Narrative:

I have a thought or two that may help to prevent future problems on the DC9/MD80 series aircraft's horizontal stabilizer jackscrews. At the facility where I am a contractor a&P mechanic, a 'C' check was being performed on an MD83. We replaced a horizontal stabilizer jackscrew assembly and performed a rig of position indication system. Not long after this, the airliner accident occurred off of the california coast. There are 3 sets of circuit breakers protecting the horizontal stabilizer primary/alternate drive motors and an override switch, guarded on the l-hand aft area of pedestal in cockpit. When the crew of airliner was at FL320 the secondary drive motor was receiving its commands from the autoplt, and was in charge. There have been some DC9/MD80 series aircraft that have been modified to have heated drive motors. I have been involved with the jackscrew airworthiness directive for inspection and, although this will enhance safety a bit, the real cause of the problem seems to be side-stepped. Electronic anomaly, not mechanical failure was, I suspect, the true cause of the recent tragedy. Modifying all primary/alternate drive motors with heating element, together with replacement of all circuit breakers protecting this system, and a test of the primary motor's internal fuse protection on a recurring basis along with the present inspection/checks on the jackscrew assembly on the DC9/MD80 aircraft. A recurring detailed inspection of the switches located in the r-hand side of the forward side of the forward cargo pit. These switches are for horizontal stabilizer position indicator and autoplt pitch servo. Any wear of stops, worn switches in this area can evolve into a catastrophe if unchked or unattended to.

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Original NASA ASRS Text

Title: A TECHNICIAN WHO REPLACED AN MD83 STABILIZER TRIM JACKSCREW ASSEMBLY OFFERS SEVERAL SAFETY SUGGESTIONS PERTAINING TO STABILIZER TRIM COMPONENTS.

Narrative: I HAVE A THOUGHT OR TWO THAT MAY HELP TO PREVENT FUTURE PROBS ON THE DC9/MD80 SERIES ACFT'S HORIZ STABILIZER JACKSCREWS. AT THE FACILITY WHERE I AM A CONTRACTOR A&P MECH, A 'C' CHK WAS BEING PERFORMED ON AN MD83. WE REPLACED A HORIZ STABILIZER JACKSCREW ASSEMBLY AND PERFORMED A RIG OF POS INDICATION SYS. NOT LONG AFTER THIS, THE AIRLINER ACCIDENT OCCURRED OFF OF THE CALIFORNIA COAST. THERE ARE 3 SETS OF CIRCUIT BREAKERS PROTECTING THE HORIZ STABILIZER PRIMARY/ALTERNATE DRIVE MOTORS AND AN OVERRIDE SWITCH, GUARDED ON THE L-HAND AFT AREA OF PEDESTAL IN COCKPIT. WHEN THE CREW OF AIRLINER WAS AT FL320 THE SECONDARY DRIVE MOTOR WAS RECEIVING ITS COMMANDS FROM THE AUTOPLT, AND WAS IN CHARGE. THERE HAVE BEEN SOME DC9/MD80 SERIES ACFT THAT HAVE BEEN MODIFIED TO HAVE HEATED DRIVE MOTORS. I HAVE BEEN INVOLVED WITH THE JACKSCREW AIRWORTHINESS DIRECTIVE FOR INSPECTION AND, ALTHOUGH THIS WILL ENHANCE SAFETY A BIT, THE REAL CAUSE OF THE PROB SEEMS TO BE SIDE-STEPPED. ELECTRONIC ANOMALY, NOT MECHANICAL FAILURE WAS, I SUSPECT, THE TRUE CAUSE OF THE RECENT TRAGEDY. MODIFYING ALL PRIMARY/ALTERNATE DRIVE MOTORS WITH HEATING ELEMENT, TOGETHER WITH REPLACEMENT OF ALL CIRCUIT BREAKERS PROTECTING THIS SYS, AND A TEST OF THE PRIMARY MOTOR'S INTERNAL FUSE PROTECTION ON A RECURRING BASIS ALONG WITH THE PRESENT INSPECTION/CHKS ON THE JACKSCREW ASSEMBLY ON THE DC9/MD80 ACFT. A RECURRING DETAILED INSPECTION OF THE SWITCHES LOCATED IN THE R-HAND SIDE OF THE FORWARD SIDE OF THE FORWARD CARGO PIT. THESE SWITCHES ARE FOR HORIZ STABILIZER POS INDICATOR AND AUTOPLT PITCH SERVO. ANY WEAR OF STOPS, WORN SWITCHES IN THIS AREA CAN EVOLVE INTO A CATASTROPHE IF UNCHKED OR UNATTENDED TO.

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.