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#61
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Bad fuel gauges?
On 2008-02-24 17:29:14 -0800, Jay Maynard
said: On 2008-02-24, wrote: No, I haven't just proclaimed that. Rather, I've explained in detail why I think the gauges ARE useful, in a particular way, if they're anything like the dozens of planes I've rented in various places. And I've explained in detail why I think they're illegal otherwise, citing specific regulations. (There may or may not be a "reality" that illegal planes are common--but that doesn't change whether they're illegal.) And CJ and I and others have given reasons that fuel gauges are desirable for safety as well as legality. You have not, however, explained why, since fuel gauge accuracy is notoriously unreliable for good and sufficient reason, half the GA fleet or more isn't grounded. Your responses are all straight out of the book, with no grounding in the real world. I would have to see some actual evidence that half the GA fleet should be grounded for inaccurate fuel gauges. In fact, I doubt if they are nearly as inaccurate as you claim them to be. Blind belief in an aviation legend is not real world experience. Yes, I know fuel gauges can be inaccurate. But that does not mean that they are always inaccurate, that they are totally unusable, or that they only have to be accurate when they are empty. Assertions like that are simply nonsense. Airplane fuel gauges are generally accurate. Yes, they can be thrown off by lack of maintenance, unusual attitudes, turbulence, and malfunction. But those are the exceptions, not the rule. Flying with malfunctioning fuel gauges can get your ticket pulled, whether you think that is fair or not. Flying with a malfunctioning fuel gauge simply because you think that is normal or that it is inaccurate anyway is simply an excuse for poor piloting, poor maintenance, and general laziness. -- Waddling Eagle World Famous Flight Instructor |
#62
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Bad fuel gauges?
C J Campbell wrote in
news:2008022418524316807-christophercampbell@hotmailcom: On 2008-02-24 17:29:14 -0800, Jay Maynard said: I would have to see some actual evidence that half the GA fleet should be grounded for inaccurate fuel gauges. In fact, I doubt if they are nearly as inaccurate as you claim them to be. Blind belief in an aviation legend is not real world experience. Yes, I know fuel gauges can be inaccurate. But that does not mean that they are always inaccurate, that they are totally unusable, or that they only have to be accurate when they are empty. Assertions like that are simply nonsense. Airplane fuel gauges are generally accurate. Yes, they can be thrown off by lack of maintenance, unusual attitudes, turbulence, and malfunction. But those are the exceptions, not the rule. Flying with malfunctioning fuel gauges can get your ticket pulled, whether you think that is fair or not. Flying with a malfunctioning fuel gauge simply because you think that is normal or that it is inaccurate anyway is simply an excuse for poor piloting, poor maintenance, and general laziness. I'd agree with al of this except the part that says they're generally reliable. I've seen lots of them that aren't. Lots and lots! Bertie |
#63
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Bad fuel gauges?
The requirement for indications of a tank's fuel level (not just on
empty) is stated in 91.205b9, 23.1305a1, and 23.1337b. Let me just quote these. 91.205, b9: "(a) General. Except as provided in paragraphs (c)(3) and (e) of this section, no person may operate a powered civil aircraft with a standard category U.S. airworthiness certificate in any operation described in paragraphs (b) through (f) of this section unless that aircraft contains the instruments and equipment specified in those paragraphs (or FAA- approved equivalents) for that type of operation, and those instruments and items of equipment are in operable condition." .... (9) Fuel gauge indicating the quantity of fuel in each tank. I did my primary training in a plane that had a right wing tank fuel gauge that always showed less than "F" when the tank was completely full. If the interpretation of the FAR is STRICT, I guess that means my training was done illegally, because the gauge DID NOT indicate the quantity of fuel in the right wing tank (ie, FULL). Rather, it indicated less than full. But the writing of the reg is not explicit (they get explicit in 1337b). To me it comes down to ramp checks, FAA enforcement, and case law. I have never flown that aircraft to the end of its usable fuel, so I don't if the aircraft I did my primary training in adheres to 1337b: "(b) Fuel quantity indicator. There must be a means to indicate to the flightcrew members the quantity of usable fuel in each tank during flight. An indicator calibrated in appropriate units and clearly marked to indicate those units must be used. In addition-- (1) Each fuel quantity indicator must be calibrated to read "zero" during level flight when the quantity of fuel remaining in the tank is equal to the unusable fuel supply determined under [Sec. 23.959(a);]" So, what's the case history? How many pilots / mechanics have been fined, had their certification suspended or even revoked because a fuel gauge was shown to not indicate "the quantity of fuel in each tank." The FAA regs listed only speak to calibration when talking about zero useable fuel. Nothing else. If that's the only unambiguous calibration statement in the FARs then I think that's because the FAA realizes fuel gauge accuracy is subject to reasonable limitations. Why would they otherwise have us spend so much time understanding calculated vs real fuel usage, especially during cross country training for the private certificate? If gas gauges were really accurate then the FAA wouldn't bug us so much about learning to calculate and cross-check, and cruise charts wouldn't be such a critical part of the POH. The recommended way and the way we train is to KNOW YOUR AIRCRAFT through repeated measurement and cross- checking the perf charts. No FAA or other training manual says "Just check you gas gauge real quick to see if you need to pull over for gas -- and make sure you land and refuel when the idiot light comes on!" Gas gauges provide solid value as indicators of possible leak situations and when you are almost out (again, calibration is mandated to be correct only at zero). Lawyers specialize in writing that is crystal clear when they want it to be, and subject to court judgement otherwise. I think the fuzzy language the government lawyers used in crafting the regs around fuel gauges was done on purpose. |
#64
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Fuel Quantity Measurement
On Sun, 24 Feb 2008 17:26:53 -0800, RST Engineering wrote:
a) floats inherently leak over time unless they are some light solid, and then they have a tendency over decades to break down and saturate. Kevlar? -- Remove numbers for gmail and for God's sake it ain't "gee" either! |
#65
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Bad fuel gauges?
On Feb 24, 8:29*pm, Jay Maynard
wrote: On 2008-02-24, wrote: You have not, however, explained why, since fuel gauge accuracy is notoriously unreliable for good and sufficient reason, half the GA fleet or more isn't grounded. Yes I've repeatedly explained that. What I keep pointing out is that the gauges are typically at least accurate enough to alert you to a large leak, which is a warning that your flow calculations cannot give you. That makes the gauges useful (and operable), in a limited but important way, and explains why they're required for airworthiness. But as I have acknowledged, the flow calculations are typically much more reliable than the gauges under NORMAL circumstances. That's fine-- the guages are just one part of how you're supposed to keep track of your fuel. |
#66
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Bad fuel gauges?
On Feb 24, 8:06*pm, Clark wrote:
That said, how on Earth can fuel gauges be considered accurate? At the very least one would have to specify attitude (which some gauges do but most don't). Maybe there could be a calibration card for airspeed, weight, and CG? Wouldn't that be fun? The gauges are typically at least accurate enough to alert you to a large leak, which is a warning that your flow calculations cannot give you. That makes the gauges useful (and operable), in a limited but important way, and explains why they're required for airworthiness. As I have acknowledged, the flow calculations are typically much more reliable than the gauges under NORMAL circumstances. That's fine--the gauges are just one part of how you're supposed to keep track of your fuel. |
#67
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Bad fuel gauges?
On Feb 24, 4:10 pm, Bob Noel
wrote: In article , No. Cost is not part of the equation wrt reducing risk, at least as far as the FAA is concerned. If you were an applicant and tried to get an aircraft certified that didn't meet the standards in AC 23.1309 or AC 25.1309 because it would cost too much, the FAA would deny the application. I see what you're getting at. Those ACs indeed specify a maximum acceptable probability for e.g. a catastrophic failure, regardless of the cost of keeping the probability within that bound. But that's still consistent with my point about cost, for three reasons. First, the decision where to set the acceptability threshold is already informed by the FAA's knowledge of what threshold is affordable. The ACs' acceptable probability of catastrophic failure, especially for the less expensive classes of GA aircraft, is high enough to allow many fatalities per year across the fleet. If much higher safety were achievable at a reasonable cost, the FAA would presumably have set the probability threshold lower. Second, for the more expensive classes of GA aircraft, that threshold IS set lower, by two or three orders of magnitude! Presumably, that's in part because the bigger planes can afford to meet higher safety standards--standards that would swamp the cost of the smaller planes. Third, those ACs set a CEILING for acceptable failure probabilities. Unless I've missed something, there's nothing in the ACs to prevent the FAA from deciding that a particular item of safety equipment is required for airworthiness, even if the absence of that equipment would still leave the catastrophe probabilities within the standards set by the ACs. And cost is surely a factor in making THOSE decisions. (For example, if ADS-B technology cost $500,000 per plane, the FAA would not be proposing to require it.) |
#68
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Bad fuel gauges?
wrote in message ... The gauges are typically at least accurate enough to alert you to a large leak, which is a warning that your flow calculations cannot give you. That makes the gauges useful (and operable), in a limited but important way, and explains why they're required for airworthiness. Fuel gauges fail a lot more often than we develop significant leaks, and fuel gauges will never be able to reassure you that you don't have small leak causing an extreme fire hazard. Hence, experience has taught all of us (including the FAA), that there are much better ways to manage your fuel 99 and 44/100% of the time, than the fuel gauges made possible by current technology. Get over it!! I can assure you: if you get caught on a ramp check, and they even notice a failed fuel gauge, and are anal enough to stick you for it, and they can prove that it didn't just happen, It just wasn't your day to be flying, and you are probably damn lucky you didn't actually get in the air. These are the kind of days you get run over by an F-16, loose both mags over water, stroke out, your dog leaves you, etc. You should actually be glad you only got stuck with 90 day suspension for a bad fuel gauge. |
#69
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Bad fuel gauges?
wrote in message ... On Feb 24, 4:10 pm, Bob Noel wrote: In article , No. Cost is not part of the equation wrt reducing risk, at least as far as the FAA is concerned. If you were an applicant and tried to get an aircraft certified that didn't meet the standards in AC 23.1309 or AC 25.1309 because it would cost too much, the FAA would deny the application. I see what you're getting at. Those ACs indeed specify a maximum acceptable probability for e.g. a catastrophic failure, regardless of the cost of keeping the probability within that bound. But that's still consistent with my point about cost, for three reasons. First, the decision where to set the acceptability threshold is already informed by the FAA's knowledge of what threshold is affordable. The ACs' acceptable probability of catastrophic failure, especially for the less expensive classes of GA aircraft, is high enough to allow many fatalities per year across the fleet. If much higher safety were achievable at a reasonable cost, the FAA would presumably have set the probability threshold lower. Second, for the more expensive classes of GA aircraft, that threshold IS set lower, by two or three orders of magnitude! Presumably, that's in part because the bigger planes can afford to meet higher safety standards--standards that would swamp the cost of the smaller planes. Third, those ACs set a CEILING for acceptable failure probabilities. Unless I've missed something, there's nothing in the ACs to prevent the FAA from deciding that a particular item of safety equipment is required for airworthiness, even if the absence of that equipment would still leave the catastrophe probabilities within the standards set by the ACs. And cost is surely a factor in making THOSE decisions. (For example, if ADS-B technology cost $500,000 per plane, the FAA would not be proposing to require it.) Your going to "fit right in" around here! |
#70
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Fuel Quantity Measurement
On Feb 24, 8:26 pm, "RST Engineering" wrote:
Because a) floats inherently leak over time unless they are some light solid, and then they have a tendency over decades to break down and saturate. b) the "state of the art" for float sensors use a wiper against a nichrome wirewound resistor and the wiper tends to wear a hole and the nichrome tends to redistribute itself across the form somewhat nonlinearily. c) just because it was good enough for Henry Ford, it's good enough for us {;-) Good point. I never thought about the leaking float. |
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