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  #111  
Old 03-01-2006, 04:21 AM
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Kevin Horton Kevin Horton is offline
 
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Default

Quote:
Originally Posted by Ironflight
So what makes a risk acceptable? well, my first test is - do I understand it? do I understand what could happen, and how it it could happen. What are the odds of it happening? Next...do I have a way to survive if it DOES happen? (You might think the next question is "What's the worst that could happen" - but that's too easy - you do everything wrong, you die! Next question...) OK, so, for example, is there a risk mitigation for this particular failure? Sure - always keep one tank at least a third full (Gee, that is close to VFR reserves, isn't it?). If the engine quits, switch tanks and try a restart. Should work, unless you are so incredibly unlucky as to have them both fall off, and you have used your reserve fuel.
Paul,

Shouldn't the mitigation be to keep both tanks above one third full? You have no way to know which side the failure will happen on. If I run tank A down to a very low value, switch tanks, and have the failure happen on tank B, I'm in trouble, as there is very little fuel left in tank A.

I think the mitigation has to be to always have enough fuel in either tank so you could do a comfortable diversion on that tank alone, or one third full, whichever is greater. The amount of fuel required will depend on how far you are from a suitable airfield.
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  #112  
Old 03-01-2006, 06:25 AM
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Ironflight Ironflight is offline
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Default Well, that's right Kevin, if...

If you start with the assumption that BOTH tubes have already fallen off (or might have fallen off) and launch into the blue, then what you say is 100% correct (I was very tired after a long couple of days in sims when I typed that - a good argument for always having people check your work!). Then you have to assume the worst is there. Then you have to keep fuel above the outlet fitting on both tanks all the time. (Has anyone actually done the geometry to figure out what that level is? Someone who has their wing son, but their fuel sender out could fill until the gas dribbles out I guess, then tell us how much is inthe tank...but there is a fire hazard asociated with that !)

However...worst on worst is good for theoretical analysis - but rarely occurs in the real world. Roberta suggested a good way to see if your tubes are intact at this time. There are probably others. If you do that, you can have a fairly reasonable confidence that both aren't going to fall off on the same flight. It COULD happen, but the odds are going to be very low.

So you're absolutly correct - if you want to be absolutely sure. But that is kinda my point...there are so many other things that you can't be absolutely sure about...(Oh, I almost forgot - brake fires! We have had way more than one report of brake fires and subsequent wheel pant fires! No changes to prevent those...). If you want certainty, you can never leave the ground. Each person decides, whether consciously or not, what level of risk they are willing to assume. They are also obligated to not put others at risk without them being properly informed. I will always keep more fuel on board with a passenger until I can safety the fitting for instance.

Just be as safe and informed as you can be.

Paul
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  #113  
Old 03-01-2006, 07:46 AM
redbeardmark redbeardmark is offline
 
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Default regarding fuel levels

Paul,
You made a couple of good points there. If we don't safety the fuel intake nut, we should inform every passenger before every flight(think of it as "informed consent").

Also, sucking tanks down to VFR minimum fuel reserve is not a good idea until the nut is safetied. In fact, it really isn't a GOOD idea even if the nuts are safetied. VFR minimum fuel reserve is 30 minutes-- and if you're burning 9 gallons/hr, then you only have 4.5 gallons of fuel on board when you land. That ain't much. I would challenge anyone to come up with a solid argument to risk my beloved RV by intentionally flight planning and then flying until there was only 4.5 gallons left on board. Typically, I have at least 10 gallons on board when landing, so it is unlikely that I would ever suck fumes from one tank without having a bit more to draw from the other... unless both failed at the same time.

And very good point about the brake fires. Now that is something I actually think about.
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  #114  
Old 03-01-2006, 07:47 AM
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Default SBs

Quote:
Originally Posted by Ironflight
...(Oh, I almost forgot - brake fires! We have had way more than one report of brake fires and subsequent wheel pant fires! No changes to prevent those...)
Very true. And Van's still sells the most flammable brake fluid out there. That is a strange inconsistency.
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  #115  
Old 03-01-2006, 08:22 AM
Tom Maxwell Tom Maxwell is offline
 
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Default Risk Management

Thanks for the discussion Paul. Somehow I knew you would have some great input to the discussion. I love talking about the human psyche and our thought processes as they relate to rationalization of ideas, beliefs, and behaviors. I agree with a lot of what you say.

We all know that flight has its inherent risks and that engineering is largely a series of compromises. We also all agree that not every perceived or imaginable risk can nor should be eliminated prior to flight. I think you said it very eloguently that if this were the case we wouldn't get off the ground.

My point in bringing up the Challenger parallel was simply to point out that being a homosapien carries with it certain emotional pitfalls that may result in biased or clouded judgement. You are much closer to the NASA decision making process than probably anyone else on this forum so you know how decisions are made. What I have to go by are the documentaries and news reports (not always unbiased) that I have seen. I don't for one minute think that someone blatantly stood up and said, "Dang, those o-rings are totally unsafe but we are going to fly anyway." But I do believe that the decision to fly was biased by internal pressures to make up time on the flight schedule and to prevent further embarassment from yet another postponed flight. Again, I may be totally wrong on my understanding but I think this is the understanding of most people in the US and around the world.

So yes, I agree, we can never mitigate every POTENTIAL problem. But in the case of the Challenger, correct me if I am wrong, there was evidence of o-ring leakage on previous flights and the engineers concluded that the extremely cold weather (for Florida) would only exacerbate the problem. If this is true, it was not a case of not addressing every potential problem, but a case of letting the pressures to fly override clear evidence of a real and known problem and the recommendations of the designers.

I know there must be dozens of objections to flight on every mission and I suspect a great deal of them are simply CYA just in case something does happen. It is top managements job to filter through all of the objections and to match them up with real data to make the final go/no-go decision. I guess that is why top management are paid the big bucks. Yes hindsight is always 20/20 and I certainly am not saying that anyone maliciously put another human being's life in jeopardy, I don't think that for one minute. But from what I know, in the Challenger incident, the people making the decisions failed to tie the facts (known prior leakages) to the untested (unusually cold weather) to the concerns of the designing engineers (we can't guarantee they will hold) and as a result, people died. I don't subscribe to the notion of "fog of war" or "blaming society" or "institutional decision making" as I view these as excuses to keep from holding individuals accountable. I don't know for sure, but I suspect there were a significant number of individuals within NASA who could have stood up and said, "Hey, with what we know today, I will not endorse pushing the go button." Those responsible for making the final go/no-go decision and failing to do so are the ones I hold accountable for the death of the Challenger crew. What I suspect happened (only speculation based on my involvement in many corporate decision making scenarios) is that political pressure and the potential backlash of being labeled as "one standing in the way of getting a bird up" caused a lot of really smart people to override or simply not object to what they really understood to be a less than acceptable risk.

And that is the parallel I am making here. Van has identified what he consdiers, as the designer and producer of these airplanes, to be a serious enough problem to issue a mandatory SB. We can debate whether or not it should be an SB and we can debate whether or not Van is addressing a real problem or trying to cover his backside and we can try to second guess him and come up with what we think is a better solution and we can try to convince Van to change his mind. But this is not a democratic decision making process. The reality is that the SB is not based on what a majority of the builders think is best. The bottom line is that Van, after his careful thought and consideration and more knowledge about these planes than anyone else, has issued what he is calling a mandatory SB and he further qualifies it by stating that it should be completed prior to next flight. We as the flight directors and engineers of our aircraft must now take that data and make the go/no-go decisions for our birds.

I don't see this as addressing potential or imaginable problems at all. And we can try to poo-poo it away by saying, "What about the other upteen fittings in the plane and the flim-flam and the watch-a-ma-callit and the who-dunits? If they fail the plane is going into the ground as well." I say, "so what." This SB is addressing one specific real problem that has been identified and Van has determined to be serious enough to make it mandatory.

I tend to look for the good in people, but as we all know, a lot of good people (being human as they are) sometimes don't make the best decisions due to outside pressures or internal desires. We see this a lot in GA and all walks of life. In this regard, I think the decision that each builder makes is very much like the decision made in the Challenger situation. With all of our human quirks and biases, it is very difficult to step back and make a totally objective decision on whether to drill out and replace that rivet, replace that skin because a scratch is a little too deep, or the other thousands of decisions and compromises that must be made during the course of building an airplane. Over the years we have tried to remove the objectivity from these decisions by creating standards and guldelines. And in this case, Van (who I consider to be the final authority on these matters) has tried to help us out by making the decision for us. He has made his recommendation and all we can do is decide whether or not we will comply with his recommendation.

I know that if I were in a flying status, I would ground my bird and take the time, as inconvenient as it may be, to complete the SB.

Good luck to everyone and thanks Paul, I appreciate your knowledge and insight.
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  #116  
Old 03-01-2006, 09:15 AM
jcoloccia jcoloccia is offline
 
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Quote:
Originally Posted by Ironflight
But the real problem is not in identifying risks - it is in analyzing them.
You'll get no argument from me

Quote:
Originally Posted by Ironflight
...OK, sorry for all that - my point is - all flying entails some risks. You cannot, unfortunately, take the stand that you will not fly until every single risk has been eliminated. Or you can quit and take up gardening. That is NOT a devil-may-care attitude by the way - it is a realistic one. You will have to accept some risk.
Reread my post. It wasn't about flying at all. It was a about Vans decision to issue an SB.

Quote:
Originally Posted by Ironflight
...we never imagined that a dual-O-ring seal would fail." And because we couldn't imagine it, we didn't analyze it - we didn't calculate the risk, and our friends didn't come home.
I'm sorry, Paul, but I respectfully disagree. The evidence was all there and very clear. The lesson of Challenger is the slippery slope when you accept design failure as signs of success. O-ring degredation was typical on the shuttle flights. Okay, you never had total burn through, but you always had SOME. So someone analyzed it and saw (and I'm not using real numbers here) that it only got through, say, 15% of the first O-Ring. Somehow this got transformed into 85% "safety margin". Problem is, they weren't designed to degrade AT ALL, therefore the safety margin was actually negative per the design. The design failure was spun and turned into design success! Yes yes, this is all Monday monring quarterbacking and hindsight, but this isn't a critique of NASA at all. I think they do, and have done, a fine job across the board. It's a critical review of some of the things that went wrong so that we don't repeat it. It will have all been for nothing if we water it down and pretend it was just a big accident. It was a systematic breakdown of sound engineering. As it applyies to our little planes, we've been bashing Van for a week because of this useless, unnescesary, CYA SB. Why is it unnescessary? Why, because only a couple have come loose. Design success? The fact that any came loose is cause for concern since that's not what it's designed to do.

Quote:
Originally Posted by Ironflight
...It is not up to you to tell others if and when they should do it (although you can decline to ride with them if they have not).
I didn't even touch on this, and I wouldn't dream of telling anyone else what to do. Personally, I think as long as you're aware of the potential, this is mostly a non-issue. If it were me, I would simply safety wire it at my next annual.

So this isn't at all about flight safety or whether or not someone should perform the SB. It's about the faulty risk assesment that's been flying back and forth. Make the decisions for yourselves, but at least make it based on something other than "it's only happened a couple of times".
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Last edited by jcoloccia : 03-01-2006 at 09:29 AM.
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  #117  
Old 03-01-2006, 05:12 PM
redbeardmark redbeardmark is offline
 
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Default Where will it all end?

Maybe it is time to lighten up this thread and begin a listing of controversial topics with catchy titles:

1. the "B-nut"
2. the "O-ring"
3. the "dimpled chad"
4. the "magic bullet"
5...

Timless classics that we never grow weary of debating. Feel free to add to the list.
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  #118  
Old 03-01-2006, 06:03 PM
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Build9A Build9A is offline
 
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Quote:
Originally Posted by redbeardmark
Maybe it is time to lighten up this thread
This has been a fairly interesting thread. BUT, Vans has stated their position. Probably had some serious discussion among the team. Decided to issue the SB. Ignore it, inspect it, comply or wait. It's a pain in the #&* but, we all have the choice whether to do it or not. Since I've decided to wait till my full blown annual next month, (Like Paul) I'd like to see a new thread titled "here's some tips on complying with the fuel pick-up SB"
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  #119  
Old 03-02-2006, 03:41 PM
RV9AFlyer RV9AFlyer is offline
 
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Default QB's--the risk is this

My feeling is that most if not all QB kits and QB tanks where shipped with only hand tightened fuel pick-up tube fittings. This is how my RV-9A QB was shipped like others I have been reading about (see "Mandatory fuel tube bulletin" started by Fred... AND also "New mandatory fuel tube service bulletin SB-02-23" reply by Robertahegy). I upgraded my fuel tubes to the screen type tube that Van's sells, and I used EZ-Turn on the threads, making sure they where tight and properly aligned at assembly and install. However, the original tubes were loose, but I also assumed that I needed to tighten them after looking over the sub-assembly--that's just how I work.

Now, since I have not gotten any response from Van's on other loose QB tubes, I can assume that they know QB?s shipped have a problem. Until Van's can provide me with data showing that a properly tightened fuel tube fitting can come loose, I will continue flying unless I notice an issue with fuel pressure in either tank (have not seen this). The reason for that is because I know it was done correctly, and I think that there is more risk in opening up fuel tanks in my case, so I'm happy with my decision until Van's can tell me why a tight AN fitting can come loose. If they can, then they should also tell the FAA, so they can place an AD on every AN fitting ever made.

Now in saying this, if you have not completed your kit and don't have gas in your tank, I would do the mod. If you have a QB and don't remember tightening your AN nuts, then you have a very high risk. Unfortunately Van's is not forthcoming with data on QB tubes at this time.

John

Last edited by RV9AFlyer : 03-02-2006 at 06:13 PM.
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  #120  
Old 03-07-2006, 04:56 PM
jstiegel jstiegel is offline
 
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Default fuel tank service bulleten

Builders,
I guess I am missing something. No other AN fitting in the fuel system is safety wired. Also, the AN fittings are, as I understand it, not supposed to have anything on them except an Aluminum to Aluminum fitting. If Van's shipped these fittings in the QB kits un torgued then that is another matter. They should say so. Also, as I understand it, the unfortunate pilot who had an off field landing had warnings that something wasn't right when his tanks got to the level that the AN fitting was uncovered. My son put the floats together so if checking with him that the AN nut was proper tightned I won't do the Service bulletin, as I think it is unnecessary. Tell me where I'm wrong.
John Stiegelmeyer
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