Narrative:

New problems with the thrust reversers started as soon as the stage 3 modules program started. On feb/xx/95, the seventh unit that was modified came into the shop for repairs. The carriage had failed. We had never seen this type of failure before and when the factory was contacted they reported that they had never seen this happen before and wanted the broken part to examine. The carriage broke at the hydraulic cylinder attach point. Apart from the broken carriage what was really shocking was the appearance of the entire thrust reverser. It was if the whole thing had been in a sooty fire. The mounting hardware had corroded and the structure had a burnt and corroded look. Soot and heat had migrated forward into the shell of the reverser. We knew right away there was a big problem with the stage 3 mod. We started having a whole list of problems including, warning light problems, delamination of the acoustical panels, corrosion, hydraulic actuator leaks, and the list goes on. Our company started working with the stc holder on ways to fix the problems. They were not helpful to say the least. Over time, 2 band-aid type fixes were put into the modules on a retrofit program. They have helped but didn't fix the problems. We are now in the third phrase of a retrofit program to fix the mod. It seems to be working. Soot, corrosion and heat problems seem to be better, however, the delamination problem looks like it's here to stay. It would take 20 pages to explain everything that has happened with this mod. Our biggest concern now is the structure corrosion. We aren't getting help from the manufacturer or the stc holder. The units coming into the shop now for maintenance are showing too much heat stress and corrosion, especially at the door support attach fitting. There are several carriers operating aircraft with forms of this module and I can't say for sure if they are as worried with the corrosion problem as we are. As I said, this is just a quick overview of this situation and I wanted to express my concern. Callback conversation with reporter revealed the following information: the reporter states the stage 3 thrust reverser modification has been going on for almost 3 yrs and the reporter is assigned to the shop that builds up and repairs the thrust reverser modules. The reverser modules began returning to the shop for rebuild not long after installation with types of failure never seen on thrust reversers before, broken fittings, heat damage, delamination and corrosion. The reporter stated little or no help was available from the corporation holding the supplemental type certificate and the aircraft manufacturer refers any questions back to the holder of the stc. Reporter advised only the engine manufacturer was concerned about the engine parameter shifts with the stage 3 thrust reversers, engine overboost and high fuel flows which were observed in the test cells before installation were later corrected with a narrowing of the exhaust tailpipe. The reporter said the major problem now is delamination and corrosion caused by the extensive sooting which when mixed with rain and heat creates an acid condition. The reporter stated that the upper reverser section will normally run 100 degrees centigrade higher then the lower section which causes heat stress.

Google
 

Original NASA ASRS Text

Title: CONCERNED MECHS ACCOMPLISHING STAGE 3 THRUST REVERSER MODIFICATIONS FOR THE MLG ACFT ARE RPTING NUMEROUS FAILURES AND SERIOUS PROBS WITH THE RETROFIT PROGRAM.

Narrative: NEW PROBS WITH THE THRUST REVERSERS STARTED AS SOON AS THE STAGE 3 MODULES PROGRAM STARTED. ON FEB/XX/95, THE SEVENTH UNIT THAT WAS MODIFIED CAME INTO THE SHOP FOR REPAIRS. THE CARRIAGE HAD FAILED. WE HAD NEVER SEEN THIS TYPE OF FAILURE BEFORE AND WHEN THE FACTORY WAS CONTACTED THEY RPTED THAT THEY HAD NEVER SEEN THIS HAPPEN BEFORE AND WANTED THE BROKEN PART TO EXAMINE. THE CARRIAGE BROKE AT THE HYD CYLINDER ATTACH POINT. APART FROM THE BROKEN CARRIAGE WHAT WAS REALLY SHOCKING WAS THE APPEARANCE OF THE ENTIRE THRUST REVERSER. IT WAS IF THE WHOLE THING HAD BEEN IN A SOOTY FIRE. THE MOUNTING HARDWARE HAD CORRODED AND THE STRUCTURE HAD A BURNT AND CORRODED LOOK. SOOT AND HEAT HAD MIGRATED FORWARD INTO THE SHELL OF THE REVERSER. WE KNEW RIGHT AWAY THERE WAS A BIG PROB WITH THE STAGE 3 MOD. WE STARTED HAVING A WHOLE LIST OF PROBS INCLUDING, WARNING LIGHT PROBS, DELAMINATION OF THE ACOUSTICAL PANELS, CORROSION, HYD ACTUATOR LEAKS, AND THE LIST GOES ON. OUR COMPANY STARTED WORKING WITH THE STC HOLDER ON WAYS TO FIX THE PROBS. THEY WERE NOT HELPFUL TO SAY THE LEAST. OVER TIME, 2 BAND-AID TYPE FIXES WERE PUT INTO THE MODULES ON A RETROFIT PROGRAM. THEY HAVE HELPED BUT DIDN'T FIX THE PROBS. WE ARE NOW IN THE THIRD PHRASE OF A RETROFIT PROGRAM TO FIX THE MOD. IT SEEMS TO BE WORKING. SOOT, CORROSION AND HEAT PROBS SEEM TO BE BETTER, HOWEVER, THE DELAMINATION PROB LOOKS LIKE IT'S HERE TO STAY. IT WOULD TAKE 20 PAGES TO EXPLAIN EVERYTHING THAT HAS HAPPENED WITH THIS MOD. OUR BIGGEST CONCERN NOW IS THE STRUCTURE CORROSION. WE AREN'T GETTING HELP FROM THE MANUFACTURER OR THE STC HOLDER. THE UNITS COMING INTO THE SHOP NOW FOR MAINT ARE SHOWING TOO MUCH HEAT STRESS AND CORROSION, ESPECIALLY AT THE DOOR SUPPORT ATTACH FITTING. THERE ARE SEVERAL CARRIERS OPERATING ACFT WITH FORMS OF THIS MODULE AND I CAN'T SAY FOR SURE IF THEY ARE AS WORRIED WITH THE CORROSION PROB AS WE ARE. AS I SAID, THIS IS JUST A QUICK OVERVIEW OF THIS SIT AND I WANTED TO EXPRESS MY CONCERN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATES THE STAGE 3 THRUST REVERSER MODIFICATION HAS BEEN GOING ON FOR ALMOST 3 YRS AND THE RPTR IS ASSIGNED TO THE SHOP THAT BUILDS UP AND REPAIRS THE THRUST REVERSER MODULES. THE REVERSER MODULES BEGAN RETURNING TO THE SHOP FOR REBUILD NOT LONG AFTER INSTALLATION WITH TYPES OF FAILURE NEVER SEEN ON THRUST REVERSERS BEFORE, BROKEN FITTINGS, HEAT DAMAGE, DELAMINATION AND CORROSION. THE RPTR STATED LITTLE OR NO HELP WAS AVAILABLE FROM THE CORPORATION HOLDING THE SUPPLEMENTAL TYPE CERTIFICATE AND THE ACFT MANUFACTURER REFERS ANY QUESTIONS BACK TO THE HOLDER OF THE STC. RPTR ADVISED ONLY THE ENG MANUFACTURER WAS CONCERNED ABOUT THE ENG PARAMETER SHIFTS WITH THE STAGE 3 THRUST REVERSERS, ENG OVERBOOST AND HIGH FUEL FLOWS WHICH WERE OBSERVED IN THE TEST CELLS BEFORE INSTALLATION WERE LATER CORRECTED WITH A NARROWING OF THE EXHAUST TAILPIPE. THE RPTR SAID THE MAJOR PROB NOW IS DELAMINATION AND CORROSION CAUSED BY THE EXTENSIVE SOOTING WHICH WHEN MIXED WITH RAIN AND HEAT CREATES AN ACID CONDITION. THE RPTR STATED THAT THE UPPER REVERSER SECTION WILL NORMALLY RUN 100 DEGS CENTIGRADE HIGHER THEN THE LOWER SECTION WHICH CAUSES HEAT STRESS.

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.