I have had experience working with NTSB investigators on several fatal accidents involving Cessna and other airplanes. The NTSB almost always responds to fatal accidents and exercises a standard assignment of "parties" to the investigation. These parties almost always include the aircraft and engine manufacturer and Cessna and Continental employ full time accident investigators who have extensive training and expertise. It has been my experience that Cessna representatives arrive at a scene early on and are invaluable resources in determining factual information concerning the model and serial number (if information is available). For example, investigators carry a portable database or can connect with the manufacturer mainframe, if necessary to determine approved equipment, configurations, etc. They have familiarity with all models from early singles through jets. As parties, they are required to work under supervision of NTSB and I remember the case of a Cessna 150 where the NTSB investigator requested a deputy sheriff be present during a test by a Continental investigator on an engine that took place out in the boondocks and could not be overseen by either the board or FAA. That oversight was documented in the factual report.
These manufacturer representatives obviously have allegiance to their employer but my experience is that they are highly professional and operate under ground rules that provide them with a satisfactory level of independence and objectivity. I can't speak to the investigation that George references in AK but I suspect that the NTSB investigator either received her information from Cessna or at least verified it with their staff. I have never worked with an NTSB investigator who represented themselves as an expert on any aircraft type and I have found each of them to be very open to corrections or updates that occur in an investigation. Good investigators are always open to information provided from reliable sources including type clubs and knowledgable aviators. It is important to remember that accident investigators rely on facts. For example, if a person represents that a fuel shutoff valve functions a certain way, the statement is the fact. The content of the statement must be investigated further and verified. The investigator would look at other factual information to determine how the valve functions and in some cases are unable to arrive at an indisputable answer. In those cases, the fact becomes the inability to discover a definitive answer. It is not unusual to find more than one depiction or explanation concerning the installation of an "O" ring or, for that matter, its purpose. This thread on the configuration of early Cessna 170 fuel systems is a good example of the fact that different models of the same airplane turn up with different set ups. It has been my experience that the Cessna accident investigators would likely note that a 170 either requires or does not require a fuel pump, document the source of their information, and note whether or not the accident aircraft was equipped.
On a final note, the NTSB is an independent organization and its appointed board members are responsible to oversee all activities. If a person has a complaint regarding an action by any NTSB employee, it should be formally presented to the board for review and corrective action. I do not believe that an individual investigator has the power to stop an inquiry or to dismiss potential evidence as George suggests happened. If you study the NTSB mission description, one of its primary functions is to "recommend" fixes based on accident data. Such concerns should be elevated through the NTSB chain of command starting with the Regional Director (they have 4 regions) and if they are not properly addressed should be referred to a congressman or there official who can help find out why. Remember, something that seems thoroughly obvious and indisputable to us, may not be as simple as we imagine when viewed in the bigger scheme of things.
gahorn wrote:It's true the NTSB focused on some small amounts of sediment/water found in the fuel system (quantity and exact locations unknown) but the NTSB investigators, while extremely knowledgeable about airplanes in general, are not intricately familiar with model variations. It is unlikely they would know about the fuel pump problem. Or the fuel tank venting problem. Or the IPC fuel selector valve-assembly incorrect-illustration problem.
(That last example of the fuel selector valve problem was the instigator of an article I wrote for The 170 News on that part. To this day the NTSB lead investigator has refused to re-visit the incorrectness of her written report in which she claimed the fuel flow was blocked because an O-ring was found installed per the incorrect IPC. I guess it's just too much trouble for her because she's already got that one buried. I tried on numerous occasions to point out to her that the incorrect placement of that O-ring will not block the fuel from flowing... it would prevent the valve from shutting completely off!
The official report on that fatal accident remains unchanged because she refuses to reconsider the matter. Her last words on the matter are for US to ask the FAA to issue an AD note and instruct Cessna to revise an obsolete "manual". She never "got it" that the IPC is not an approved document.)
While NTSB accident reports are amazing sources of learning, one of the things I've learned through that exchange with her is that the NTSB is a hard-headed bureaucracy and they sometimes make mistakes they are unwilling to revisit. (The 1950s TWA Convair accident east of ABQ is another example which pops into mind.)
Anyway, the point I'd like to leave with you ragwing guys is: Just because you've gotten away with it for years does not rid you of the problem the factory and certifications engineers knew about when they designed and approved the fuel system. Install that pump and check-valve!
George, we hear you loud and clear
I'm a certified investigator and appreciate your opinion and have personally done over 100 accident investigations. We respect your opinion on this. In the real world the issue may effect perhaps only one or two people. I am one, As I said earlier I'm gathering parts and will reinstall the valve and pumps once overhauled.
Glad to hear that, Poncho.
Harlow, I also respect your words, ...AND the NTSB investigators. I'm aware that airframe and engine mfr's send reps to the accident investigation.
But perhaps you didn't notice that in THIS very special subject... the Cessna Single Engine Fuel Systems Engineer.... was the person who contacted me to inquire as to why the 170 needed a fuel pump and check valve.
The "old timers" are gone at Cessna. The person they send to the accident may not know about fuel pumps and check valves if their own engineering department doesn't.
It was a group of three FAA inspectors at OKC who are partners in a ragwing who contacted me to inquire as to how they might obtain a copy of the STC which allows "installation of an electric pump" ....since their airplane had an undocumented one in it's history....but no pump at all since they've owned it.
Again, not Cessna, not fuel system engineer, not FAA inspector knew the story about these pumps, and the NTSB failed to return my calls, letters and emails until I was finally able to contact the lead investigator MONTHS after many attempts in an effort to provoke interest at NTSB in the clear error of their probable cause of a fatal accident.
Just sayin'....
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention. An originality nut (mostly) for the right reasons.
Aryana wrote:Page 51 in the attached advisory circular outlines one method to test for proper fuel flow against FAR 23.955. I find ACs to be much more valuable instead of reading CFRs. Note that the info in the AC doesn't allow for any exemptions to type certificate requirements.
How does this effect the reason the 48 has a fuel pump? the FARs were not in effect in 1948.
With respect to the original question, my '48 also will sometimes hold fuel pressure indefinitely after shutdown. I always assumed that this is a good indication that the carb needle valve is in pretty good shape, and that the plumbing in that area has no leaks.
With respect to operation without the fuel pump: Successful operation without the fuel pump for awhile (even years) is not sufficient to convince me that it is OK to remove it. If you ever un-cover the pickup point in the fuel tank when low on fuel, you will probably find that flow cannot be re-established without a pump to provide suction.
Will you ever un-cover the fuel pick-up when low on fuel? Probably not, but that is not a chance I want to take, when it really is not that much trouble to keep the fuel system intact and functional.
Aryana wrote:Those FARs would be applicable today if you wanted to get a field approval to deviate from the type certificate. The AC outlines how to gather data for compliance with the current regs.
The expense of gaining the data required to change the fuel system will be more than it is worth.
If --IF I were to attempt to do this I would change the entire fuel system to the "B" model. and do the field approval as an upgrade, IAW the factory blue prints that the data has all ready been proven.
Proving fuel flow on for the AC or the FAR 21 requirements will be the impossible task.
Aryana wrote:You're right, the AC isn't very useful.
I have found that the FAA is much more inclined to approve alterations that are based upon later manufacturers designs such as later models, using blue prints, and manufacturers parts.
one of the questions that is always asked by my PMI at FSDO is a simple one, "has this ever been done before?" When I tell him, yes the manufacturer saw the defect and changed it at serial number XXXXX he will be more inclined to approve it.
No offense to A model owners/drivers out there, but if I were to be in the market for anything other than a B model, it would be a 1948, and the only one I'd really have any interest in is N2500V.
Aryana wrote:
The 48 models are great, and I got to see a couple really nice ones when I was based in San Diego, but I'd probably never buy one when there are so many good B models available.
They are lighter thus have a better useful load, and they are faster. There were only 712 of them built, and are becoming a collectors item. They require no more runway than any of the three models. With the advent of modern covering systems they will set out as well as any aircraft.
Their wings are not lighter, although the lack of later "improvements" and equipment might result in lower empty wts. (And they lack the roll rates of the metal winged versions due to the small 120/140 ailerons.) But I like their classic looks.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention. An originality nut (mostly) for the right reasons.
Aryana wrote:I've flown in close formation with two 48 models, and thought they looked really pretty with the rag wings and double strut. It looks like a well proportioned 120/140 IMO. Neither could out run my B model. Trust me, they tried.
I have mine for a couple of reasons but one is because it was the first model.
Another is my dad started his trucking business in 48.
John
John Hess
Past President 2018-2021 President 2016-2018, TIC170A Vice President 2014-2016, TIC170A Director 2005-2014, TIC170A N3833V Flying for Fun '67 XLH 900 Harley Sportster EAA Chapter 390 Pres since 2006 K3KNT
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