+---------------+------------------------------------------------------+
| **Accident**  | Boeing 747 SR-100 [**(Figure                         |
|               | 1)**](#Fig_1)[]{#Return_From_Fig_1 .anchor}, Japan   |
|               | Airlines Flight 123/Registration JA8119              |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+
| **Location**  | Gunma Prefecture, Japan                              |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+
| **Date**      | August 12, 1985                                      |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+
| **Summary**   | On August 12, 1985, the flight departed Tokyo bound  |
|               | for Osaka at about 18:10 local time. At about 18:24, |
|               | at 24,000 feet and 300 knots, a bang, vibration, and |
|               | cabin decompression was recorded on the cockpit      |
|               | voice recorder.                                      |
|               |                                                      |
|               | The captain was in the right seat and the co-pilot   |
|               | was in the left seat for training as captain. 46     |
|               | seconds later, the captain signaled an emergency on  |
|               | the transponder and requested a return to Tokyo.     |
|               |                                                      |
|               | The aircraft descended to 22,000 feet and began      |
|               | 2-minute Phugoid (longitudinal) and Dutch roll       |
|               | (lateral) oscillatory motions. The flight crew was   |
|               | unable to control heading or pitch through normal    |
|               | flight control inputs. Steering and pitch attitude   |
|               | were accomplished with thrust changes.               |
|               |                                                      |
|               | The flight crew maintained 22,000 feet and 250 knots |
|               | for about 20 minutes.                                |
|               |                                                      |
|               | At 18:39, the main landing gear extended and Dutch   |
|               | roll increased in severity.                          |
|               |                                                      |
|               | The airplane did a slow left turn while descending   |
|               | through 8,000 feet. Severe roll and pitch            |
|               | oscillations continued. The flight crew saw          |
|               | mountains at 18:47 and increased thrust. Altitude    |
|               | was 5,300 feet.                                      |
|               |                                                      |
|               | The crew began to extend flaps at 18:51 and the roll |
|               | amplitude increased to a 60 degree bank angle. At    |
|               | this point, the crew began flap retraction and added |
|               | thrust. Altitude was 10,000 feet and the aircraft    |
|               | began a steep nose down descent at 18,000            |
|               | feet/minute. They recovered to a nose up position.   |
|               |                                                      |
|               | See [Figure 2](#Fig_2)[]{#Return_From_Fig_2 .anchor} |
|               | for maps of the flight path.                         |
|               |                                                      |
|               | At 18:56, the airplane struck mountains at 5,000     |
|               | feet altitude and 340 knots forty-six minutes        |
|               | following takeoff from Tokyo and 32 minutes          |
|               | following the decompression event.                   |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+

+---------------+------------------------------------------------------+
| **Summary     | 505 passengers and 15 crew members were killed. Four |
| (continued)** | survivors were found near the tail section that had  |
|               | broken away from the main wreckage field. Ground     |
|               | fire destroyed the majority of the aircraft.         |
|               |                                                      |
|               | Much of the airplane\'s vertical tail and aft        |
|               | section were lost from the airplane following the    |
|               | decompression event. See [Figure                     |
|               | 3](#Fig_3)[]{#Return_From_Fig_3 .anchor} for a       |
|               | photograph taken by a witness prior to the crash. It |
|               | shows the missing sections of the airplane.          |
|               |                                                      |
|               | The airplane was delivered January 30, 1974. S/N     |
|               | 20783, equipped with four Pratt and Whitney JT9D-7A  |
|               | Engines. Total Time 25,030 hours. Total landings     |
|               | 18,835. The airplane was used for short routes       |
|               | within Japan with high capacity seat configuration.  |
|               | The airplane was on its fifth flight of the day.     |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+
| **Accident    | The accident was investigated by the Japan Ministry  |
| Board         | of Transport\'s Aircraft Accident Investigation      |
| Findings**    | Commission. They issued their aircraft accident      |
|               | investigation report on June 19, 1987.               |
|               |                                                      |
|               | The accident was caused by deterioration of flying   |
|               | quality and loss of primary flight control functions |
|               | due to a rupture of the airplane\'s aft pressure     |
|               | bulkhead and the subsequent rupture of part of the   |
|               | fuselage tail, vertical fin and all four hydraulic   |
|               | lines and loss of all primary flight control         |
|               | functions. The empennage structure that departed the |
|               | airplane as a result of the pressure bulkhead        |
|               | failure is shown in [Figure                          |
|               | 4](#Fig_4)[]{#Return_From_Fig_4 .anchor}. See        |
|               | [Figure 5](#Fig_5)[]{#Return_From_Fig_5 .anchor} and |
|               | [Figure                                              |
|               | 6](#figure-6-747-rear-fuselage)[]{#Return_From_Fig_6 |
|               | .anchor} for detailed illustrations of the rear      |
|               | fuselage.                                            |
|               |                                                      |
|               | The aft pressure bulkhead ruptured because fatigue   |
|               | cracks propagating from the spliced section of the   |
|               | bulkhead\'s web weakened the bulkhead to the extent  |
|               | that it could no longer endure the in-flight cabin   |
|               | pressure.                                            |
|               |                                                      |
|               | The initiation and propagation of the fatigue cracks |
|               | are attributable to the improper repairs of the      |
|               | bulkhead conducted in 1978. The fact that the        |
|               | fatigue cracks were not found in the later           |
|               | maintenance inspections contributed to their         |
|               | propagation leading to the rupture of the bulkhead.  |
|               |                                                      |
|               | See [Figure 7](#Fig_7)[]{#Return_From_Fig_7          |
|               | .anchor}, which shows how the cracks propagated from |
|               | rivet to rivet. The single (middle) rivet row became |
|               | the origin of structural fatigue cracking. The       |
|               | cracks connected rivet-to-rivet and propagated       |
|               | through the \"crack stop\" straps. The \"modified\"  |
|               | splice error could not be found through visual       |
|               | inspection since the gap was filled with fillet      |
|               | sealant. The \"correct\" and \"incorrect\"           |
|               | configurations would appear identical when viewed    |
|               | from either side.                                    |
|               |                                                      |
|               | See [Figure 8](#Fig_8)[]{#Return_From_Fig_8 .anchor} |
|               | for an illustration showing how the repair should    |
|               | have been made versus how it was actually made.      |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+
| **Accident    | On June 2, 1978, during a landing incident at Osaka, |
| Board         | the airplane experienced a tail strike. Several aft  |
| Findings      | fuselage frames, skin, and aft pressure bulkhead     |
| (continued)** | were damaged. At the time, the airplane had 16,200   |
|               | hours and 12,300 cycles. The airplane was repaired   |
|               | by a Boeing Airplane on-ground team contracted to    |
|               | perform damage repair.                               |
|               |                                                      |
|               | They replaced/repaired a major portion of the aft    |
|               | fuselage, replaced the lower half of the pressure    |
|               | bulkhead, and replaced the tail compartment pressure |
|               | relief door.                                         |
|               |                                                      |
|               | Post repair inspection showed inadequate edge margin |
|               | on the newly replaced lower half of the bulkhead.    |
|               | The solution for the inadequate edge margin involved |
|               | installation of a splice plate to join upper and     |
|               | lower halves of the bulkhead. The rework design      |
|               | called for a single splice plate to be used.         |
|               | However, the splice plate actually installed on the  |
|               | accident airplane involved cutting the splice plate  |
|               | into two pieces in order to \"fit\". This resulted   |
|               | in a single row of rivets transferring the load to   |
|               | the upper affected web plate instead of two rows, as |
|               | specified in the repair instruction drawing. This    |
|               | caused the bulkhead web to be improperly loaded and  |
|               | susceptible to early fatigue. Select here to see an  |
|               | animation of this effect.                            |
|               |                                                      |
|               | Furthermore, because of the geometry of the repair   |
|               | and the use of fillet sealant to fill the gap, the   |
|               | splice error could not be found through visual       |
|               | inspection. Correct and incorrect configurations     |
|               | would appear identical when viewed from either side. |
|               |                                                      |
|               | The accident board estimated that the strength of    |
|               | the repair decreased to about 70% of the strength    |
|               | that would have resulted from a proper repair.       |
|               |                                                      |
|               | See [Figure 9](#Fig_9)[]{#Return_From_Fig_9          |
|               | .anchor}, which shows the area of the aft pressure   |
|               | bulkhead that was repaired.                          |
|               |                                                      |
|               | The Boeing 747 SR-100 cabin pressure differential is |
|               | selectable by the flight crew at: 8.9 psi for high   |
|               | altitude/long range flights or 6.9 psi for low       |
|               | altitude/short range flights. The JAL structural     |
|               | inspection intervals were predicated on low          |
|               | altitude/short range flights (6.9 psi) however, JAL  |
|               | regularly operated at 8.9 psi.                       |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+

+---------------+------------------------------------------------------+
| **Accident    | According to the English translation of the          |
| Board         | \"Aircraft Accident Investigation Report on Japan    |
| Findings      | Air Lines JA8119, Boeing 747 SR-100,\" JAL made a    |
| (continued)** | study, at the time of the introduction of the Boeing |
|               | 747SR, on the fatigue life of the pressurization     |
|               | fuselage under its standard operational mode. As a   |
|               | result of the study, JAL estimated that the fatigue  |
|               | life would be about 6% shorter when the cabin        |
|               | pressurization selector switch is always set to 8.9  |
|               | psi than it would be if the switch is selected to    |
|               | either 8.9 psi or 6.9 psi depending on cruising      |
|               | altitude. It is possible that the fatigue life could |
|               | have been impacted by more than 6%. In any event,    |
|               | maintenance schedules should reflect actual          |
|               | operational situations.                              |
|               |                                                      |
|               | It was estimated that the airplane flew              |
|               | unpressurized at altitudes of more than 20,000 feet  |
|               | from the time of the decompression for about 18      |
|               | minutes without the crew wearing oxygen masks. From  |
|               | the cockpit voice recorder, it was clear that        |
|               | judgment was being impaired, probably from hypoxia.  |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+
| **Accident    | The National Transportation Safety Board (NTSB) made |
| Board         | the following safety recommendations to the FAA.     |
| Reco          |                                                      |
| mmendations** | **Recommendation A-85-133 - December 5, 1985**       |
|               |                                                      |
|               | Require the manufacturer to modify the design of the |
|               | Boeing 747 empennage so that in the event that a     |
|               | significant pressure buildup occurs in the normally  |
|               | unpressurized empennage, the structural integrity of |
|               | the stabilizers and their respective control         |
|               | surfaces will be protected against catastrophic      |
|               | failure, and to incorporate associated modifications |
|               | on all Boeing 747 airplanes. Airworthiness Directive |
|               | (AD) 86-08-02 was issued to address this             |
|               | recommendation (see below for a discussion of this   |
|               | AD).                                                 |
|               |                                                      |
|               | **Recommendation A-85-134 - December 5, 1985**       |
|               |                                                      |
|               | Require the manufacturer to modify the design of the |
|               | Boeing 747 hydraulic systems so that in the event a  |
|               | significant pressure buildup occurs in the normally  |
|               | unpressurized empennage, the integrity of all four   |
|               | hydraulic systems will not be impaired, and to       |
|               | incorporate associated modifications on all Boeing   |
|               | 747 airplanes. AD 87-12-04 was issued to address     |
|               | this recommendation (see below for a discussion of   |
|               | this AD).                                            |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+

+---------------+------------------------------------------------------+
| **Accident    | **Recommendation A-85-135 - December 5, 1985**       |
| Board         |                                                      |
| Re            | Reevaluate the design of the Boeing 747 and 767 aft  |
| commendations | pressure bulkheads by requiring Boeing to analyze    |
| (continued)** | and test further the bulkhead to demonstrate the     |
|               | validity of the fail-safe \"flapping\" failure mode. |
|               | This recommendation was incorporated into            |
|               | recommendation A-85-138.                             |
|               |                                                      |
|               | **Recommendation A-85-136 - December 5, 1985**       |
|               |                                                      |
|               | Evaluate any procedures approved to repair Boeing    |
|               | 747 and Boeing 767 aft pressure bulkheads to assure  |
|               | that the repairs do not affect the \"fail-safe\"     |
|               | concept of the bulkhead design, which is intended to |
|               | limit the area of pressure relief in the event of a  |
|               | structural failure.                                  |
|               |                                                      |
|               | The Structural Repair Manuals for the Boeing Models  |
|               | 707, 737, 747, and 767 were reviewed. The FAA found  |
|               | they do not contain any instructions that would be   |
|               | in conflict with the \"fail-safe\" concept.          |
|               |                                                      |
|               | **Recommendation A-85-137 - December 5, 1985**       |
|               |                                                      |
|               | Revise the inspection program for the Boeing 747     |
|               | rear pressure bulkhead to establish an inspection    |
|               | interval wherein inspections beyond the routine      |
|               | visual inspection would be performed to detect the   |
|               | extent of possible multiple site fatigue cracking.   |
|               |                                                      |
|               | As a result, Boeing issued Service Bulletin          |
|               | 747-53-2275 requesting a visual inspection from the  |
|               | aft side of the pressure bulkhead at 1,000           |
|               | flight-cycle intervals (for freighters) or at 2,000  |
|               | flight cycle intervals for passenger airplanes. They |
|               | further recommended after 20,000 flight-cycles that  |
|               | a detailed inspection by high-precision eddy         |
|               | current, ultrasonic wave and x-rays be accomplished  |
|               | at 2,000 flight-cycle intervals (freighters) or at   |
|               | 4,000 flight-cycle intervals for passenger           |
|               | airplanes.                                           |
|               |                                                      |
|               | **Recommendation A-85-138 - December 5, 1985**       |
|               |                                                      |
|               | Determine which transport category airplanes have    |
|               | dome-shaped aft pressure bulkheads and ascertain     |
|               | that the \"fail-safe\" criteria for the pressure     |
|               | bulkheads of those airplanes have been               |
|               | satisfactorily evaluated.                            |
+---------------+------------------------------------------------------+

+---------------+------------------------------------------------------+
| **Accident    | Fatigue testing and damage tolerance testing were    |
| Board         | completed on the Boeing 747 in March and July 1986   |
| Re            | respectively. A reinforced aft pressure bulkhead was |
| commendations | installed from line number 672, delivered in         |
| (continued)** | February 1987. The modification added two tear       |
|               | straps, a cover plate to the center of the bulkhead, |
|               | and doublers to both sides of the bulkhead around    |
|               | the APU cutout.                                      |
|               |                                                      |
|               | ###                                                  |
|               |                                                      |
|               | ### Recommendation A-85-139 - December 5, 1985       |
|               |                                                      |
|               | Evaluate any procedures approved to repair the aft   |
|               | pressure bulkhead of any airplanes which incorporate |
|               | a dome-type of design to assure that the effected    |
|               | repair does not derogate the fail-safe concept of    |
|               | the bulkhead. AD 85-22-12 was issued to address this |
|               | recommendation (see below for a discussion of this   |
|               | AD).                                                 |
|               |                                                      |
|               | ### Recommendation A-85-140 - December 5, 1985       |
|               |                                                      |
|               | Issue a maintenance alert bulletin to persons        |
|               | responsible for the engineering approval of repairs  |
|               | to emphasize that the approval adequately consider   |
|               | the possibility of influence on ultimate failure     |
|               | modes or other fail-safe design criteria.            |
|               |                                                      |
|               | The FAA issued Action Notice 8110.7, Approved Data,  |
|               | on November 18, 1986. It provides guidance to        |
|               | airworthiness inspectors on approval of major        |
|               | repairs and major alterations.                       |
+---------------+------------------------------------------------------+
|               | ###                                                  |
+---------------+------------------------------------------------------+
| **Unsafe      | The following unsafe conditions existed at the time  |
| Conditions**  | of this accident.                                    |
|               |                                                      |
|               | 1.  Lack of independence of four hydraulic systems   |
|               |     from single failure event (zonal hazard).        |
|               |                                                      |
|               | 2.  Vulnerability of tail compartment to             |
|               |     catastrophic damage resulting from explosive     |
|               |     decompression (inadequate venting).              |
|               |                                                      |
|               | 3.  Aft pressure bulkhead structural fatigue failure |
|               |     characteristics (i.e., crack propagation through |
|               |     tear stop straps).                               |
|               |                                                      |
|               | 4.  Improper repair of aft pressure bulkhead         |
|               |     significantly reduced the strength of the        |
|               |     bulkhead.                                        |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+

+---------------+------------------------------------------------------+
| **Design and  | The following design and safety assumptions proved   |
| Safety        | to be flawed.                                        |
| Assumptions** |                                                      |
|               | -   The failure mode of the pressure bulkhead would  |
|               |     be a single section flapping failure mode.       |
|               |     Circumferential straps designed to prevent more  |
|               |     than one sector from failing (i.e., crack        |
|               |     stopper) were installed. The theory is that if a |
|               |     crack is initiated and propagated, it can be     |
|               |     detected and repaired while its propagation      |
|               |     remains in one bay. A bay is defined as one area |
|               |     of the pressure bulkhead surrounded by           |
|               |     stiffeners and tear straps. In this case, cracks |
|               |     initiated and propagated simultaneously in more  |
|               |     than one bay, they were difficult to detect      |
|               |     because they were small and propagated along     |
|               |     rivet holes at web overlaps. Therefore, in this  |
|               |     case, the tear stop strap did not prevent a      |
|               |     crack from progressing into multiple sections.   |
|               |     During the airplane design phase, the            |
|               |     configuration of tear stop straps installed on a |
|               |     compound curved panel (like the pressure         |
|               |     bulkhead) was not adequately tested. Since the   |
|               |     accident, tear strap testing has occurred and    |
|               |     tear straps have been significantly improved.    |
|               |                                                      |
|               | -   The design of the tail compartment pressure      |
|               |     relief vent door (the capacity of the door) was  |
|               |     predicated on aft pressure bulkhead failure with |
|               |     panel failure assumed to result in flapping of   |
|               |     bay. The actual level of pressure venting into   |
|               |     the compartment was significantly greater than   |
|               |     predicted. Vent door capacity and function are   |
|               |     now verified by test.                            |
|               |                                                      |
|               | -   The independence of four hydraulic control       |
|               |     systems was assumed. No zonal hazard analysis    |
|               |     was performed on the torque box location.        |
|               |                                                      |
|               | -   It was assumed that if a crack in the pressure   |
|               |     bulkhead propagated to a certain length, it      |
|               |     could be detected by a visual inspection such as |
|               |     leakage of pressurized air from the crack and    |
|               |     abnormality of the web. It is thought by the     |
|               |     investigation team that it was difficult to      |
|               |     detect the fatigue cracks of the accident        |
|               |     airplane by visual inspection or by air leakage  |
|               |     because the cracks were small and propagated     |
|               |     along rivet holes at web overlaps.               |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+
| *             | There was one major precursor to this accident. On   |
| *Precursors** | October 2, 1971, a British European Airways Vickers  |
|               | 951 Vanguard airplane on a flight from London to     |
|               | Salzburg experienced a structural failure of the     |
|               | rear pressure bulkhead at an altitude of 5,000       |
|               | meters. The aircraft spiraled down out of control    |
|               | and crashed in a field near Aarsele, Belgium killing |
|               | all 55 passengers and 8 crew members.                |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+

+---------------+------------------------------------------------------+
| **Precursors  | Examination of the airplane revealed corrosion in    |
| (continued)** | the lower part of the rear pressure bulkhead         |
|               | underneath plating that was bonded to the structure. |
|               | The bond was completely delaminated in this area and |
|               | the bulkhead material literally eaten away. Tears    |
|               | ran upward and outward form the corroded area. The   |
|               | corrosion had probably required a relatively long    |
|               | period of time to develop, and gave way on this      |
|               | particular flight to the stress created by           |
|               | pressurization. When the bulkhead ruptured, air from |
|               | the cabin rushed into the empennage, which was not   |
|               | designed to withstand such internal pressure.        |
|               | Interior damage and severe distortion of the outer   |
|               | skin led to the failure of the tail surfaces causing |
|               | the airplane to enter a steep dive, from which       |
|               | recovery was impossible.                             |
|               |                                                      |
|               | The corrosion was attributed to fluid contamination. |
|               | It was not detectable through the normal maintenance |
|               | procedures which consisted of both visual and        |
|               | radiographic inspection.                             |
|               |                                                      |
|               | Subsequent to the accident, similar corrosion was    |
|               | found in eight other aircraft of the same type in    |
|               | Vanguard\'s fleet. Inspection procedures were        |
|               | revised and the airplane modified to improve access  |
|               | to the inspected area. The frequency of inspections  |
|               | was increased considerably.                          |
|               |                                                      |
|               | This accident like the JAL 123 accident, resulted    |
|               | from a ruptured aft pressure bulkhead, which         |
|               | destroyed much of the control surface of the tail    |
|               | section. The rupture was preceded by fatigue         |
|               | cracking that was never detected during inspections  |
|               | because it was very difficult to detect.             |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+
| **Resulting   | No regulatory changes were made because this         |
| ACs,          | accident resulted from an incorrect repair.          |
| Regulatory    |                                                      |
| Guidance and  |                                                      |
| Policy**      |                                                      |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+
| **            | The following airworthiness directives were issued   |
| Airworthiness | as a result of this accident. View the ADs in the    |
| Directives    | FAA\'s Regulatory and Guidance Library at:           |
| Issued**      | <http://www.airweb.faa.gov/Regulatory_and_Guidance_  |
|               | Library/rgWebcomponents.nsf/HomeFrame?OpenFrameSet>. |
|               |                                                      |
|               | AD 85-22-12 required a one-time visual inspection of |
|               | the aft side of the aft pressure bulkhead for        |
|               | evidence of repairs or damage. It further required   |
|               | reporting of a complete description of the findings  |
|               | (sketches, photos, or drawings, as necessary) of the |
|               | inspections.                                         |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+
| **            | AD 86-08-02 was issued on April 4, 1986. This AD     |
| Airworthiness | became effective on May 19, 1986 and was applicable  |
| Directives    | to all Boeing Model 747 series airplanes. It         |
| Issued        | requires the addition of a structural cover for the  |
| (continued)** | opening within the empennage, which provides access  |
|               | to the vertical fin. This is to prevent structural   |
|               | failure of the vertical fin in the event of failure  |
|               | of the aft pressure bulkhead.                        |
|               |                                                      |
|               | On May 26, 1987, the FAA issued AD 87-12-04 to       |
|               | require installation of a hydraulic fuse in the      |
|               | number 4 hydraulic system on Boeing Model 747 series |
|               | airplanes. The AD became effective on July 13, 1987. |
|               |                                                      |
|               | AD 87-23-10 was effective December 10, 1987 and      |
|               | required inspection for damage and cracking of the   |
|               | aft pressure bulkhead on Boeing Model 747 airplanes. |
|               | This AD was later superseded by AD 98-20-20 which    |
|               | added repetitive inspections AD 98-20-20 was, in     |
|               | turn, superseded by AD 2000-15-08, which requires    |
|               | that a one-time inspection to detect cracking of the |
|               | upper segment of the bulkhead web be accomplished    |
|               | repetitively, and adds additional repetitive         |
|               | inspections to detect cracking of the upper and      |
|               | lower segments of the aft bulkhead web.              |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+
| ## Le         | The following lessons should be learned from         |
| ssons Learned | studying the crash of Japan Airlines Flight 123.     |
|               |                                                      |
|               | -   Validate/confirm failure mode assumptions.       |
|               |                                                      |
|               | -   Aircraft maintenance programs should be          |
|               |     developed consistent with actual aircraft        |
|               |     operations.                                      |
|               |                                                      |
|               | -   Repairs should be accomplished in a manner that  |
|               |     preserves the original safety features of the    |
|               |     airplane. Technical coordination among           |
|               |     appropriate safety experts may be necessary.     |
|               |                                                      |
|               | -   System isolation can be compromised by lack of   |
|               |     physical separation although functional          |
|               |     isolation exists.                                |
|               |                                                      |
|               | -   Communication between certification authorities  |
|               |     of different countries is often not very         |
|               |     effective and needs to be improved. Perhaps the  |
|               |     formation of an international database would be  |
|               |     a positive step toward better communication.     |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+

+---------------+------------------------------------------------------+
| **Category**  | Environmental Mechanical Aging Aircraft              |
|               |                                                      |
|               | Avionics Propulsion Human Factors                    |
|               |                                                      |
|               | Electrical Auxiliary, other Software                 |
|               |                                                      |
|               | Interior Airframe Environment                        |
|               |                                                      |
|               | Maintenance, Operations                              |
|               |                                                      |
|               | Regulations, policies, standards                     |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+
| **Application | Design & Certification Regulation, Policy, etc.      |
| of Lessons    |                                                      |
| Learned**     | ADs, TCs, etc. Continued Operational Safety          |
|               |                                                      |
|               | Maintenance Other:                                   |
|               | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_                 |
+---------------+------------------------------------------------------+
|               |                                                      |
+---------------+------------------------------------------------------+
| **Key Words** | Pressure Bulkhead, Crack Propagation, Vertical Fin,  |
|               | Decompression, Flapping, Tear Straps.                |
+---------------+------------------------------------------------------+

[]{#Fig_1 .anchor}**Figure 1: Boeing 747 SR-100 Airplane**

[(Select here to return)](#Return_From_Fig_1)

![](media/image1.jpeg){width="6.5in" height="4.55in"}

[]{#Fig_2 .anchor}**Figure 2: Flight Path of Japan Airlines Flight 123**

[(Select here to return)](#Return_From_Fig_2)

![](media/image2.jpeg){width="2.6979166666666665in"
height="2.0416666666666665in"}

![](media/image3.jpeg){width="6.498611111111111in"
height="5.725694444444445in"}

[]{#Fig_3 .anchor}**Figure 3: Witness Photograph of the Missing Tail and
Aft Section**

[(Select here to return)](#Return_From_Fig_3)

![](media/image4.jpeg){width="3.4902777777777776in"
height="2.102777777777778in"}

[]{#Fig_4 .anchor}**Figure 4: Drawing Showing Cross Hatch of Missing
Tail Section**

[(Select here to return)](#Return_From_Fig_4)

![](media/image5.jpeg){width="6.488888888888889in"
height="1.7416666666666667in"}

[]{#Fig_5 .anchor}**Figure 5: Boeing 747 Aft Pressure Bulkhead**

## [**(Select here to return)**](#Return_From_Fig_5)

![](media/image6.jpeg){width="4.93125in" height="6.986111111111111in"}

## Figure 6: 747 Rear Fuselage

[(Select here to return)](#Return_From_Fig_6)

![](media/image7.jpeg){width="6.492361111111111in"
height="4.344444444444444in"}

[]{#Fig_7 .anchor}**Figure 7: Fracture Line Propagating from Rivet to
Rivet**

[(Select here to return)](#Return_From_Fig_7)

The single (middle) rivet row became the origin of structural fatigue
cracking. Cracks connected rivet-to-rivet and propagated through "crack
stop" straps. The "modified" splice error could not be found through
visual inspection since gap was filled with fillet sealant. "Correct"
and "incorrect" configurations would appear identical when viewed from
either side.

![](media/image8.jpeg){width="6.25in" height="2.8020833333333335in"}

[]{#Fig_8 .anchor}**Figure 8: Planned Splice (Left) and Actual Splice
(Right)**

[(Select here to return)](#Return_From_Fig_8)

The initiation and propagation of the fatigue cracks are attributable to
the improper repairs of the bulkhead conducted in 1978. The fact that
the fatigue cracks were not found in the later maintenance inspections
contributed to their propagation leading to the rupture of the bulkhead.

This drawing shows the improper repair. The planned splice is shown on
the left and the actual splice is shown on the right. The splice plate
actually installed on the accident airplane involved cutting the plate
into two pieces in order to \"fit.\" This resulted in a single row of
rivets (in this case, the middle row) carrying flight loads rather than
two rows, as specified in the repair instruction drawing. The modified
splice could not be found through visual inspection since the gap was
filled with fillet sealant. Correct and incorrect configurations would
appear identical when viewed from either side.

![](media/image9.jpeg){width="5.4215277777777775in" height="5.75in"}

[]{#Fig_9 .anchor}**Figure 9: Area of the Aft Pressure Bulkhead that was
Repaired**

[(Select here to return)](#Return_From_Fig_9)

![](media/image10.jpeg){width="6.496527777777778in"
height="4.686805555555556in"}