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In a modern airliner, if the aft pressure bulkhead experiences a structural failure, what design features are incorporated into the empennage to prevent the empennage from being overpressurized (i.e. at or near cabin pressure vs the normal case, which is at or near outside pressure) to the point of structural failure? Or, in other words, what keeps the next aft pressure bulkhead failure from blowing the vertical tail, or some other important part, off the airplane a la JAL123?

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If what's escaping a compromised bulkhead is cabin pressure, not an explosion; the airframe structure aft of the pressure vessel is wide open for air to escape. The structure is hollow from one component to the next with "lightening holes" wherever possible designed to minimize weight (nothing to do with thunderstorm lightning). Additionally, the lightening holes provide for plumbing, wiring, maintenance, inspection access, and ventilation.

Unless there's an explosion or some catastrophic failure of the pressure vessel, escaping cabin pressure by itself cannot pressurize the open empennage. Pressurized aircraft also have a safety valve to protect the pressure vessel from structural damage in the event of outflow valve failure. The prospect of aft pressure bulkhead failure before other skin fracture is unlikely.

If you are able to peer in between the rudder and vertical stabilizer of an aircraft, you will likely see the openings.

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  • $\begingroup$ So it wasn't the failure if the aft pressure bulkhead in JAL-123 that caused the nearly complete failure of that plane's empennage? $\endgroup$ – BillDOe Jun 5 '17 at 19:51
  • $\begingroup$ The APB was damaged from a tailstrike event. The cause of JAL123 was attributed to improper repair of the APB and empennage following a tail strike. Overpressurization was not the cause. $\endgroup$ – STWilson Jun 5 '17 at 20:02
  • $\begingroup$ This from lessonslearned.faa.gov/… "The internal overpressure caused structural failures in critical fin support structure, causing it to rupture and depart the airplane." $\endgroup$ – BillDOe Jun 5 '17 at 20:07
  • $\begingroup$ The cabin was not over pressurized. The repairs to the APB and tailcone did not meet design criteria. The word "failure" here is used loosely to describe a sequence of events. Had the repairs and parts met design criteria and a rupture occurred, then there was a failure in respect to the part. What failed in this case was a repair process. $\endgroup$ – STWilson Jun 5 '17 at 20:19
  • $\begingroup$ @STWilson -- the cabin was indeed at normal pressure -- the APB failed, which overpressurized the empennage relative to outside pressure and caused the ensuing vertical tail failure $\endgroup$ – UnrecognizedFallingObject Jun 5 '17 at 22:21

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