Ragwing Fuel Cap Gasket- Accident-Maker

[GAHorn]

While doing research on a ‘48 Cesna 170 accident report…the cause was determined to be the Airline Transport Pilots’ “inadvertent stall” after departure.

Typical NTSB wording. Why did that ATP pilot stall the airplane? Surely an ATP knows about stalls….

The Real reason….was Engine Failure immediately after takeoff….. I’m guessing he stalled the airplane because he was reluctant to hit the trees.

He hit them anyway… But Why..??

Because he had inadequately addressed the airplane’s on-going water-in-the-fuel cont contamination problem.

He died.

Why was water getting into the tanks..? Because the fuel caps were improperly gasketed with old, crumbling gaskets. (Water in ragwing fuel tanks are a common problem and especially-so with the ‘48 C-170 due to that irregular cap-system.)

After draining the tanks and re-filling them…he “ran the engine on the ground 15 minutes to be sure the carburetor didn’t have water in it”…. (not exactly a definitive repair or testing technique ya’ think?) …. then took off anyway.

The ‘48 C-170 uses different type fuel tanks and different fuel caps than later 170-models. They can be difficult to source. As far back as the beginnings of these Forums (at least two decades) this search has been on-going.

Here’s one source: https://www.aircraftspruce.com/catalog/ ... -13766.php

Made of nitrile
OD: 4 1/4” x id 3 1/4”
Thickness: 3/16”

The Real Gaskets company also made them for awhile…out of “silicone” ..which is NOT for gasoline. (I’ve warned previously not to use silicone for gascolator seals because they swell and lose “grip” and fail.)

Real Gaskets now makes them out of “Viton”: https://realgaskets.com/product/fuel-cap-gasket-5/

AND…Both Real Gaskets and Aircraft Spruce are Supporters of TIC170A.

[n2582d]

George,
Can you provide a link or an NTSB accident number for that accident? I couldn’t find it in their database.

I do like the idea of using Viton for fuel cap gaskets. I see that Real Gaskets also makes a set of Viton gaskets for the later model 170 tanks and caps; RG150-FTK. Not as affordable as using Bruce’s templates. Also, at the risk of offending one of our sponsors, I see that they only include one fuel tank adapter gasket, p/n 0523532. It’s the middle gasket in the photo below. There needs to be one inside the tank and an additional one outside the tank — sandwiching the top tank skin. Finally, it appears they do not have a PMA to make these gaskets. Not sure how they can market them for Cessna aircraft without a PMA.

[voorheesh]

The advice on protecting fuel caps from contamination is appreciated.

As a former accident investigator, I want to mention that the NTSB does not establish the “cause” of an accident. They cite “probable cause”, a legally based term with quite a different meaning. The simplest word to describe “probable” is “likely”. Neither does the NTSB assign blame. The sole mission in accident investigation is to find probable cause of transportation accidents with the goal of learning and preventing future occurrence.

Since there is no link to the NTSB report you write of, I assume that reference to an inadvertent stall is based on factual evidence that it occurred prior to impacting trees after takeoff. This would be distinct from a controlled forced landing if the pilot maintained control as he descended/failed to climb following engine failure. In either case, the engine failure is an important, but contributing factor in the accident. An engine failure does not always result in an accident. Accident investigators are usually able to verify the occurrence of a stall based on factual evidence such as damage and impact signatures. Stalls a frequently cited as probable cause based on evidence. Engine failure is harder to ascertain. It’s not unusual for an engine that lost power prior to an accident to display no failure indication in subsequent tear down or testing.

I investigated an accident involving impact with large trees following a fuel starvation related engine failure resulting from a pilot attempting to reach an airport with lower fuel prices than his home base. Fortunately, he survived and provided honest and helpful information. The thing that stood out to me was his description of approaching those large Douglas Fir trees, knowing what was going to happen in mere seconds. He related an almost irresistible urge/reflex to pull up and avoid impact (that would have resulted in a stall). He had to fight it, then likely saved his life by flying (controlling) his airplane into the inevitable crash. I think that element is as important a lesson to pilots as preventing engine failure beforehand.

Reading aviation publications, I still sense, particularly among more experienced pilots, a belief that the NTSB and FAA seek to blame someone or something after an accident. It’s not supposed to be that way. I also frequently hear criticism from pilots that the investigators “don’t know the airplane” or miss what actually happened. Aviation accident investigation is somewhat generic because the process covers so many different aircraft types. Type specific information is always considered. For example, an internet search will reveal helpful information on preventing water ingress in single engine Cessna fuel tanks, much of it emanating from accident reports. Investigators are taught to avoid speculation and biases formed in their own personal experiences. The findings are supposed to be factual and used for initiating safety recommendations and providing preventive information to other users. Overall, I think the NTSB does a good job and represents value for our aviation community.

Thanks George for bringing these stories up on this forum.

[GAHorn]

Voorhees….technically…Yes…NTSB. “softens” their word by using the adjective “probable” when opining on the “cause” of accidents. But, We know what that means. Certainly no one can look into an accident and know Everything that happened 1) to the airplane or 2) to the pilot or 3) in the MIND of the pilot…. and NTSB attempts to remain “impartial” …in the inevitiable event of the subsequent Lawsuits. NTSB doesn’t want to commit to their “findings” in court. (and we all know that NTSB doesn’t always get it “right”. HIstory has proven that several times over.). But that is not the point of the post.

Gary, I don’t have a “link”, As I relied upon a synopsis in an email which was sent to me by another. In MY effort to bring to ragwing-owners the importance of maintaining their ragwing fuel cap gaskets, I used that email info.

THE POINT of my post is the ‘48 C-170 Fuel Cap Gaskets which can allow water-contamination….. not any particular NTSB Investigation.

However…. searching for the possible source of the story…I did find a similar one (with some details which differ slightly)… The NTSB Investigation I found (don’t know if it is the one used by a Member who wanted to bring my attention the importance of the gaskets) under the NTSB Investigation ERA12LA440, Dated 8/13/2013, in which the “Probable Cause” was stated to be “A total loss of engine power due to water contamination of the fuel, the pilot/owner’s inadequate preflight inspection of his airplane, and his failure to maintain airplane control after the engine failure.”

Bottom Line: If you are a 48’ C170 owner…. consider inspecting and maintaining your fuel cap gaskets.

[voorheesh]

The adjective “probable” as used by the NTSB is not to soften their finding of cause. It is a legal requirement (finding Probable Cause in the course of an accident investigation) of the law passed by Congress that allows the NTSB to exist.

The NTSB is not so much impartial as they are objective. That is the term which, in my experience would most apply to the proper conduct of an aviation accident investigation.

NTSB findings of probable cause are inadmissible as evidence in any civil lawsuit brought in the United States. Facts that are contained in NTSB investigations are admissible in those proceedings. Those facts are subject to challenge in court as is the case for any evidence.

Of course the NTSB doesn’t always get it right. Neither do pilots nor others engaged in transportation. But I think we can agree on the value of an independent agency tasked with investigating aviation mishaps and striving to promote safety in our common endeavors. In that regard, our country’s NTSB is second to none.

[GAHorn]

. …The … .NTSB findings of probable cause are inadmissible as evidence in any civil lawsuit brought in the United States. Facts that are contained in NTSB investigations are admissible in those proceedings. Those facts are subject to challenge in court as is the case for any evidence.
…
Of course the NTSB doesn’t always get it right.

That “inadmissible” and “legally based term” is what I referred when I used the “soften” word. NTSB not only doesn’t “always get it right”…they also sometimes refuse to re-open investigations despite convincing evidence they got it Wrong. (The 172 crash NTSB attributed to a fuel selector valve (The 170 News, Jan, 2011)and the NTSB predecessor CAB also used the “probable cause” phraseology. The TWA crash in the Sandias between ABQ and SAF when CAB’s “probable cause” was pilots suicide-pact is one that comes to mind.)

But THIS problem isn’t NTSB or CAB…It’s ‘48 C—170 fuel cap gaskets.

(If this thread becomes focussed on accident investigations instead, perhaps we should split the Topic.)

[voorheesh]

No need to discuss NTSB any further, George unless others chime in. Thanks again for addressing safety issues.

[GAHorn]

Here’s another accident attributed to the ‘48 C-170 (and others) proclivity for water contamination:

https://www.accidents.app/summaries/acc ... 0711X34759


And another:

https://www.accidents.app/summaries/acc ... 0615X01834

And another: (old mogas and water, but the wings/tanks were removed before NTSB could determine Probable Cause “ A total loss of engine power for reasons that could not be determined based on the available evidence.”

https://www.accidents.app/summaries/acc ... 1127X35837

While ‘48 “ragwings” are particularly susceptible, they are not alone…. Here’s a B-model: (Note, this was fresh annual mx flight. Did YOUR carb bowl drain plug get opened and carb bowl drained last annual? I believe It’s often overlooked.)


https://www.accidents.app/summaries/acc ... 0107X20101

Here is link to the NTSB accident database:

https://www.ntsb.gov/Pages/AviationQuery.aspx