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SWA1380 - diversion to KPHL after engine event

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SWA1380 - diversion to KPHL after engine event

Old 19th Nov 2019, 19:16
  #442 (permalink)  
 
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Abstract of Final Report

Recommendations

To the Federal Aviation Administration


1. Require Boeing to determine the critical fan blade impact location(s) on the CFM56-7B
engine fan case and redesign the fan cowl structure on all Boeing 737 next-generation
series airplanes to ensure the structural integrity of the fan cowl after a fan-blade-out event.

2. Once the actions requested in Safety Recommendation [1] are completed, require Boeing
to install the redesigned fan cowl structure on new-production 737 next-generation-series
airplanes.

3. Once the actions requested in Safety Recommendation [1] are completed, require operators
of Boeing 737 next-generation-series airplanes to retrofit their airplanes with the
redesigned fan cowl structure.

4. Expand the Title 14 Code of Federal Regulations Part 25 and 33 certification requirements
to mandate that airplane and engine manufacturers work collaboratively to (1) analyze all
critical fan blade impact locations for all engine operating conditions, the resulting fan
blade fragmentation, and the effects of the fan-blade-out-generated loads on the nacelle
structure and (2) develop a method to ensure that the analysis findings are fully accounted
for in the design of the nacelle structure and its components.

5. Develop and issue guidance on ways that air carriers can mitigate hazards to passengers
affected by an in-flight loss of seating capacity.
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Old 19th Nov 2019, 19:31
  #443 (permalink)  
 
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NTSB Board Meeting: Southwest Airlines Flight 1380 Investigation
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Old 20th Nov 2019, 09:47
  #444 (permalink)  
 
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Originally Posted by Zeffy View Post
Final Report not yet published, to try to save anyone else the trouble of looking for it:-)

"NTSB staff is currently making final revisions to the report from which the attached conclusions and safety recommendations have been extracted."
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Old 20th Nov 2019, 13:23
  #445 (permalink)  
 
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https://www.cnbc.com/2019/11/19/ntsb...-accident.html

Boeing commits to NTSB safety fixes on thousands of 737 NG jets after deadly Southwest engine blast

Boeing on Tuesday said it plans to revamp parts for thousands of 737s after federal safety officials investigating last year’s deadly engine blast on Southwest Airlines flight called for a redesign that would better withstand engine failures in flight...

...Boeing said it commended the NTSB for its investigation and said it is “committed to working closely with the FAA, engine manufacturers, and industry stakeholders to implement enhancements that address the NTSB’s safety recommendations.”

It said “enhancements are being introduced” to inlet and fan cowls to improve “their ability to withstand an engine fan blade out event as well as to increase the overall capability of these structures.”
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Old 21st Nov 2019, 12:21
  #446 (permalink)  
 
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So the engine nacelle won't contain a blade failure. Are the rudder cables on the 737 NG vulnerable to blade impact damage, or is that a Max specific issue?

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Old 21st Nov 2019, 12:32
  #447 (permalink)  
 
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Originally Posted by SLF3 View Post
So the engine nacelle won't contain a blade failure. Are the rudder cables on the 737 NG vulnerable to blade impact damage, or is that a Max specific issue?
NO, nothing to do with the the recommendations at hand
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Old 21st Nov 2019, 16:04
  #448 (permalink)  
 
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Originally Posted by SLF3 View Post
So the engine nacelle won't contain a blade failure. Are the rudder cables on the 737 NG vulnerable to blade impact damage, or is that a Max specific issue?
Yes, they are, to all models of 737. That may not be WHY Boeing is getting busy with the cowling issue, but the cables will be somewhat better protected if the cowling improvements work.

One issue is how FAA managers agreed during certification of the 737 MAX to give Boeing a pass on complying with a safety rule that requires more separation between duplicate sets of cables that control the jet’s rudder.This is to avoid the possibility that shrapnel from an uncontained engine blowout could sever all the cables and render the plane uncontrollable.The requirement was introduced when such a blowout caused the deadly 1989 crash of a United Airlines DC-10 in Sioux City, Iowa. The 737 has never been brought into line with the requirement, and when Boeing updated to the 737 MAX it argued once again that design “changes would be impractical” and expressed concern about the potential impact on “resources and program schedules,” according to documents submitted to the FAA.
https://www.seattletimes.com/busines...87-dreamliner/
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Old 7th Dec 2019, 08:03
  #449 (permalink)  
 
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New additions to the Docket:

​​​​​​1 Dec 05, 2019 Party Submission - SWA 14 pages
2 Dec 05, 2019 Party Submission - Collins 7 pages
3 Dec 05, 2019 Party Submission - CFM 29 pages
4 Dec 05, 2019 Party Submission - Boeing 21 pages
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Old 7th Dec 2019, 16:01
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NTSB Board Investigation SWA 1380 -blancolirio

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Old 7th Dec 2019, 20:38
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Originally Posted by Takwis View Post
Yes, they are, to all models of 737. That may not be WHY Boeing is getting busy with the cowling issue, but the cables will be somewhat better protected if the cowling improvements work.

https://www.seattletimes.com/busines...87-dreamliner/
No, the control cable issue isn't fan blades and their associated debris. The cable issue is for an uncontained disc failure - which by definition won't be contained by the nacelle or engine structure (Where will a 1/3 fan disc go? Anywhere it wants to ).
The issue at hand is the failure of the inlet after the Fan Blade Out event. The containment ring worked as intended and contained all the high energy blade debris. However some of the low energy debris traveled forward and damaged the inlet (which didn't happen when they did the FBO test ~25 years ago), combined with higher than expected imbalance loads caused the inlet structure to fail. The damage to the fuselage was caused by the inlet, not the fan blade debris. Big parts departing the engine are a bit no-no since they can cause major damage to other parts of the airframe (the tail being the big concern):
the stresses in the fan cowl were greater than those calculated in the certification analyses. Since the time that the CFM56-7B engine and the Boeing 737-700 airplane were certificated (in December 1996 and December 1997, respectively), new technologies and analytical methods have been developed that will better predict the interaction of the engine and airframe during an FBO event and the response of the inlet, fan cowl, and associated airplane structures.
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Old 8th Dec 2019, 14:40
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Originally Posted by tdracer View Post
... The damage to the fuselage was caused by the inlet, not the fan blade debris. ...:
You are correct it was not fan blade fragments that broke the window. However, the window was actually struck by a section of the fan cowl door that held the heavy latch structure. When the fan blade released, it happened to hit at a clock position that gave a huge force and displacement to the bottom of the fan case. There is an unusual latch beam support connection to the fan case on this engine due to the flat bottom of the nacelle shape. The support is intended to keep the fan cowl doors tightly up against the engine. When the case in this area was driven outward, it directly transmitted load to the doors and latches and broke the doors open. A piece from the bottom latch end of one of the doors was slung at the fuselage and struck the window area, breaking the one window.
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Old 8th Dec 2019, 14:55
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Originally Posted by Dave Therhino View Post
You are correct it was not fan blade fragments that broke the window. However, the window was actually struck by a section of the fan cowl door that held the heavy latch structure. When the fan blade released, it happened to hit at a clock position that gave a huge force and displacement to the bottom of the fan case. There is an unusual latch beam support connection to the fan case on this engine due to the flat bottom of the nacelle shape. The support is intended to keep the fan cowl doors tightly up against the engine. When the case in this area was driven outward, it directly transmitted load to the doors and latches and broke the doors open. A piece from the bottom latch end of one of the doors was slung at the fuselage and struck the window area, breaking the one window.
Taken together with tdracerr post above, the individual details in the subject event are obviously repeatable for a number of reasons not all related to a CFM56 Fan blade failure. Thus the corrective actions as recommended are only minimizations of combinations. Taken in total the end result in this case is very improbable to re-occur. No doubt the manufacturers proposed actions are positive, but in the grand scheme of flight safety are not really news worthy.
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Old 8th Dec 2019, 20:54
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Possibly the worst threat posed by a fan blade failure with an inlet separation from a probabilistic standpoint is fuel exhaustion on an extended range flight. If a fan blade fails (which often depressurizes the fuselage due to intermediate fragments) and the inlet comes off during a step climb halfway between the West Coast and Hawaii, there is not enough fuel on board to make land due to the high drag of the failed nacelle.
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Old 8th Dec 2019, 21:52
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Originally Posted by Dave Therhino View Post
Possibly the worst threat posed by a fan blade failure with an inlet separation from a probabilistic standpoint is fuel exhaustion on an extended range flight. If a fan blade fails (which often depressurizes the fuselage due to intermediate fragments) and the inlet comes off during a step climb halfway between the West Coast and Hawaii, there is not enough fuel on board to make land due to the high drag of the failed nacelle.
Of all the non-contained fan blade fragments(only) that pierced the fuselage I don't recall one where pressurization was lost. A whistling sound was reported though

Losing an inlet cowl might also result in less drag. At any rate it has certainly happened before even with large fan engines and no control problems reported by the pilot
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Old 9th Dec 2019, 05:25
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Both the recent Pensacola and Philadelphia 737 CFM56-7B fan blade failures that caused inlet separations depressurized the fuselage. The skin on the 737 is quite a bit thinner than the skin of the larger airplanes. The pilot in the Philadelphia event reported significant control challenges. The drag study was done and the drag of a nacelle with the inlet missing is significantly greater than that of an intact nacelle with a windmilling engine. The critical scenario for setting ETOPS fuel reserves on a West Coast to Hawaii flight is an engine failure that causes depressurization at the critical point (equal time point). That required fuel is calculated based on the drag of an intact nacelle.
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Old 9th Dec 2019, 16:27
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Originally Posted by Dave Therhino View Post
There is an unusual latch beam support connection to the fan case on this engine due to the flat bottom of the nacelle shape.
Thank you for some illuminating and interesting posts. Since the unusual flattened nacelle shape is to fit the engine under the wing, are we to conclude then that this is another incident that is actually down to the short legs of the 737 and the desire to not redesign them for cost/ease-of-certification reasons?
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Old 9th Dec 2019, 17:32
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Originally Posted by Dave Therhino View Post
Both the recent Pensacola and Philadelphia 737 CFM56-7B fan blade failures that caused inlet separations depressurized the fuselage. The skin on the 737 is quite a bit thinner than the skin of the larger airplanes. The pilot in the Philadelphia event reported significant control challenges. The drag study was done and the drag of a nacelle with the inlet missing is significantly greater than that of an intact nacelle with a windmilling engine. The critical scenario for setting ETOPS fuel reserves on a West Coast to Hawaii flight is an engine failure that causes depressurization at the critical point (equal time point). That required fuel is calculated based on the drag of an intact nacelle.
You are mixing in events that have released more than fan blades that resulted in loss of pressurization
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Old 10th Dec 2019, 01:22
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In the Pensacola event I believe it was a fan blade fragment that depressurized the airplane.

I was simply pointing out that, while the fuel load required for an engine failure that depressurizes the airplane is covered by the ETOPS fuel reserve rules, the fuel required if you add drag from a nacelle with a severely damaged or missing inlet is not covered.
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Old 10th Dec 2019, 02:32
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Originally Posted by Dave Therhino View Post
In the Pensacola event I believe it was a fan blade fragment that depressurized the airplane.

I was simply pointing out that, while the fuel load required for an engine failure that depressurizes the airplane is covered by the ETOPS fuel reserve rules, the fuel required if you add drag from a nacelle with a severely damaged or missing inlet is not covered.
Ir was a disk uncontainment along with its blades, quite a bit more robust than a fan blade release. A fan blade release simply doesn't have the energy to make a big hole in a pressurized cabin.
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