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RV-8 fuel starvation accident

The shop obviously did not test for full-power runup and match the fuel flow to what should be consumed - the difference there should have been way obvious during any attempt to calibrate the fuel flow.
 
Some thoughts:

1. The report mentions that the fuel tank root ribs were pulled out of the wing skins. It would be nice to know if the forward attach brackets had the proper slots as depicted on the plans, or simply match-drilled holes? (An example of when it would be good for NTSB examiners to recruit assistance from someone familiar with the aircraft type).

2. Really sad that the fuel supply used a restrictor fitting intended to supply gauges. No mention if that installation was performed by the avionics shop that installed the G3 or if that installation was performed by the owner.

3. The report mentions that the 5-pt harness was intact, yet there were impact marks on the panel. The panel is fairly close to the pilot on the RV-8. But not close enough to allow impact with the panel unless the belts are REALLY loose.
 
They used the restricted fitting which normally is for fuel pressure as the main output to the carb, major oops !
 
Wow. Simply wow. I recently made a change to my fuel system and have had it independently inspected by two sets of knowledgeable eyes in addition to my own. Still, my spidey senses are tingling full strength at the thought of having potentially introduced the same kind of issue as noted in this accident report. Before installing the cowls I'm going to look at the plumbing again, thanks to this timely post.
 
Nothing in the report tells us who plumbed it...

https://data.ntsb.gov/Docket/Document/docBLOB?ID=12468917&FileExtension=pdf&FileName=Photo 1-Rel.pdf

I once caught an engine driven pump plumbed backwards during a TC visit, but the fellow was a first time builder, and it wouldn't have run anyway.

To my knowledge, there is only one shop on the field there that will do panel installs on experimentals. I know the field quite well.

That still doesn't tell us if it was that particular shop that plumbed it, versus the aircraft owner.
 
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Wow. It's interesting to me that the line is capped off. You have to wonder if the fuel pressure gauge was not hooked up at all.
It helps to have a checklist after a panel installation and have another set of eyes look things over, especially when there are so many potential changes in the engine compartment.

Vic
 
Wouldn't a run up have discovered this on the ground?

Probably only a high power run up….most run ups are what say 1700 rpm….then 1000 and a dead cut check….so I’d think no….it was starvation at high power caused by the fitted restriction….
 
Very unfortunate, probably some young A&P who has never worked on an RV and there was no way for him to know that was a special fitting.
Perhaps fittings like that should be identified somehow as ‘non-standard’, maybe painted red?

I’ve seen lots of ‘WTF’ stuff where someone had no clue, so it pays to have your RV work done by a ‘specialist’ who is familiar with the systems we have that are not seen on most GA aircraft. I suspect many RV guys would have caught that mistake.
 
Probably only a high power run up….most run ups are what say 1700 rpm….then 1000 and a dead cut check….so I’d think no….it was starvation at high power caused by the fitted restriction….

I don't think you can make 75ish hp with that size orifice...
 
That's really a sad situation. Its a very basic fuel setup to mess it up so badly. It's a shame to lose a plane and have serious injuries for something like this.
 
would'a - should'a - could'a

After modifying fuel system (adding fuel flow) it would be wise to do a fuel flow test?
sender could be jammed, line could be collapsed, or in this case the totally unexpected wrong fitting.
 
Digging in to the NTSB docket, there are 5 items to VIEW at the lower right. The third is the Maintenance Record 5/24/21. Shows who did the work. Also indicates “Aircraft was Groundrun by the owner to confirm all systems operational”.
 
A short ground run may not have shown it. Someone else should check but I calculated an 0360 at 1800 rpm might only use 3 ounces in a 10 second ground run. The restrictor may have filled the float bowl while it was idling.
 
A short ground run may not have shown it. Someone else should check but I calculated an 0360 at 1800 rpm might only use 3 ounces in a 10 second ground run. The restrictor may have filled the float bowl while it was idling.

Yes, I think that is a likely assumption. It would take a loooooong ground run to empty the float bowl.

Best to disconnect the hose at the carburetor and put it in a bucket. Run the boost pump for 30 seconds or so and measure the volume in the bucket. For a properly functioning system, you should get something like 30 gal/hr or more.
Had they done this, they would have gotten a trickle, and would have known something was wrong.
 
would'a - should'a - could'a

After modifying fuel system (adding fuel flow) it would be wise to do a fuel flow test?
sender could be jammed, line could be collapsed, or in this case the totally unexpected wrong fitting.

Absolutely, I have recommended it several times here , remove at the carb in this case back pressure the outlet and run at 125% of max engine fuel flow with the boost pump.

But, normal mechanics are not wired that way. They always (well 99%) assume that the design is correct and only a part is broken. A prototype mechanic was trained/wired to check everything - like a good builder.
 
After engine or fuel system maintenance, I was taught to do a full power run up for at least 30 seconds. That probably would have emptied the bowl in this case.

Real shame. Shows you can't be too careful checking things. I agree with Bill. Most mechanics would assume things are ok. Color coded restrictor fittings are a great idea.
 
Yes, I think that is a likely assumption. It would take a loooooong ground run to empty the float bowl.

.

You can't empty the bowl and still have a running engine. Once the volume drops in the bowl by as little as 1/16" or so it will start to run pretty lean. By a 1/4" you couldn't help but notice it. If you look at the manuals, float height is set in 64ths of an inch. Hi perf carbs, like a holley, actually have jam nuts and adjusters for fine tuning the height from outside the carb. They are that sensitive. Its all physics in a carb. The height of the top of fuel must be very close to the delta spec'ed for the height of the outlet in the venturi. Off just a hair and the flow rates start changing for any given pressure drop occurring in the venturi. As Bernoulli taught us, the higher the air flow through a constant venturi, the greater the pressure drop. The bowl isn't as deep as it is to provide a reserve, it is as deep as it is to get the fuel top closer to the main outlet to make the physics work.

The real question is how much flow can go through the restrictor compared to the flow needed at the runup RPM. If it was close, the pilot could have run there for a long time and not noticed the issue.

Larry
 
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You can't empty the bowl and still have a running engine. Once the volume drops in the bowl by as little as 1/16" or so it will start to run pretty lean. By a 1/4" you couldn't help but notice it. If you look at the manuals, float height is set in 64ths of an inch. Hi perf carbs, like a holley, actually have jam nuts and adjusters for fine tuning the height from outside the carb. They are that sensitive. Its all physics in a carb. The height of the top of fuel must be very close to the delta spec'ed for the height of the outlet in the venturi. Off just a hair and the flow rates start changing for any given pressure drop occurring in the venturi. As Bernoulli taught us, the higher the air flow through a constant venturi, the greater the pressure drop. The bowl isn't as deep as it is to provide a reserve, it is as deep as it is to get the fuel top closer to the main outlet to make the physics work.

Larry

Not sure I agree with this, quite a few accidents on record that were likely due to carb/vapor lock issues, there is definitely enough fuel in the bowl for a quick run up and get you off the ground, but not for long.
 
If nothing else, this report should remind pilots that shoulder harnesses really do work - but not if they’re worn too loosly.
 
Shortly after bringing our new to us RV-8 home, I completely replaced an automotive fuel boost pump based system with an AirFlow Performance system. As part of that changeout, every fitting and hose from the fuel selector forward was replaced with beautiful stuff from Tom at T&S and of course, Airflow Performance. To be safe, I took the drawings to Kinko and had them blow them up and I taped them to the wall so I could easily see every part #, etc.. I wanted to make absolutely certain everything was correct. Two years later, and after a panel upgrade, it hasn't skipped a beat. Change outs like this are a great time to be paranoid as h#&$$! So sorry to hear of this very unfortunate event.
 

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Yes, it would help us identify those who didn't memorize the color code.

Seriously, there is no bandaid for basic competence.

I think this is a rather short-sighted approach to a potential gotchya. With that attitude every plane crash is obviously because of a stupid pilot.

I agree. Lack of competence and judgement cause most aviation accidents, outside of straight mechanical failures.

The major plane makers figured out a long time ago how to prevent screw ups by making things goof-proof for mechanics.


Thank goodness the FAA/NTSB don't take your approach at just blaming!

NTSB PROCESS
While the exact scope and extent of any specific investigation depends on the nature of the accident being investigated, every NTSB investigation goes through the same general process, which involves:

the initial notification and decision to investigate;
on-site fact gathering;
analysis of facts and determination of probable cause;
acceptance of a final report; and
advocating for the acceptance of safety recommendations arising from the investigation.
 
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I think this is a rather short-sighted approach to a potential gotchya. With that attitude every plane crash is obviously because of a stupid pilot.

Actually, I was thinking about the mechanic ...and I bet this would not have gotten out of your shop.
 
Actually, I was thinking about the mechanic ...and I bet this would not have gotten out of your shop.

That's not the point, from my perspective the mechanic was setup to fail with a non-standard part installed that looked like every other AN fitting he's seen. Somehow, he was supposed to know that RV's use "special" AN fittings?

You think I pull every fitting out of a fuel and oil system when I do an annual to see if it was somehow modified?
I would have suspected that was a restrictor fitting just from my experience on RV's, but how was he supposed to know that?
Maybe he should have looked in the "RV Maintenance Manual", which obviously doesn't exist?
 
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The major plane makers figured out a long time ago how to prevent screw ups by making things goof-proof for mechanics.

Thank goodness the FAA/NTSB don't take your approach at just blaming!

You're saying that maintenance errors don't happen any more? Quite a statement.

Probable cause may lead to blame being assigned. That's the hard reality.
 
That's not the point, from my perspective the mechanic was setup to fail with a non-standard part installed that looked like every other AN fitting he's seen. Somehow, he was supposed to know that RV's use "special" AN fittings?

I'm thinking that the "non-standard" part was the AN *cap* on the output port. Maybe it's just me, but if I saw that, I'd be asking "hey, why's that there?" followed quickly by "Which port is which? Is that right?"

Restrictor fittings are not, AFAIK, some rare, almost-mythological thing.

ETA: I'm curious about something...the flared male portion of the O-ring boss fitting is 3/8", but the tapped hole for the pressure fitting is for a 1/8" NPT-to-flare, right? And the red cube takes 1/4" NPT fittings...so somebody had to do some mixing and matching, using reducers or some fittings that aren't commonly used (AN816-4-4D or something like that?). No?

I'm trying to figure out how this apparently got completely overlooked...
 
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When is the last time you saw an AN4 fitting or hose plumbed in the fuel lines going to the carb of an 0360? Looks like a basic lack of knowledge. I bet the -6 fitting was capped off for convenience. It was a more direct route to the carburetor using the -4 port on the fuel pump fitting. It eliminated a 90 degree fitting.
 
Yes, I think that is a likely assumption. It would take a loooooong ground run to empty the float bowl.

It actually doesn't take too long. Whenever I test fly an airplane that hasn't done a fuel flow test, I run it full power for 30 seconds. Why? On the very first test flight I did for someone in an RV-4 back in the 80's I luckily did that. The engine (carburated) quit about 20 seconds into the run. He had the fuel selector plumbed wrong. Running it probably saved my life, if not the airplane.

Vic
 
Poor workmanship

This is so the reason that I want to and can do most of my work myself on my RV-6A.
In another lifetime I had a C-206 and it seems like every time I HAD work done on it the job was shoddy.
You name the repair area and I'll tell you a story of some screw up
Just had a $36,000.00 Dynon panel built and installed in my RV-6A last fall with an Avionics shop nearby.
Wow what a screwed up mess I was left with. And it took them 4 1/2 weeks to fix all their screw ups. WOW!!!!!!!!
Your luck will surely vary Art
 
You're saying that maintenance errors don't happen any more? Quite a statement.

Not what I said so please don't put words in my mouth, but trust me, if Boeing/Douglas didn't make it near impossible to screw things up there would be many more errors then there are today. They've learned those lessons.

Restrictor fittings are not, AFAIK, some rare, almost-mythological thing.

And the red cube takes 1/4" NPT fittings...so somebody had to do some mixing and matching, using reducers or some fittings that aren't commonly used (AN816-4-4D or something like that?). No?

I'm trying to figure out how this apparently got completely overlooked...

Actually, the AN816-4-4D is the standard fitting for FF xdcr when placed in the -4 line between the servo and divider in an injected system.
 
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So, should we/vans consider much smaller restrictor aperatures? I understand that with air (MP) a restrictor can induce a lag in the reading, but with liquids, how small can you go?
 
Actually, the AN816-4-4D is the standard fitting for FF xdcr when placed in the -4 line between the servo and divider in an injected system.

That's why I said "something like that", because I wasn't sure, it just seemed like it should have triggered some *thinking* about which was which and what was the right fitting and hose to use, and how come one of the two is capped off ("I wonder what THAT'S for").

It didn't seem right to me and now I know why...now at the hangar, I see that my injected (Precision Airmotive) throttle body takes a -6 on the inlet side, and -4 on the outlet side, and I have the FT-60 between the body and the spider. A bit different setup than the accident aircraft (carbureted, FF meter after pump).

Still...
 
A short ground run may not have shown it. Someone else should check but I calculated an 0360 at 1800 rpm might only use 3 ounces in a 10 second ground run. The restrictor may have filled the float bowl while it was idling.

The winner. Exactly.
 
Not that my $.02 counts here, but Steve and I have worked with many builders, owners, mechanics, and me personally 2 occasions the NTSB to answer specific RV related questions. Same for quite a few certified planes. Most all ( not all but the vast majority) all had -6 hoses from the mechanical pump to the carb or servo. On occasion we'd see a -5, but I cant remember ever seeing a -4. The thing that stuck out to me was the 2 different compostion hoses. The hose from the pump to the transducer was an Aeroquip AE666-4 integral firesleeved version. Pretty pricey as compared to the standard teflon version on the carb side.
So in my mind someone doing the install just happen to have a AE466-4 hose to put in there, so they could use the -4 port on the pump tee. Never mind the -6 that was already there and the proper size. Maybe they didnt know they could loosen the lock nut and rotate the tee to a better orientation. Maybe thye just happen to have some fittings in the tool box ( yep these fit, we'll use them) . Thats a question that eventually will get asked.

As for making the restrctor fittings colored RED----we make ours in steel, so I think it might be alittle difficult to do. OH----and we dont use aluminum fittings in that area.

Tom
 
I’m not even sure that there was a restrictor fitting in that erroneously placed line. The NTSB report says that there was a #4 “reduced flow” fitting with the 3/8” (#6) line capped off. Well, a number 4 fitting would be reduced, when #6 is normal. I am not sure an engine can even run, or do a run up on the fuel flow through a #4 line with a restrictor fitting in that line. And even an uninformed mechanic should notice a fitting with a tiny restrictor in it trying to feed a carburetor. A #4 line could feed enough fuel flow for taxi and run up (with no restrictor fitting), but unable to flow 18+ gph at takeoff power.
Everyone can agree that there was oversight in work being done, especially when an obvious need for transition couplers being used when going from a fuel pump (3/8 to 1/4) to FF transducer (back to 3/8) to carburetor. This is not normal. Who knows if this mistake was by a mechanic who didn’t perform his due diligence, or a EXP owner who dictated what he wanted done. Unfortunate outcome unrelated to the intended purpose of the upgrade - new G3X panel.
 
I’m not even sure that there was a restrictor fitting in that erroneously placed line. The NTSB report says that there was a #4 “reduced flow” fitting with the 3/8” (#6) line capped off. Well, a number 4 fitting would be reduced, when #6 is normal. I am not sure an engine can even run, or do a run up on the fuel flow through a #4 line with a restrictor fitting in that line. And even an uninformed mechanic should notice a fitting with a tiny restrictor in it trying to feed a carburetor. A #4 line could feed enough fuel flow for taxi and run up (with no restrictor fitting), but unable to flow 18+ gph at takeoff power.

Figure 3 in the NTSB prelim report shows the fitting in question:
 

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Fuel

That's why nobody but me ever touches my airplane. A proper ground flow test would have identified that immediately.
 
Figure 3 in the NTSB prelim report shows the fitting in question:

Wow Matt. I’m surprised that the flight ever got to the point it did before failure with that fitting. Makes sense though. It took more than 2 minutes for my engine to quit after selecting OFF on my fuel selector with the engine at idle. I guess that restrictor fitting can feed the bowl at a low power setting, and then the filled bowl can support any run up. Then the bowl refills between run up and takeoff and the restrictor fitting can’t support the fuel flow required during a normal climb power setting.
 
Suppose this is a case of the shop hiring the first AP with a pulse and tool box? I don’t think the aviation industry is any different then an auto shop or heavy equipment shop. Pride in craft, experience, and judgement are suffering now. Having built your ship and understanding its systems are necessary for our own safety.

Just a mini rant from Mr. Cynical.
 
Who said the Avionics Shop even had an A&P mechanic? I have seen Avionics Shops that do not have A&P mechanics. That would explain how this could happen. I’ve wondered how they can get by with the work that they do without an A&P.
 
Who said the Avionics Shop even had an A&P mechanic?

https://pbavion.com/

Walt does make a reasonable point about trying to make things foolproof when possible. It's not always possible, but here, perhaps yes.

The common 90 pump outlet fitting is typically tapped 1/8" NPT to provide a fuel pressure port. In this case the trap was set when the builder ran a -4 line to the fuel pressure sender...which is far larger than necessary. So, if you want to avoid setting a zombie trap, install a smaller nipple and hose to the sender...an AN2 or AN3.
.
 

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Who said the Avionics Shop even had an A&P mechanic? I have seen Avionics Shops that do not have A&P mechanics. That would explain how this could happen. I’ve wondered how they can get by with the work that they do without an A&P.

According to the website of the shop that did the work they do have A&Ps with IA and the shop is an FAA certified repair station. I believe they also worked on the fuel tanks at the time of doing the G3X work.

https://data.ntsb.gov/Docket/Docume...sion=pdf&FileName=Mx records_Redacted-Rel.pdf
 
Maybe they should ask.....

Who removed the fuel pressure sender and line that was connected to that restricted fitting?

Was the plane taken to the shop with that restricted fitting capped off?
 
It took more than 2 minutes for my engine to quit after selecting OFF on my fuel selector with the engine at idle.

Many years ago, I was waiting for launch in a Glasflugel H-201 Libelle glider at Waikerie in South Australia while the tow plane was taxiing over to me from the fuel filler.

He sat idling in front of me while I finished my pre-launch checks and accepted the tow rope from the ground crew, then he lined up, tensioned the tow-rope slack, and firewalled the throttle to take off.

Bouncing down the grass runway behind him, I was just starting to get "light" on the main wheel when the tug stopped. It was like he'd applied a hand brake or something.

At the other end of the rope 150 feet behind him, yanking at the tow release knob, I had a fraction of a second to slam full right aileron to jam the wingtip onto the ground to try to turn away from him. There was no way I'd have time to stop; even if the wheel brake was up to the task, there wasn't enough weight on the wheel for it to work anyway.

I ended up rolling to a halt about fifty feet past him, maybe thirty feet off to one side. Replaying it in my mind 15 years later, I feel like I can recall every detail of the interval between tow plane power loss and overtaking it three seconds later.

Near miss. If I'd run into the back of the tow plane at flying speed I'd have written-off two aircraft and my legs.

DR's forum software will *'s any attempts I'd make to describe what I said afterwards. I'm from a culture that uses the C word as a term of endearment, we can say things that'd make half a platoon of Marines all blush at the same time while the other half are standing up to defend their mothers :) You can probably guess about how unimpressed I was.

Anyway: The reason the tug stopped was fuel starvation. The tow pilot had turned off the fuel selector during refueling for some reason, and forgotten to turn it back on again afterwards.

There was enough fuel in the float bowl and the lines for this Piper Pawnee to taxi to my position, idle for long enough for me to get hooked on, and run at full power for long enough for my glider to be starting to leave the ground before the engine stopped, all with no fuel supply at all.

(satellite view: https://goo.gl/maps/hz7PcwyQbMhHyxye9 Refueling is near the SE corner of the big hangar on the western side of the ramp; The glider launch point is the lightish green grass strip just past the kink in the southbound taxiway)

I have no trouble believing that a mis-plumbed O-360 with a restrictor in the fuel line could perform a full high-power run-up without a hiccup. If these engines didn't accept a lot of slack in the system, they'd fail a lot more often. Marginal fuel supply doesn't make them stop, they'll keep running until it runs out completely.


- mark
 
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