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  #1  
Old 07-21-2017, 05:16 PM
BillL BillL is offline
 
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Default NTSB Final Issued for N307AB

Remember to follow DR's Rules.

RV7A Hurricane, UT - Inflight breakup.

NTSB Final https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA

Accident number if that link does not work. WPR16F A036

Decidedly unsatisfying conclusion, but not sure what else they could have concluded.

Edit - Mod: Thanks for the relocation.
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Last edited by BillL : 07-21-2017 at 06:40 PM.
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  #2  
Old 07-21-2017, 06:23 PM
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RV8JD RV8JD is offline
 
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From the NTSB Report:
"Control continuity was established from the cockpit controls to the elevators and the right aileron. The left aileron controls cables were fractured and had a splayed, broom-strawed appearance, consistent with tension overload. The rudder cables were jammed somewhere in the fuselage, and control continuity could not be established, but the cables remained attached at the rudder and the pedals."
Not quite right!
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  #3  
Old 07-21-2017, 07:28 PM
BillL BillL is offline
 
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Is there a technical reason for the VS with upper rudder attached to have settled to earth well in advance of the HS (L & R)? The report states the HS failed first, separated (and from the debris field) landed closer to the main site.
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  #4  
Old 08-10-2017, 01:54 PM
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grubbat grubbat is offline
 
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Default Tail question

Bill, I'm would guess the obivious that the tail separated first and thus the reason it's the fartherest away from main crash site. As to the reason of why it came off, well, I guess even the NTSB didn't want to speculate. The fact that it departed first is interesting. I wonder how many occurances of tail separations by type have occurred. My memory isn't what it used to be but I suspect the -3,-4,-6, -9, and -10 do not have the same frequency. If the tail separation causes can't be determined, would it be insane to assume that the data will get better over time without any changes ( that is, less tail separations occurances)?


Quote:
Originally Posted by BillL View Post
Is there a technical reason for the VS with upper rudder attached to have settled to earth well in advance of the HS (L & R)? The report states the HS failed first, separated (and from the debris field) landed closer to the main site.
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  #5  
Old 09-02-2017, 07:34 PM
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Thermos Thermos is offline
 
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Quote:
Originally Posted by grubbat View Post
I wonder how many occurances of tail separations by type have occurred. My memory isn't what it used to be but I suspect the -3,-4,-6, -9, and -10 do not have the same frequency.
I've kept track of structures-related accidents in RVs in general, but my focus is obviously on the -7.

There have been two other RV-7/7A tail separation accidents in recent memory that appear to be similar to this one. One was a Canadian RV-7A, C-GNDY, which was investigated by the Canadian Transportation Safety Board. A later one was an RV-7A, N174BK, in New Jersey, which was investigated by the NTSB. Both of those accidents had much more data available from which to draw a conclusion, so in this case I think the NTSB did the best they could with what they had.

At the risk of being accused of speculation by a mod, all three of these accidents were "big tail" RV-7As, i.e., with RV-9 rudders, and according to the accident reports, were estimated to be well above Vne (20-35 kts) when structural failure occurred. The RV-7's rear fuselage and stabilizer structure is very similar to the RV-8, and given the relatively greater use of the -8 for aerobatics, and the probability that some have been past Vne, should we expect to have seen similar accidents in the -8? Of course, that question leave a lot of factors out like build quality, pilot training, usage spectrum, sample size, etc.

I'm forced to wonder if the combination of the -7 VS and -9 rudder may be less robust than with the original -7/ current -8 rudder, but the bottom line is still to fly your airplane inside the design speed/weight/CG envelope.

Dave
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Last edited by Thermos : 09-02-2017 at 07:42 PM.
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  #6  
Old 09-02-2017, 07:50 PM
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catmandu catmandu is offline
 
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Very astute observation, Dave. Thanks.
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  #7  
Old 07-22-2017, 01:52 AM
rv8ch rv8ch is offline
 
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Quote:
Originally Posted by RV8JD View Post
From the NTSB Report:
"Control continuity was established from the cockpit controls to the elevators and the right aileron. The left aileron controls cables were fractured and had a splayed, broom-strawed appearance, consistent with tension overload. The rudder cables were jammed somewhere in the fuselage, and control continuity could not be established, but the cables remained attached at the rudder and the pedals."
Not quite right!
I'll say. That's an amazing error. Perhaps a copy/paste error from another report?
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  #8  
Old 07-24-2017, 12:43 PM
BillL BillL is offline
 
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Default Error to be corrected, now let's focus on the issues.

I just spoke with Albert Nixon the chief investigator for this report. I pointed out the error regarding the controls cables vs control rods. He was very appreciative and said he will get it corrected in all the locations in the report. It might take a few days to get all the processes executed, but will get through the system right away.

FOLLOW UP EDIT: The NTSB report was modified on August 9th.
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Last edited by BillL : 09-03-2017 at 06:53 PM. Reason: follow up on NTSB error correction
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  #9  
Old 07-24-2017, 01:50 PM
RViter RViter is offline
 
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If I read it right, the VS and upper rudder was found at the beginning of the debris field but there was nothing specific about the condition of those components, nor the attach points seen in the report. Indications of how they separated from the aft fuselage?

The separation of the upper rudder and VS from the lower rudder might suggest an examination of the inboard portion of the elevators to see if there was contact with the lower rudder (deflection into either elevator)?

Just 1st impressions. But they seem to be associated with the earliest breakup events.
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  #10  
Old 07-25-2017, 10:48 AM
BillL BillL is offline
 
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Quote:
Originally Posted by RViter View Post
If I read it right, the VS and upper rudder was found at the beginning of the debris field but there was nothing specific about the condition of those components, nor the attach points seen in the report. Indications of how they separated from the aft fuselage?

The separation of the upper rudder and VS from the lower rudder might suggest an examination of the inboard portion of the elevators to see if there was contact with the lower rudder (deflection into either elevator)?

Just 1st impressions. But they seem to be associated with the earliest breakup events.
I have been mentally processing, so may be wrong here - - the report indicates that the HS failed first. Assuming that is correct, I am guessing it was sudden and unlikely that both sides failed perfectly in harmony. Given that one side might fail suddenly, there would be a very high release of that load on the spar, twisting the fuse and bending the VS spars to near instant failure. If so, I then might imagine the VS leveraging against the rudder and separating it below the center pivot. The report stated it pulled out the TE rivets. There may have been some flapping there, as the rudder CW separated early and went ballistic, landing near the main body of the plane. (some confusion about exactly what induced CW separation if the remainder of the upper rudder came down with the VS.)

I believe the report did state that the remaining rudder showed impact with the elevators.
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