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#2
November 26th 03, 12:16 AM
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#3
November 26th 03, 07:02 PM
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(Michael) wrote in message . com...
(Rich Stowell) wrote Sorry I can't point you to the "harder" data you're looking for, but here's perhaps a little perspective on the issue: According to one NTSB Study, pilots with fewer than either 500 hours total time, or 100 hours in type, are more likely to encounter an inadvertent stall/spin than to have a genuine engine failure (i.e.: a random-event engine failure, not one attributed to such pilot errors as fuel mismanagement). Really? If that were true, then there would be hard data. Yes, really -- see "A Study of Light Plane Stall Avoidance and Suppression." By D.R. Ellis, Report No. FAA-RD-77-25, 1977, p. 6. As for the "hard data" behind this finding, that's for you to follow up on since this is your research project  What the NTSB study REALLY says is that these low time pilots are more likely to encounter an inadvertent stall/spin LEADING TO AN ACCIDENT than to have a genuine engine failure LEADING TO AN ACCIDENT. True, but that's stating the obvious since NTSB only gets involved in, and thus only reports on, those encounters that have led to actual accidents. This is because an engine failure rarely leads to an accident (at least if the ones known to me are any indication) but an inadvertent stall/spin usually leads to an accident. Define "rarely." From an industrial accident prevention standpoint, the theoretical ratio 1:30:300 is often applied wherein for every 331 hazardous encounters of a similar type, only one will progress as far as an actual accident (significant damage and/or injury). The rest fall under "incidents" and "hazards." In other words, typically 1 out of 331 encounters of a similar type results in an accident, whether it's precipitated by an engine failure or an inadvertent stall/spin. In the case of NTSB data, one could extrapolate to get a feel for the order of magnitude of problems pilots deal with in a particular category by multiplying the number of accidents by 331. While it is true that one accident classification may be more prevalent than another (e.g.: more stall/spin fatalities than ground loop fatalities), the ratio of accidents-to-total encounters may very well be equal. In that case, 1 out of 331 would be the same for engine failures leading to accidents as for stall/spins leading to accidents, or any other accident type. I guess one could argue that 1 accident out of every 331 hazardous encounters is "rare" regardless of the cause. In that context, one could then argue that compared to the total number of stall/spin encounters, stall/spin accidents are equally as "rare" as engine failure accidents. For that matter, most engine failure fatalities in light singles are not the result of collision with terrain (which is usually survivable) but of failure to maintain flying speed (which usually isn't). That's basically a stall/spin anyway. Two things: First, approximately 19 percent of stall/spin accidents are preceded by an engine failure. But the primary accident cause is still listed as "stall/spin." See "General Aviation Pilot Stall Awareness Training Study," by William C. Hoffman and Walter M. Hollister, Report No. FAA-RD-77-26, 1976, p. 6. Second, the contention that "failure to maintain flying speed" is "basically a stall/spin anyway" is pure myth. Spins are the result of two ingredients that must coexist: yaw and stall. And neither yaw nor stall is a function of airspeed. Up to the point where the wings decide to bend or break, stalls and spins can and do occur at any airspeed, and in any attitude. For example, stall while at 1-g and Vso and give it some yaw = spin; stall at 1.95 times Vso with +3.8-g's (that's the same as saying "Va and the design limit in the Normal Category") and give it some yaw = spin; give any airplane the right amount of g's at a given airspeed and give it some yaw = spin. In my experience, and based on the research I've read, I'd postulate that the majority of stall/spin accidents occur with the airplane operating somewhere between 1.07 to 1.20 times Vso and 1.15 to 1.41-g. In other words, with pilots pulling into an uncoordinated, accelerated stall while turning at bank angles between 30 and 45 degrees. Rich http://www.richstowell.com
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#4
November 26th 03, 10:48 PM
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#5
November 27th 03, 03:41 AM
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Geez Michael, settle down! So much stress in the cockpit cannot be
conducive to learning or safety... (Michael) wrote in message . com... (Rich Stowell) wrote Really? If that were true, then there would be hard data. Yes, really No, not really. No hard numbers on actual engine failures (or stall-spins for that matter) - only the ones that led to an NTSB reported accident. Interesting that I cited a specific source for my statement, which you summarily ignore as either irrelevant or incapable of leading to numbers that might be relevant to the concerns that started this post. Have you read the study I cited? Have you followed up on the references cited in that study to see where it might lead in the quest for hard numbers on this issue? Or is it easier to just tell everyone else that they're idiots rather than trying to make a serious contribution to the discussion? True, but that's stating the obvious since NTSB only gets involved in, and thus only reports on, those encounters that have led to actual accidents. But this hideously skews the picture. The only way the events are comparable is if the probability of an engine failure leading to an accident is approximately equivalent to the probability of a stall-spin leading to an accident. This is exactly what I am disputing. If it "hideously skews the picture" wouldn't that apply to all accident numbers from NTSB? Each stall/spin accident represent the tip of the stall/spin problem. Each engine failure accident represents the tip of the engine failure scenario. Accident stats are a poor measure of our overall stall/spin awareness, and of our ability to cope with engine failures precisely because accident numbers represent the relatively few pilots who have had an accident. But useful information can be gleaned. Insight into the broader problems might be found as well. And yes, some kind of logical extrapolation may then be possible to assess the overall magnitude of the issue. Define "rarely." From an industrial accident prevention standpoint, the theoretical ratio 1:30:300 is often applied wherein for every 331 hazardous encounters of a similar type, only one will progress as far as an actual accident (significant damage and/or injury). The rest fall under "incidents" and "hazards." That ratio is nothing more than an expression of ignorance. In reality, depnding on the hazard the numbers can be very different. You neglected to define "rarely." And which "numbers" can be very different -- total numbers, ratios, what? Granted, total raw numbers can be significantly different between different accident types, but--as the study of industrial accident prevention postulates--they may be linked by comparable ratios or some other normalizing parameter. Industrial safety types love to quote statistics like this to scare people, but in reality there is usually a reason why some hazardous encounters lead to accidents or incidents while most do not. It's not random. These reasons generally have to do with individual skill, knowledge, and experience as well as factors the industrial safety people are never told because they involve routine violations of safety rules. Often the same dynamic plays out in NTSB investigations. The intent was not to scare anyone, but to try to add some perspective tying the comparatively rare accident to the unknown (perhaps unknowable) number of hazardous situations that are dealt with without further incident. And yes, there are always reasons why aviation accidents happen, be it attributable to Software (checklists, SOP's, etc.), Hardware (airplane, systems, cockpit layout, etc.), Liveware (the pilot, pax, ATC, etc.), Environment, or the interaction of some or all of these. In other words, typically 1 out of 331 encounters of a similar type results in an accident, whether it's precipitated by an engine failure or an inadvertent stall/spin. No, this is total nonsense because stall-spins and engine failures are not similar. First of all, a mechanical failure generally occurs in a manner that is beyond the pilot's control. When the main seal blows out, or the engine swallows a valve, or a rod goes through a cylinder, or the fuel injectors clog with rust - that's almost always completely independent of pilot skill, knowledge, and judgment. On the other hand, an inadvertent stall-spin is caused by the pilot. Therefore, we're not even looking at the same population. OK, Michael knows best, everyone else is an idiot. The point of the pyramidal accident ratio is not to compare engine failures with stall/spins. Yes, they are two dissimilar accident types in terms of the driving mechanisms -- the engine in one case vs. the pilot in the other. But that does not preclude the mix of accidents, hazards, and incidents within each population from sharing a common relationship. From that standpoint, so what if a hole is blown through the crankcase and the windscreen gets covered with oil, obscuring the pilot's ability to see well enough to land under control. The airplane still gets busted and it's still labelled an engine failure accident. Likewise, so what if the pilot skids a turn and causes the airplane to spin into the ground. It's still a stall/spin accident. But for each one of those accidents, there are many more pilots who, with an oil-slicked windscreen, were able to land under control; there are many more pilots who recognized the developing skid, corrected it, and continued under control. The industrial accident maxim only attempts to quantify how many within each group were able to avert the accident. You can disagree with the theory or its application (in which case, it would be beneficial to put forth an alternative), but can't you do it without denigrating? This is supposed to be a forum for learning -- is this how you treat your students? Just by virtue of the fact that the pilot allowed the inadvertent stall-spin situation to develop, we can expect that he is less likely to handle it properly. The same is not true of engine failure. I would disagree thusly: the pilot who does not routinely ("routinely" meaning at least 50% of the time) simulate an engine failure followed by a glide to landing (even from abeam the numbers would be beneficial) is equally as likely not to be able to handle an engine failure to a successful landing (i.e.: no accident) as a pilot who allows the development of an inadvertent stall/spin. I would postulate that the majority of active pilots (except maybe for students) practice simulated engine outs far less than 50% of the time. In the case of NTSB data, one could extrapolate to get a feel for the order of magnitude of problems pilots deal with in a particular category by multiplying the number of accidents by 331. This is absolutely ridiculous. In addition to the issue of hazard exposure (mechanical engine failures don't discriminate but stall-spins do) there is also the issue of hazard magnitude. Off field landings in gliders, for example, are VERY rarely fatal. The ratio there is 5000:1. On the other hand, I would be amazed if the fatality ratio for midairs was much better than 3:1. 331 may be a good all-around average in aviation (or it may not - data are not available) but to apply it indiscriminately to all types of hazards makes no sense at all. Be gentle, you're dealing with an idiot after all Please explainhow an engine failure does not discriminate, yet stall/spin accidents do. The typical stall/spin profile involves a typical pilot on a typical flight -- sounds pretty indiscriminate to me. Please cite your source for the 5000:1 ratio for gliders. Also, glider pilots are always performing engine-out landings, so it would seem to make sense that they'd be better at it than those of us who fly powered airplanes. As for mid-airs, during the period 1977-1986, 40 percent of the mid-airs ended without injury. As for fatality ratio -- yes, the fatality rates between accident types is not at all equal. But for the purposes of counting accidents, a situation in which the pilot walks away unhurt, but the airplane's wing is torn off, is still an "accident" and is therefore equivalent to a case where a pilot lands in a field with the only damage being a tree branch through the windscreen, which kills the pilot. They are both accidents per the definition of the term. For that matter, most engine failure fatalities in light singles are not the result of collision with terrain (which is usually survivable) but of failure to maintain flying speed (which usually isn't). That's basically a stall/spin anyway. Two things: First, approximately 19 percent of stall/spin accidents are preceded by an engine failure. But the primary accident cause is still listed as "stall/spin." There is one school of thought that considers this proper. Just because engine power is lost is no excuse to stall and spin. Gliders don't even have engines. However, that doesn't change the fact that had the engine kept running, the stall-spin would likely not have happened. Second, the contention that "failure to maintain flying speed" is "basically a stall/spin anyway" is pure myth. Spins are the result of two ingredients that must coexist: yaw and stall. And neither yaw nor stall is a function of airspeed. Up to the point where the wings decide to bend or break, stalls and spins can and do occur at any airspeed, and in any attitude. That's all great, but the reality is that in normal flight (not involving aerobatics or other abrupt maneuvering) stall avoidance is all about keeping your airspeed up. Those 19% of stall-spins caused by engine failure are the result of trying to stretch the glide or maneuvering to make a landing area, and likely both. In my experience, and based on the research I've read, I'd postulate that the majority of stall/spin accidents occur with the airplane operating somewhere between 1.07 to 1.20 times Vso and 1.15 to 1.41-g. In other words, with pilots pulling into an uncoordinated, accelerated stall while turning at bank angles between 30 and 45 degrees. That's great, but had those pilots maintained at least 1.3 Vso for these maneuvers, they would not have stalled. Thus saying airspeed is irrelevant is technically correct but not particularly useful. Yes, you can stall at any airspeed in any attitude. I've stalled at 100+ kts (in a plane which normally stalled at 60 kts), full power, and the nose 80 degrees below the horizon - as an aerobatic instructor I'm sure you know exactly what I did wrong to make that happen. That doesn't change the reality - in an engine-out situation, the stall-spin is caused by a failure to maintain flying speed. No -- the stall/spin is caused by yaw and stall, period. Don't yaw and the airplane will not spin, regardless of speed. Be aware of the relationship between g-load and airspeed trend and accidental stalls are less likely. Continuing to tell pilots to fly faster, in order to "maintain flyng speed," unneccessarily makes a lot of perfectly good runways either inaccessible or dangerous to too many pilots. I've seen only two stall/spin accidents here at my 2500-foot home airport over the years, but I've seen many more airplanes broken because they over-ran the runway flying fast enough to "maintain flying speed." As educators, we can do better than that... Rich http://www.richstowell.com
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#6
December 1st 03, 10:25 PM
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#7
December 2nd 03, 06:14 PM
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Michael,
Your experience vis-a-vis how NTSB accident numbers (reported) stack up compared to the actual total number of accidents (reported + unreported) is not at all unusual. I too know of numerous unreported accidents. But this isn't peculiar to aviation -- it probably happens in a lot of different settings and more often than we realize. That's what makes estimating and/or extrapolating accident information so difficult. Perhaps if we always stated a number plus-or-minus some estimate of the error that'd be satisfactory? Again, my intent was to try to establish some kind of broader context for the numbers, imprecise as they may be, unknowable as they may be. Regarding the accident pyramid applied to aviation, see Diehl, Alan E. "Human Performance and Systems Safety Considerations in Aviation Mishaps," The International Journal of Aviation Psychology, vol. 1, no. 2, pp. 97-106; see also Veillette, Patrick R., "Not All Spins Are Equal," University of Utah, 1986 (notes from a presentation). "Relatively few" is the 1 accident per 331 (or X) total hazardous encounters. (Michael) wrote in message . com... I would disagree thusly: the pilot who does not routinely ("routinely" meaning at least 50% of the time) simulate an engine failure followed by a glide to landing (even from abeam the numbers would be beneficial) is equally as likely not to be able to handle an engine failure to a successful landing (i.e.: no accident) as a pilot who allows the development of an inadvertent stall/spin. See, this is another example of a hypothesis (I would not even consider it a theory) that won't stand the light of day. Where did you come up with 50%? Are you suggesting that a pilot who only makes 20 landings a year (hardly unusual, given how little most private pilots fly), of which 10 are simulated engine failures, will do better with a real engine failure than a pilot who makes 300 landings a year, of which only 30 are simulated engine failures? It only makes sense that those who don't practice power-off landings are less likely to be able to competently perform them when necessary, but going from that to hard numbers without additional evidence is simply not reasonable. As a flight instructor charged with the task of educating pilots and (hopefully) offering them guidance in terms of how often to practice certain procedures/maneuvers on their own, what frequency do you recommend in this regard, and on what is that recommendation based? My suggestion to practice gliding approaches to landing on the order of 50% of the time is based on my anecdotal experience flying with licensed pilots in the EMT Program, including performing 14,000+ landings, the great majority of which have been gliding approaches in many types of light airplanes. I think we'd agree that the number of such practice approaches is somewhere between 0 percent of the time (airline-type flying) and 100 percent of the time (gliders). Also, and though it hasn't been stated explicitly, I'm talking in terms of the "average," "typical," "normal" pilot flying the typical light airplane on a typical flight. That said, I do believe that an average pilot who performs 10 gliding approaches out of the 20 approaches annually will be likely to react appropriately to an engine failure. Now, because this pilot may lack the breadth of experience of your atypical 300-landings-per-year pilot who practices gliding 10 percent of the time, the less-experienced pilot (but who is more representative of the norm) may not be as precise overall, yet the fundamental skill set needed to cope should be there nonetheless. In fact, typical pilots under duress will invariably only be able to perform as well as their most basic skill set allows. And those skills that are the most practiced, the most familiar, the most "natural" to the pilot are the ones that will largely determine the outcome. Again, this is based on my anecdotal experience instructing 1,000's of pilots while they are placed under duress during emergency maneuver training -- typical pilots from across the country who are representative "products" of our national flight training system. Also based on my experience, the dominant experience and instincts of the 300-landings-per-year pilot who practices glides 10 percent of the time are not those consistent with gliding, but are those consistent with powered approaches. Such a pilot may actually have to fight harder against the natural urges/tendencies developed and reinforced during all those powered approaches. I don't believe a stall-spin involves a typical pilot at all. The numbers and the anecdotal experience of professional spin/aerobatic flight instructors are totally at odds with your belief. The typical pilot is trained by the typical flight instructor, who himself/herself has a marginal understanding of, and marginal practical experience with, anything related to stalls and spins and therefore, is incapable of adequately providing stall/spin awareness training to their students. See "Re-Examination of Stall/Spin Prevention Training," Transportation Research Record, No. 1379, National Research Council, Transportation Research Board, 1993, by Patrick Veillette. Anecdotally, I see it firsthand every day either flying with, or providing stall/spin seminars to, typical pilots from all around the country -- again, they are representative products of our national flight training system. Moreover, the statistics in every way point to typically-trained pilots on typical flights: NTSB's special study covering the years 1967-69 showed that 1/3 of stall/spin accidents involved pilots with more than 1,000 hours of flight time. The median pilot experience of those involved in stall/spins was 400 hours. Though even higher time pilots succumb to stall/spin accidents, we can profile who is most at risk of an accidental stall/spin as follows: it's the pilot who has logged fewer than 1,000 hours; who is on a daytime pleasure flight in good weather; who is in the traffic pattern; and who is either turning or climbing. Leading up to the inadvertent stall/spin, the pilot will be distracted into making a critical error in judgment. Fixation on the unfolding accident will effectively render 1 in 3 pilots deaf to the blaring stall warning horn. And pilots with fewer than either 500 hours total time, or 100 hours in type, are more likely to encounter an inadvertent stall/spin than to have a genuine engine failure. Consider the following 1987 stats as well: the U.S. boasted 699,653 active pilots who collectively logged an estimated 47.9 million flight hours. Amortized, pilots averaged 68 hours each that year (unfortunately, this average had decreased to less than 50 hours per pilot per year during the 1990's). Consider, too, that the average active flying career of a general aviation pilot is estimated to be 17 years. Hence, the typical pilot will accumulate close to 1,200 hours total time. The majority of pilots--students, private pilots, CFIs--remain squarely in the bull's-eye of the stall/spin accident zone throughout their aviation careers. They are the ones encountering accidental stalls and spins, most of which are just hazardous encounters, some of which result in accidents. As for mid-airs, during the period 1977-1986, 40 percent of the mid-airs ended without injury. So my estimate of a minimum 25% fatality rate for midairs (3:1) doesn't sound too far off. Certainly 1:30:300 is not a good fit. Somewhere, somehow the discussion shifted from "total accidents" to "fatal accidents only." The 1:30:300 is all hazardous encounters leading to all accidents, not total accidents vs. fatal accidents vs. some-injury accidents vs. non-injury accidents. Regarding mid-airs, the question would be, "for each mid-air, how many times are airplanes coming close enough to each other to be considered a hazardous encounter (especially when pilots in both airplanes have their heads buried in the cockpit on a clear VFR day)?" Maybe 331 times as many as the total number of mid-airs that resulted in accidents (whether those on board were injured, killed, or not)??? Rich http://www.richstowell.com
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#8
November 27th 03, 03:41 AM
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Geez Michael, settle down! So much stress in the cockpit cannot be
conducive to learning or safety... (Michael) wrote in message . com... (Rich Stowell) wrote Really? If that were true, then there would be hard data. Yes, really No, not really. No hard numbers on actual engine failures (or stall-spins for that matter) - only the ones that led to an NTSB reported accident. Interesting that I cited a specific source for my statement, which you summarily ignore as either irrelevant or incapable of leading to numbers that might be relevant to the concerns that started this post. Have you read the study I cited? Have you followed up on the references cited in that study to see where it might lead in the quest for hard numbers on this issue? Or is it easier to just tell everyone else that they're idiots rather than trying to make a serious contribution to the discussion? True, but that's stating the obvious since NTSB only gets involved in, and thus only reports on, those encounters that have led to actual accidents. But this hideously skews the picture. The only way the events are comparable is if the probability of an engine failure leading to an accident is approximately equivalent to the probability of a stall-spin leading to an accident. This is exactly what I am disputing. If it "hideously skews the picture" wouldn't that apply to all accident numbers from NTSB? Each stall/spin accident represent the tip of the stall/spin problem. Each engine failure accident represents the tip of the engine failure scenario. Accident stats are a poor measure of our overall stall/spin awareness, and of our ability to cope with engine failures precisely because accident numbers represent the relatively few pilots who have had an accident. But useful information can be gleaned. Insight into the broader problems might be found as well. And yes, some kind of logical extrapolation may then be possible to assess the overall magnitude of the issue. Define "rarely." From an industrial accident prevention standpoint, the theoretical ratio 1:30:300 is often applied wherein for every 331 hazardous encounters of a similar type, only one will progress as far as an actual accident (significant damage and/or injury). The rest fall under "incidents" and "hazards." That ratio is nothing more than an expression of ignorance. In reality, depnding on the hazard the numbers can be very different. You neglected to define "rarely." And which "numbers" can be very different -- total numbers, ratios, what? Granted, total raw numbers can be significantly different between different accident types, but--as the study of industrial accident prevention postulates--they may be linked by comparable ratios or some other normalizing parameter. Industrial safety types love to quote statistics like this to scare people, but in reality there is usually a reason why some hazardous encounters lead to accidents or incidents while most do not. It's not random. These reasons generally have to do with individual skill, knowledge, and experience as well as factors the industrial safety people are never told because they involve routine violations of safety rules. Often the same dynamic plays out in NTSB investigations. The intent was not to scare anyone, but to try to add some perspective tying the comparatively rare accident to the unknown (perhaps unknowable) number of hazardous situations that are dealt with without further incident. And yes, there are always reasons why aviation accidents happen, be it attributable to Software (checklists, SOP's, etc.), Hardware (airplane, systems, cockpit layout, etc.), Liveware (the pilot, pax, ATC, etc.), Environment, or the interaction of some or all of these. In other words, typically 1 out of 331 encounters of a similar type results in an accident, whether it's precipitated by an engine failure or an inadvertent stall/spin. No, this is total nonsense because stall-spins and engine failures are not similar. First of all, a mechanical failure generally occurs in a manner that is beyond the pilot's control. When the main seal blows out, or the engine swallows a valve, or a rod goes through a cylinder, or the fuel injectors clog with rust - that's almost always completely independent of pilot skill, knowledge, and judgment. On the other hand, an inadvertent stall-spin is caused by the pilot. Therefore, we're not even looking at the same population. OK, Michael knows best, everyone else is an idiot. The point of the pyramidal accident ratio is not to compare engine failures with stall/spins. Yes, they are two dissimilar accident types in terms of the driving mechanisms -- the engine in one case vs. the pilot in the other. But that does not preclude the mix of accidents, hazards, and incidents within each population from sharing a common relationship. From that standpoint, so what if a hole is blown through the crankcase and the windscreen gets covered with oil, obscuring the pilot's ability to see well enough to land under control. The airplane still gets busted and it's still labelled an engine failure accident. Likewise, so what if the pilot skids a turn and causes the airplane to spin into the ground. It's still a stall/spin accident. But for each one of those accidents, there are many more pilots who, with an oil-slicked windscreen, were able to land under control; there are many more pilots who recognized the developing skid, corrected it, and continued under control. The industrial accident maxim only attempts to quantify how many within each group were able to avert the accident. You can disagree with the theory or its application (in which case, it would be beneficial to put forth an alternative), but can't you do it without denigrating? This is supposed to be a forum for learning -- is this how you treat your students? Just by virtue of the fact that the pilot allowed the inadvertent stall-spin situation to develop, we can expect that he is less likely to handle it properly. The same is not true of engine failure. I would disagree thusly: the pilot who does not routinely ("routinely" meaning at least 50% of the time) simulate an engine failure followed by a glide to landing (even from abeam the numbers would be beneficial) is equally as likely not to be able to handle an engine failure to a successful landing (i.e.: no accident) as a pilot who allows the development of an inadvertent stall/spin. I would postulate that the majority of active pilots (except maybe for students) practice simulated engine outs far less than 50% of the time. In the case of NTSB data, one could extrapolate to get a feel for the order of magnitude of problems pilots deal with in a particular category by multiplying the number of accidents by 331. This is absolutely ridiculous. In addition to the issue of hazard exposure (mechanical engine failures don't discriminate but stall-spins do) there is also the issue of hazard magnitude. Off field landings in gliders, for example, are VERY rarely fatal. The ratio there is 5000:1. On the other hand, I would be amazed if the fatality ratio for midairs was much better than 3:1. 331 may be a good all-around average in aviation (or it may not - data are not available) but to apply it indiscriminately to all types of hazards makes no sense at all. Be gentle, you're dealing with an idiot after all Please explainhow an engine failure does not discriminate, yet stall/spin accidents do. The typical stall/spin profile involves a typical pilot on a typical flight -- sounds pretty indiscriminate to me. Please cite your source for the 5000:1 ratio for gliders. Also, glider pilots are always performing engine-out landings, so it would seem to make sense that they'd be better at it than those of us who fly powered airplanes. As for mid-airs, during the period 1977-1986, 40 percent of the mid-airs ended without injury. As for fatality ratio -- yes, the fatality rates between accident types is not at all equal. But for the purposes of counting accidents, a situation in which the pilot walks away unhurt, but the airplane's wing is torn off, is still an "accident" and is therefore equivalent to a case where a pilot lands in a field with the only damage being a tree branch through the windscreen, which kills the pilot. They are both accidents per the definition of the term. For that matter, most engine failure fatalities in light singles are not the result of collision with terrain (which is usually survivable) but of failure to maintain flying speed (which usually isn't). That's basically a stall/spin anyway. Two things: First, approximately 19 percent of stall/spin accidents are preceded by an engine failure. But the primary accident cause is still listed as "stall/spin." There is one school of thought that considers this proper. Just because engine power is lost is no excuse to stall and spin. Gliders don't even have engines. However, that doesn't change the fact that had the engine kept running, the stall-spin would likely not have happened. Second, the contention that "failure to maintain flying speed" is "basically a stall/spin anyway" is pure myth. Spins are the result of two ingredients that must coexist: yaw and stall. And neither yaw nor stall is a function of airspeed. Up to the point where the wings decide to bend or break, stalls and spins can and do occur at any airspeed, and in any attitude. That's all great, but the reality is that in normal flight (not involving aerobatics or other abrupt maneuvering) stall avoidance is all about keeping your airspeed up. Those 19% of stall-spins caused by engine failure are the result of trying to stretch the glide or maneuvering to make a landing area, and likely both. In my experience, and based on the research I've read, I'd postulate that the majority of stall/spin accidents occur with the airplane operating somewhere between 1.07 to 1.20 times Vso and 1.15 to 1.41-g. In other words, with pilots pulling into an uncoordinated, accelerated stall while turning at bank angles between 30 and 45 degrees. That's great, but had those pilots maintained at least 1.3 Vso for these maneuvers, they would not have stalled. Thus saying airspeed is irrelevant is technically correct but not particularly useful. Yes, you can stall at any airspeed in any attitude. I've stalled at 100+ kts (in a plane which normally stalled at 60 kts), full power, and the nose 80 degrees below the horizon - as an aerobatic instructor I'm sure you know exactly what I did wrong to make that happen. That doesn't change the reality - in an engine-out situation, the stall-spin is caused by a failure to maintain flying speed. No -- the stall/spin is caused by yaw and stall, period. Don't yaw and the airplane will not spin, regardless of speed. Be aware of the relationship between g-load and airspeed trend and accidental stalls are less likely. Continuing to tell pilots to fly faster, in order to "maintain flyng speed," unneccessarily makes a lot of perfectly good runways either inaccessible or dangerous to too many pilots. I've seen only two stall/spin accidents here at my 2500-foot home airport over the years, but I've seen many more airplanes broken because they over-ran the runway flying fast enough to "maintain flying speed." As educators, we can do better than that... Rich http://www.richstowell.com
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#9
November 26th 03, 06:36 PM
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Rich
Some other data to put in the pot. The Air Force paid some one (Rand Corporation or some other think tank) to do a study on accidents vs flying time. It basically came out that there were two spikes, one around 500 hours and the other around 1000 hours. The 500 hour accidents were attributed to cocky over confidence. Not sure right now what the 1000 spike was but it was caused by something we could train around or change procedures, etc. to reduce as I recall. Big John On 25 Nov 2003 07:57:26 -0800, (Rich Stowell) wrote: Sorry I can't point you to the "harder" data you're looking for, but here's perhaps a little perspective on the issue: According to one NTSB Study, pilots with fewer than either 500 hours total time, or 100 hours in type, are more likely to encounter an inadvertent stall/spin than to have a genuine engine failure (i.e.: a random-event engine failure, not one attributed to such pilot errors as fuel mismanagement). In my case, over 6,400 hours with 5,600+ hours of instruction given (mostly doing spin, emergency maneuver, aerobatic, and tailwheel training -- the type of flying that might be considered harder on an engine than more routine types of flying), I've had several non-critical engine anomalies that were successfully dealt with, including: Prop stoppages during spins due to a couple of students hanging on so tight to the throttle that it choked off the engine -- we call that "fright idle"; Clogged fuel injectors during take-off that only revealed themselves at full throttle; Primer controls that were not truly "in and locked" which has lead to prop stoppages during idle power landings. In addition, two legitimate engine failures as follows: The first, a fuel injector failure as we entered the traffic pattern (after practicing off field landings, no less!) -- landed without further incident; The second, carb ice in a Champ during a flight review choked off the engine during a touch and go -- touched down on the taxiway abeam the departure end of the runway, hit a parked Porshe, bent the airplane, walked away without so much as a scratch. Rich http://www.richstowell.com (Captain Wubba) wrote in message . com... Indeed. Interesting. But I'd still like to see some hard data. This is the kind of problem I run into...most of your pilot friends report that they have had a failure, but the majority of mine report none. And none of the 2000+ hour CFI types I asked (I asked 4 of them) have ever experienced an engine failure. My dad was a pilot with well over 12,000 hours and never had one. Another relative had fewer than 500 hours total in his flying carrer and lost one on his first solo XC. I asked another A&P I ran into at the airport tonight, and he said he thought it should be at least 40,000 hours per in-flight engine failure, but really wasn't sure. Since a big part of flying is risk management, it would be very helpful to *really* know the risks involved. If the odds of losing an engine are 1 in 50,000 hours, then night/hard-IFR single-engine flying becomes a great deal more appealing than if it is 1 in 10,000 hours. I'll try to go over the NTSB data more thoroughly, I think a reasonable extrapolation would be that at least 1 in 4 in-flight engine failures (probably more) would end up in the NTSB database. But the cursory review I made earlier made me think the numbers were much less negative than I had considered before. And the opinions of these A&Ps are very interesting, because while failure might not require a total overhaul, it will require *something* to be done by a mechanic...and if these guys are seeing 30-40 engines make it to TBO for every one needing repair due to an in-flight failure, that might well support the 40,000 to 50,000 hour hypothesis. Cheers, Cap (Michael) wrote in message om... (Captain Wubba) wrote Howdy. I was discussing with a friend of mine my concerns about flying single-engine planes at night or in hard IFR, due to the possibility of engine failure. My buddy is a CFI/CFII/ATP as well as an A&P, about 3500 hours, and been around airplanes for a long time, so I tend to give credence to his experiences. He asked me how often I thought a piston engine had an in-flight engine failure. I guestimated once every 10,000 hours or so. He said that was *dramatically* over-estimating the failure rate. He said that in his experience it is at least 40,000 to 50,000 hours per in-flight engine failure. The only vaguely official number that I've ever seen came from a UK accident report for a US-built twin. The UK investigators queried the FAA on engine failure rates for the relevant engine, and the only answer they got was that piston engines have failure rates on the order of 1 in 1000 to 1 in 10000 hours. This is consistent with my experience. I've had one non-fuel-related engine failure (partial, but engine could only produce 20-30% power) in 1600+ hrs. Most people I know with over 1500 GA hours have had an engine failure. 50,000 hours is not realistic. Excluding a few airline pilots (who have ALL had engine failures) all my pilot friends together don't have 50,000 hours, and quite a few of them have had engine failures. I've heard the maintenance shop thing before, but you need to realize that most engine failures do not result in a major overhaul. Stuck valves and cracked jugs mean that only a single jug is replaced; failure of the carb or fuel injection system (my problem) affects only that component. And oil loss will often seize an engine and make it not worth overhauling. There are no real stats on engine failures because engine manufacturers and the FAA don't want those stats to exist. The FAA could create those stats simply by requiring pilots to report engine failures for other than fuel exhaustion/contamination reasons, but will not. The truth is, FAA certification requirements have frozen aircraft piston engines in the past, and now they're less reliable than automotive engines (not to mention ridiculously expensive). Michael
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November 27th 03, 12:43 AM
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Thanks for that, Big John,
I recall seeing similar stats -- I'll have to dig around in my files to find the context and the reason for that second spike at 1,000 hours ... so much to do! I posted a follow-up to Michaels response to my post as well. Rich http://www.richstowell.com Big John wrote in message . .. Rich Some other data to put in the pot. The Air Force paid some one (Rand Corporation or some other think tank) to do a study on accidents vs flying time. It basically came out that there were two spikes, one around 500 hours and the other around 1000 hours. The 500 hour accidents were attributed to cocky over confidence. Not sure right now what the 1000 spike was but it was caused by something we could train around or change procedures, etc. to reduce as I recall. Big John On 25 Nov 2003 07:57:26 -0800, (Rich Stowell) wrote: Sorry I can't point you to the "harder" data you're looking for, but here's perhaps a little perspective on the issue: According to one NTSB Study, pilots with fewer than either 500 hours total time, or 100 hours in type, are more likely to encounter an inadvertent stall/spin than to have a genuine engine failure (i.e.: a random-event engine failure, not one attributed to such pilot errors as fuel mismanagement). In my case, over 6,400 hours with 5,600+ hours of instruction given (mostly doing spin, emergency maneuver, aerobatic, and tailwheel training -- the type of flying that might be considered harder on an engine than more routine types of flying), I've had several non-critical engine anomalies that were successfully dealt with, including: Prop stoppages during spins due to a couple of students hanging on so tight to the throttle that it choked off the engine -- we call that "fright idle"; Clogged fuel injectors during take-off that only revealed themselves at full throttle; Primer controls that were not truly "in and locked" which has lead to prop stoppages during idle power landings. In addition, two legitimate engine failures as follows: The first, a fuel injector failure as we entered the traffic pattern (after practicing off field landings, no less!) -- landed without further incident; The second, carb ice in a Champ during a flight review choked off the engine during a touch and go -- touched down on the taxiway abeam the departure end of the runway, hit a parked Porshe, bent the airplane, walked away without so much as a scratch. Rich http://www.richstowell.com (Captain Wubba) wrote in message . com... Indeed. Interesting. But I'd still like to see some hard data. This is the kind of problem I run into...most of your pilot friends report that they have had a failure, but the majority of mine report none. And none of the 2000+ hour CFI types I asked (I asked 4 of them) have ever experienced an engine failure. My dad was a pilot with well over 12,000 hours and never had one. Another relative had fewer than 500 hours total in his flying carrer and lost one on his first solo XC. I asked another A&P I ran into at the airport tonight, and he said he thought it should be at least 40,000 hours per in-flight engine failure, but really wasn't sure. Since a big part of flying is risk management, it would be very helpful to *really* know the risks involved. If the odds of losing an engine are 1 in 50,000 hours, then night/hard-IFR single-engine flying becomes a great deal more appealing than if it is 1 in 10,000 hours. I'll try to go over the NTSB data more thoroughly, I think a reasonable extrapolation would be that at least 1 in 4 in-flight engine failures (probably more) would end up in the NTSB database. But the cursory review I made earlier made me think the numbers were much less negative than I had considered before. And the opinions of these A&Ps are very interesting, because while failure might not require a total overhaul, it will require *something* to be done by a mechanic...and if these guys are seeing 30-40 engines make it to TBO for every one needing repair due to an in-flight failure, that might well support the 40,000 to 50,000 hour hypothesis. Cheers, Cap (Michael) wrote in message om... (Captain Wubba) wrote Howdy. I was discussing with a friend of mine my concerns about flying single-engine planes at night or in hard IFR, due to the possibility of engine failure. My buddy is a CFI/CFII/ATP as well as an A&P, about 3500 hours, and been around airplanes for a long time, so I tend to give credence to his experiences. He asked me how often I thought a piston engine had an in-flight engine failure. I guestimated once every 10,000 hours or so. He said that was *dramatically* over-estimating the failure rate. He said that in his experience it is at least 40,000 to 50,000 hours per in-flight engine failure. The only vaguely official number that I've ever seen came from a UK accident report for a US-built twin. The UK investigators queried the FAA on engine failure rates for the relevant engine, and the only answer they got was that piston engines have failure rates on the order of 1 in 1000 to 1 in 10000 hours. This is consistent with my experience. I've had one non-fuel-related engine failure (partial, but engine could only produce 20-30% power) in 1600+ hrs. Most people I know with over 1500 GA hours have had an engine failure. 50,000 hours is not realistic. Excluding a few airline pilots (who have ALL had engine failures) all my pilot friends together don't have 50,000 hours, and quite a few of them have had engine failures. I've heard the maintenance shop thing before, but you need to realize that most engine failures do not result in a major overhaul. Stuck valves and cracked jugs mean that only a single jug is replaced; failure of the carb or fuel injection system (my problem) affects only that component. And oil loss will often seize an engine and make it not worth overhauling. There are no real stats on engine failures because engine manufacturers and the FAA don't want those stats to exist. The FAA could create those stats simply by requiring pilots to report engine failures for other than fuel exhaustion/contamination reasons, but will not. The truth is, FAA certification requirements have frozen aircraft piston engines in the past, and now they're less reliable than automotive engines (not to mention ridiculously expensive). Michael
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