RV-8 fuel starvation accident

[rv6ejguy]

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.

[DanH]

Originally Posted by rv6ejguy

Color coded restrictor fittings are a great idea.

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

Seriously, there is no bandaid for basic competence.

[rv6ejguy]

Originally Posted by DanH

Seriously, there is no bandaid for basic competence.

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

[lr172]

Originally Posted by scsmith

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

[Walt]

Originally Posted by lr172

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.

[BobTurner]

If nothing else, this report should remind pilots that shoulder harnesses really do work - but not if they’re worn too loosly.

[74-07]

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.

[Walt]

Originally Posted by DanH

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.

Originally Posted by rv6ejguy

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.

[DanH]

Originally Posted by Walt

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.

[Walt]

Originally Posted by DanH

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?