED TO USE HVY SARCASM HERE, BUT WILL SPARE YOU. AS FOR THE SPOILERS THEMSELVES, THERE IS A DISAGREEMENT BTWN SOME OF THE OPERATORS AND MANUFACTURERS ABOUT THE BEST PROCS TO USE PRIOR TO TKOF. MANUFACTURER WANTS THEM DEPLOYED AT THE START OF THE TKOF ROLL TO ENSURE AS A 'FUNCTIONAL CHK,' WHILE SOME OPERATORS WOULD PREFER TO LET THE SPOILER PANELS REMAIN FLUSH UNTIL THE SUBSEQUENT LNDG (KNOWN AS THE 'LET THE SLEEPING DOG ALONE' SCHOOL). THIS WHOLE DEBATE ON HOW TO OPERATE THE SPOILERS ON THIS AIRPLANE HAS DEGENERATED INTO AN EGO/TURF ISSUE, BUT IN ANY CASE THIS WOULD NOT BE AS MUCH OF AN ISSUE IF THE TKOF WARNING HORN SYS WERE RELIABLE. THE SOLUTION TO THIS SIT IS FAIRLY SIMPLE: MODIFY THE FLAP INDICATION SYS SO THAT THE TOLERANCE FOR THE TKOF WARNING HORN IS INCREASED FROM A RANGE OF 4-20 DEGS TO A RANGE OF 3-20 DEGS. OR EVEN ELIMINATE THE LOW END TOLERANCE, SINCE THE AIRPLANE IS FLYABLE WITH A 0 DEG TKOF FLAP SETTING. AFTER ALL, WE ARE NOT TALKING ABOUT AN LGT. FINALLY, A PLEA FROM THE FIELD. THE REGIONAL AIRLINES IN THIS COUNTRY ARE GETTING TO BE RATHER LARGE AND COMPLEX. WE BADLY NEED FAA OVERSIGHT FROM INSPECTORS FAMILIAR WITH AIRLINE OPS. UNFORTUNATELY MOST OF WHAT THE REGIONALS GET ARE INSPECTORS WITH STRICTLY A GA BACKGND, WHO ARE ILL EQUIPPED TO DEAL WITH ISSUES SUCH AS THESE. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: THE GND SPOILER PROB HAS BEEN SOLVED! THEY HAVE BEEN DEACTIVATED AND LOCKED IN THE STOWED POS. THE WING FLAPS ARE ANOTHER PROB. THE TKOF FLAP SETTING USED TO BE 15 DEGS AND A 5 DEG TOLERANCE WAS PERMITTED FOR THE WARNING HORN. WITH THE NEW TKOF FLAP SETTING OF 5 DEGS, ONLY A 1 DEG TOLERANCE IS ALLOWED. THE FLC FOUND THAT IF THEY EXTENDED THE FLAPS BEYOND 5 DEGS AND THEN RETRACTED THEM TO 5 DEGS, THE FALSE WARNING HORN COULD BE MOSTLY ELIMINATED. HOWEVER, THE FAA FELT THAT THE HORN WAS A MECHANICAL PROB AND WOULD NOT PERMIT THAT SOLUTION TO BE USED. ONE PROB IS THAT IF THE FLAPS ARE IN MOTION IN ONE DIRECTION AND THEN REVERSED, THE FLAP SYS WOULD OFTEN BE 'TRASHED.' RPTR FEELS THAT THE FAA IS BEING OBSTRUCTIONISTIC ABOUT THE SIT.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.