Narrative:

It was the first flight of the day and the WX was hazy but very smooth as we descended on downwind for landing at dtw. We asked the controller how long of a final we might expect and were told about 10 mi. We were at 250 KTS descending clean through about 8000 ft. The controller asked if we could see the airport and we answered that we could. He cleared us for a visual. At that time, we were about 4 - 4 1/2 mi from the end of the runway at about 6000 ft. I deployed the speed brake and allowed the airspeed to bleed off to 210 KTS. This gave me a good rate of descent without the excessive deck angles associated with high speed (250 KTS) use of the speed brake. I smoothly rolled the aircraft to base leg and as I was preparing to roll back level, we heard a very loud bang and felt a severe jolt through the airframe. I felt an acceleration and noticed that the airspeed was up 10 KTS to 220 KTS and that the normal speed brake vibration ceased. After the usual expressions of, 'now, what do you suppose that was?' we began to troubleshoot. I initially thought, based on the bang and jolt, that we had hit something or that something had fallen from the aircraft. However, the lack of vibration indicated that we were clean and structurally intact. We noticed that the speed brake light on the instrument panel was extinguished although the handle remained in the extend position. I concluded that we had broken an actuator or had some other mechanical failure in the speed brake -- a quick check of hydraulic pressure and fluid -- normal and steady. The flight attendants rang expressing concern and we advised them that the noise was an abnormal speed brake retraction and nothing to worry about. Since the aircraft was flying normally, except for no speed brake, and since we were now on final approach only a few mi from touchdown, I concluded that it was unnecessary to call out the equipment. Therefore, I did not declare an emergency and we landed normally. All appropriate abnormal and normal checklists were accomplished. The crew adhered to all applicable FARS and company procedures. Following the flight, the station wanted to MEL the speed brake and send us back to pit. I refused insisting that someone inspect the interior of the tail section. The mechanics crawled up into the tail section and found the damage. I put on a mechanic's jumpsuit and crawled into the tail to inspect the damage myself. I found that the massive hydraulic actuator arm was bent into a shallow 'U' shape. The upper cylinder support fitting was bent upward at about a 30 degree angle. The hydraulic lines were bent and wrapped around the cylinder, which was supported only by its stabilizing rod assembly and the mangled hydraulic lines. The electrical connections to the actuating solenoid were severed and open wires were hanging from the unit. The lower retaining pin was hanging out and judging from the way the upper support fitting being bent and the rust on the lower retaining pin, I believe that the actuator unit had been held in place for some time by only the upper pin. I called the F100 equipment manager on the phone to advise him of the situation and to recommend that we inspect the fleet for other pin failures. Callback conversation with reporter revealed the following information: reporter captain called back subsequent to the report being completed and even an FAA telecom item. Both the analyst who worked the report and the analyst who briefed the report for the FAA tried to call the reporter numerous times. However, he did call back with not much additional information. The captain reporter thinks that his company did a fleet inspection of the fokker 100's and no other aircraft had evidence of similar failures. The failed speed brake hydraulic actuator appeared to have been deteriorating for some time by the appearance of the lower attaching pin which appeared to have worn and fallen out. That resulted in the hydraulic actuator detaching and breaking electrical lines as well as bending the steel hydraulic line. The hydraulic lines were not broken, but bent around the actuator. Reporter then faxed copies of the fokker 100 illustrated parts catalog. Reporter captain believes that the mounting of the hydraulic pump is a design flaw and should have been mounted horizontally vice vertically.

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Original NASA ASRS Text

Title: A FOKKER 100 ON FINAL APCH EXPERIENCED FAILURE OF THE AFT FUSELAGE SPD BRAKE SYS.

Narrative: IT WAS THE FIRST FLT OF THE DAY AND THE WX WAS HAZY BUT VERY SMOOTH AS WE DSNDED ON DOWNWIND FOR LNDG AT DTW. WE ASKED THE CTLR HOW LONG OF A FINAL WE MIGHT EXPECT AND WERE TOLD ABOUT 10 MI. WE WERE AT 250 KTS DSNDING CLEAN THROUGH ABOUT 8000 FT. THE CTLR ASKED IF WE COULD SEE THE ARPT AND WE ANSWERED THAT WE COULD. HE CLRED US FOR A VISUAL. AT THAT TIME, WE WERE ABOUT 4 - 4 1/2 MI FROM THE END OF THE RWY AT ABOUT 6000 FT. I DEPLOYED THE SPD BRAKE AND ALLOWED THE AIRSPD TO BLEED OFF TO 210 KTS. THIS GAVE ME A GOOD RATE OF DSCNT WITHOUT THE EXCESSIVE DECK ANGLES ASSOCIATED WITH HIGH SPD (250 KTS) USE OF THE SPD BRAKE. I SMOOTHLY ROLLED THE ACFT TO BASE LEG AND AS I WAS PREPARING TO ROLL BACK LEVEL, WE HEARD A VERY LOUD BANG AND FELT A SEVERE JOLT THROUGH THE AIRFRAME. I FELT AN ACCELERATION AND NOTICED THAT THE AIRSPD WAS UP 10 KTS TO 220 KTS AND THAT THE NORMAL SPD BRAKE VIBRATION CEASED. AFTER THE USUAL EXPRESSIONS OF, 'NOW, WHAT DO YOU SUPPOSE THAT WAS?' WE BEGAN TO TROUBLESHOOT. I INITIALLY THOUGHT, BASED ON THE BANG AND JOLT, THAT WE HAD HIT SOMETHING OR THAT SOMETHING HAD FALLEN FROM THE ACFT. HOWEVER, THE LACK OF VIBRATION INDICATED THAT WE WERE CLEAN AND STRUCTURALLY INTACT. WE NOTICED THAT THE SPD BRAKE LIGHT ON THE INST PANEL WAS EXTINGUISHED ALTHOUGH THE HANDLE REMAINED IN THE EXTEND POS. I CONCLUDED THAT WE HAD BROKEN AN ACTUATOR OR HAD SOME OTHER MECHANICAL FAILURE IN THE SPD BRAKE -- A QUICK CHK OF HYD PRESSURE AND FLUID -- NORMAL AND STEADY. THE FLT ATTENDANTS RANG EXPRESSING CONCERN AND WE ADVISED THEM THAT THE NOISE WAS AN ABNORMAL SPD BRAKE RETRACTION AND NOTHING TO WORRY ABOUT. SINCE THE ACFT WAS FLYING NORMALLY, EXCEPT FOR NO SPD BRAKE, AND SINCE WE WERE NOW ON FINAL APCH ONLY A FEW MI FROM TOUCHDOWN, I CONCLUDED THAT IT WAS UNNECESSARY TO CALL OUT THE EQUIP. THEREFORE, I DID NOT DECLARE AN EMER AND WE LANDED NORMALLY. ALL APPROPRIATE ABNORMAL AND NORMAL CHKLISTS WERE ACCOMPLISHED. THE CREW ADHERED TO ALL APPLICABLE FARS AND COMPANY PROCS. FOLLOWING THE FLT, THE STATION WANTED TO MEL THE SPD BRAKE AND SEND US BACK TO PIT. I REFUSED INSISTING THAT SOMEONE INSPECT THE INTERIOR OF THE TAIL SECTION. THE MECHS CRAWLED UP INTO THE TAIL SECTION AND FOUND THE DAMAGE. I PUT ON A MECH'S JUMPSUIT AND CRAWLED INTO THE TAIL TO INSPECT THE DAMAGE MYSELF. I FOUND THAT THE MASSIVE HYD ACTUATOR ARM WAS BENT INTO A SHALLOW 'U' SHAPE. THE UPPER CYLINDER SUPPORT FITTING WAS BENT UPWARD AT ABOUT A 30 DEG ANGLE. THE HYD LINES WERE BENT AND WRAPPED AROUND THE CYLINDER, WHICH WAS SUPPORTED ONLY BY ITS STABILIZING ROD ASSEMBLY AND THE MANGLED HYD LINES. THE ELECTRICAL CONNECTIONS TO THE ACTUATING SOLENOID WERE SEVERED AND OPEN WIRES WERE HANGING FROM THE UNIT. THE LOWER RETAINING PIN WAS HANGING OUT AND JUDGING FROM THE WAY THE UPPER SUPPORT FITTING BEING BENT AND THE RUST ON THE LOWER RETAINING PIN, I BELIEVE THAT THE ACTUATOR UNIT HAD BEEN HELD IN PLACE FOR SOME TIME BY ONLY THE UPPER PIN. I CALLED THE F100 EQUIP MGR ON THE PHONE TO ADVISE HIM OF THE SIT AND TO RECOMMEND THAT WE INSPECT THE FLEET FOR OTHER PIN FAILURES. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR CAPT CALLED BACK SUBSEQUENT TO THE RPT BEING COMPLETED AND EVEN AN FAA TELECOM ITEM. BOTH THE ANALYST WHO WORKED THE RPT AND THE ANALYST WHO BRIEFED THE RPT FOR THE FAA TRIED TO CALL THE RPTR NUMEROUS TIMES. HOWEVER, HE DID CALL BACK WITH NOT MUCH ADDITIONAL INFO. THE CAPT RPTR THINKS THAT HIS COMPANY DID A FLEET INSPECTION OF THE FOKKER 100'S AND NO OTHER ACFT HAD EVIDENCE OF SIMILAR FAILURES. THE FAILED SPD BRAKE HYD ACTUATOR APPEARED TO HAVE BEEN DETERIORATING FOR SOME TIME BY THE APPEARANCE OF THE LOWER ATTACHING PIN WHICH APPEARED TO HAVE WORN AND FALLEN OUT. THAT RESULTED IN THE HYD ACTUATOR DETACHING AND BREAKING ELECTRICAL LINES AS WELL AS BENDING THE STEEL HYD LINE. THE HYD LINES WERE NOT BROKEN, BUT BENT AROUND THE ACTUATOR. RPTR THEN FAXED COPIES OF THE FOKKER 100 ILLUSTRATED PARTS CATALOG. RPTR CAPT BELIEVES THAT THE MOUNTING OF THE HYD PUMP IS A DESIGN FLAW AND SHOULD HAVE BEEN MOUNTED HORIZLY VICE VERTLY.

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.