Judging from earlier cases, readers should be skeptical about any ThReverser interaction before this latest ENGINE SEPARATION. See history of B737-200 cases.
Cone pins were used on B737-100s and -200s, and B727s (fuse pins employed on B747, B767, B757, and B737-300/400/500s).
NTSB sought hardware changes. A safety cable system had previously been used to hold engine after failure of primary structure -- then secondary support structure designed and installed (which also fractured in the DAL case).
[See also B707 and B747 cases where #3 Eng separates and then spears the #4 Eng.]
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Delta B737-200
7Jan92 DFW. Engine separation on takeoff. After T/O at 200' breakaway safety bolts called "Cone Pins" sheared for right engine. Engine bounced on grass on right side of runway.
http://www.ntsb.gov/ntsb/brief.asp?e...11X13985&key=1
... FTW92IA055 ....
... DELTA AIR LINES ...
... Tuesday, January 07, 1992 in DFW ...
... BOEING 737-232 ... N322DL ...
THE RIGHT ENGINE SEPARATED ... CLIMBING THROUGH 200 FEET AFTER TAKEOFF. ... UNEVENTFUL LANDING ...
ENGINE SEPARATION WAS THE RESULT OF THE
FAILURE OF THE AFT CONE BOLT AND THE ENGINE SECONDARY SUPPORT ASSEMBLY. THE AFT CONE BOLT FAILED AS RESULT OF A PREEXISTING
FATIGUE CRACK, WHILE THE ENGINE
SECONDARY SUPPORT ASSEMBLY FAILED AS RESULT OF THE
DYNAMIC LOADS THAT EXCEEDED THE DESIGNED CAPACITY OF THE MOUNTING BOLTS.
THE TWO FORWARD CONE BOLTS FAILED IN OVERLOAD AS THE ENGINE SWUNG FORWARD DURING THE SEPARATION SEQUENCE.
METALLURGICAL TESTING REVEALED THAT THE FATIGUE OF THE AFT CONE BOLT WAS A RESULT OF LUBRICANT INADVERTENTLY INTRODUCED INTO THE CONICAL SURFACE OF THE CONE BOLT.
...Board determines the probable cause ...
THE FAILURE OF THE AFT CONE BOLT AS RESULT OF PREEXISTING FATIGUE CRACKING DUE TO IMPROPER MAINTENANCE, AND THE FAILURE OF THE SECONDARY SUPPORT STRUCTURE AS A RESULT OF LOADS THAT EXCEEDED THE CAPACITY OF THE ATTACHING HARDWARE AND THE CRUSHABLE HONEYCOMB CORE.
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Piedmont Airlines B737-200,
20Jan89, right engine separated from aircraft after T/O at Chicago. Newly designed secondary support structure had not yet been installed.
http://www.ntsb.gov/ntsb/brief.asp?e...13X27558&key=1
... CHI89MA046 ....
... PIEDMONT AIRLINES
... Friday, January 20, 1989 in CHICAGO, IL ...
... BOEING 737-201 ... N242US ...
AN IN-FLIGHT TEARAWAY OF THE RIGHT ENGINE (FROM THE RIGHT WING) OCCURRED AS THE AIRPLANE LIFTED OFF FROM THE RUNWAY. ... CONTINUED THE TAKEOFF ... RETURNED ...
AN EXAM OF ITS WING & SEPARATED ENGINE REVEALED THE
AFT CONE (ENG MOUNTING)
BOLT HAD FAILED FROM
FATIGUE, THEN THE TWO
FORWARD CONE BOLTS FAILED FROM DUCTILE OVERSTRESS.
A RAISED MECHANICAL DEFORMATIVE WAS FOUND ON THE CONICAL SURFACE OF THE AFT BOLT. THE DEFORMITY WAS INDICATIVE OF DAMAGE PRODUCED PRIOR TO OR DURING ASSEMBLY OF THE CONE BOLT IN THE ISOLATION MOUNT. A MATCHING CAVITY WAS NOTED ON THE ISOLATION MOUNT. THERE WAS EVIDENCE THAT THE MECHANICAL IRREGULARITY RESULTED IN A NONUNIFORM FIT WHICH
ALLOWED THE TORQUED FITTING TO LOOSEN DURING CYCLIC LOADING.
AD 88-01-07 REQUIRED THAT ULTRASONIC INSPECTION OF THE CONE BOLTS BE PERFORMED AT INTERVALS NOT TO EXCEED 600 CYCLES. AN ULTRASONIC INSPECTION OF THE BOLTS HAD BEEN ACCOMPLISHED ABOUT 330 CYCLES BEFORE THE ENGINE SEPARATED.
... Board determines the probable cause ...
PREVIOUS DAMAGE TO THE AFT CONE (ENGINE MOUNTING) BOLT, WHICH RESULTED IN MISMATCHED SURFACES BETWEEN THE BOLT AND ISOLATION MOUNT,
LOSS OF TORQUE DURING CYCLIC LOADING OF THE MOUNTING BOLT, AND SUBSEQUENT FATIGUE FAILURE OF THE BOLT.
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US Air B737-200 PHL
5Dec87 #2 engine separated shortly after takeoff. Cracks caused by metal fatigue in one of three bolts; after rear bolt failed the two forward bolts and support cable failed in overload.
http://www.ntsb.gov/ntsb/brief.asp?e...13X32769&key=1
... NYC88FA050 ....
... USAIR
... Saturday, December 05, 1987 ... DEPTFORD, NJ ...
... BOEING 737-2B7 ... N319AU ...
DRG TKOF, AS USAIR FLT 224 WAS CLBG THRU 4000', THE ACFT YAWED/ROLLED RGT. SIMULTANEOUSLY, THE CREW NOTICED THE #2 THROTTLE SLAM/LOCK TO THE IDLE PSN & A CONTINUOUS AIRFRAME BUFFET BEGAN.
SOON THEREAFTER, THE #2 ENG SEPD FM THE ACFT & THE BUFFET STOPPED.
THE ENG IMPACTED IN AN OPEN FLD, 6 MI FM THE ARPT.
JUST BFR IT SEPD, A PAX SAW THE AFT END OF THE #2 ENG MOMENTARILY DROOP ABOUT 30 DEG.
AFTER ENG SEPN, THE 'B' HYD SYS LOST PRES & THE TE FLAPS WOULD ONLY EXTD 10 DEG.
THE ACFT WAS LNDD SAFELY AFTER AN EMERG GEAR EXTN & DIFFERENTIAL BRAKING WAS USED FOR STEERING.
AN EXAM REVEALED THE
AFT MOUNT CONE BOLT FOR THE #2 ENG HAD FAILED FM
FATIGUE THRU THE THREAD RELIEF UNDERCUT RADIUS. FATIGUE CRACKS HAD INITIATED ON DIAMETRICALLY OPPOSITE SIDES OF THE RADIUS. SUBSEQUENTLY, THE
FWD MOUNT CONE BOLTS & SECONDARY SUPPORT CABLE FAILED FROM
OVERLOAD.
... Board determines the probable cause ...
ENGINE INSTALLATION, MOUNTING BOLT ..FATIGUE
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"Southwest 223" /
3Jan86 B737-2H4, after T/O from Love Field (Dallas), Rt Engine rear mount Cone Bolt sheared, mount failed and restraining cable broke; leaving the engine attached by only the two fwd mount bolts; returned safely. [AWST 124:31 Ja 13'86, photo.]
http://www.ntsb.gov/ntsb/brief.asp?e...10X00187&key=1
... FTW86MA030
... SOUTHWEST ...
... January 03, 1986 in DALLAS, TX
... BOEING 737-2H4 ... N86SW ...
THIS INCIDENT OCCURRED WHEN THE NO. 2 ENGINE EXPERIENCED AN
AFT ENGINE MOUNT CONE BOLT FAILURE AND THE SUBSEQUENT
FAILURE OF THE SECONDARY SUPPORT LINK (
STAINLESS STEEL CABLE).
THE FAILURE OF BOTH AFT ENGINE SUPPORT ASSEMBLIES DURING THE TAKEOFF ROLL ALLOWED THE AFT SECTION OF THE ENG TO HANG DOWN TO WITHIN 4' [sic, transcription err] OF THE GROUND. AS A RESULT, THE NO.2 THRUST REVERSER ACTUATOR ASSEMBLY DRUG THE RUNWAY ON ROTATION.
... RETURNED ... LANDED...
METALLURGICAL EXAMINATION OF THE
CONE BOLT REVEALED THAT IT FAILED AS A RESULT OF
FATIGUE, MOST PROBABLY DUE TO IMPROPER INSTALLATION OF THE BOLT, SPECIFICALLY, THAT IT WAS
UNDER TORQUED WHEN THE OPERATOR RE-INSTALLED THE ENG.
THE
SAFETY CABLE FAILED AS A RESULT OF
OVERSTRESS, PROBABLY INDUCED WHEN THE ACFT ENCOUNTERED A ROUGH STRETCH OF RUNWAY DURING THE TAKEOFF ROLL.
... Board determines the probable cause ...
ENGINE INSTALLATION, SUSPENSION MOUNTS .. FAILURE, PARTIAL
... FATIGUE ... SEPARATION ... OVERLOAD ... UNDERTORQUED
MAINTENANCE, INSTALLATION .. IMPROPER ...
Contributing Factors ... RUNWAY / LANDING AREA CONDITION ... ROUGH /UNEVEN