4 ms·

The FAA and Boeing need to investigate this, but you can't make such statistical inferences, since you simply don't have enough data points. There could be no m

The FAA and Boeing need to investigate this, but you can't make such statistical inferences, since you simply don't have enough data points. There could be no more crashes for the next few years with those 350 planes. The FAA and NTSB are very good at what they do, one of the very few examples of government services that work well together with industry, give them some time.

pgreenwood 8y ago
The statistic looks appallingly bad to me viewed as a poisson process. If you had thousands of planes with zero crashes over decades would you consider that as zero data points?
nraynaud 8y ago
You just can't have more data points, because flight travel is too safe. And no, the FAA is not really that good, general aviation pilots die all the time from negligence and the FAA doesn't enforce the rules when pilots violate them (in particular low altitude flying).
- dpe82 8y ago
  General aviation is actually quite safety focused. The entire culture is centered around safety; a large amount of private pilot training time is dedicated to the subject; human factors in particular. Go to any fly-in breakfast and talk to the pilots and inevitably at some point during the conversation you'll hear something about being a safe pilot. That being said, the government gives general aviation pilots a fair amount of freedom once they get their license. There are rules and they are enforced; particularly when violations put the general public at risk. But there's also recognition that it's quite possible to regulate GA out of existence like a lot of other countries have, and that has pretty negative consequences in terms of pilot availability for other purposes. Therefore, regulations scale with the amount of danger the public is exposed to. For example, ultralight aircraft (single place, <254 lbs, <=5gal fuel, <=55kts) are virtually unregulated; the idea being that they're so small and light that they aren't much danger to others. LSA/sport (1-2 place, <=1320lbs, <=120kts) are regulated; require a license and inspections but less stringent than a private license, and so on. Private licenses can't be used for commercial purposes, and generally speaking more training and endorsements or ratings are required for eg. aircraft with multiple engines; those that are >=12,500 lbs, those that land on water, those that have old-school landing gear, etc. etc.
  - nraynaud 8y ago
    When it was time to regulate quadcopters out of existence, we didn't feel the "scaling with the amount of danger the public is exposed to".
- briandear 8y ago
  What’s the “low altitude flying” rule that isn’t being enforced?
  - dlgeek 8y ago
    https://www.law.cornell.edu/cfr/text/14/91.119 https://www.law.cornell.edu/cfr/text/14/91.119 § 91.119 Minimum safe altitudes: General. Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes: (a)Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface. (b)Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft. (c)Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure. (d)Helicopters, powered parachutes, and weight-shift-control aircraft. If the operation is conducted without hazard to persons or property on the surface - (1) A helicopter may be operated at less than the minimums prescribed in paragraph (b) or (c) of this section, provided each person operating the helicopter complies with any routes or altitudes specifically prescribed for helicopters by the FAA; and (2) A powered parachute or weight-shift-control aircraft may be operated at less than the minimums prescribed in paragraph (c) of this section.
  - SomeHacker44 8y ago
    14 CFR 91.119 Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes: (a) Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface.
- hindsightbias 8y ago
  I would liken GA enforcement to be somewhat like motorcyles. Lots of people die on motorcyles and we see bad behavior all the time, but we don't look at law enforcement and say they're doing a bad job. You're simply operating a platform with a higher probability of death than a car or truck when you do screw up.
  - nraynaud 8y ago
    If only model aircraft fliers who for have not killed anyone yet benefited from the same leniency.
kharms 8y ago
We have some idea of a crash rate for safe airplanes. Something like: P(Crash|Miles Flow & Hull Age) If we assume this airplane is safe, we can apply that probability to it and then ask P(2 Crashes|N Miles & 350 New Planes). You would then have a probability for this just being bad luck, and compare that against your prior that this is a safe plane. I haven’t done the math, but my gut says it would point to grounding the plane.
- hexane360 8y ago
  >I haven’t done the math, but my gut says it would point to grounding the plane. "Guts" are notoriously good at statistical inference
- Retric 8y ago
  Depends on your assumptions, but safe aircraft will crash making the first data point meaningless as you are choosing it at the starting point. Second, you are not just running one trial on one design but many trails on many designs. I suggest you try the math as the odds are reasonably high. This changes if you start talking about crashes since the first commercial flight, but those are again different numbers.
- DuskStar 8y ago
  Might also be worth considering P(2 Crashes | N Miles across 350 planes where at least one operator has incompetent maintenance), because that might not be all that different from P(1 crash | N Miles across 350 planes where all operators properly maintain their planes) Look at things like Alaska Airlines Flight 261 [0] - safe airframe, deficient maintenance, plane loses all pitch control and impacts ocean. Yes, this still means that Boeing needs to improve things - single points of failures are never OK on a plane - but it also doesn't (IMO) mean the plane is fundamentally unsafe without those fixes. 0: https://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261 https://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261
- bjourne 8y ago
  According to https://en.wikipedia.org/wiki/Aviation_safety#Evolution https://en.wikipedia.org/wiki/Aviation_safety#Evolution the fatal accidents per million flights were 0.39 in 2018. The MAX8 fleet has been operational for about six months. Assuming 3 flights per day: 350 * 6 * 30 * 3 = 0.189 million flights. To estimate the probability of two accidents, we can use a Poisson distribution with x = 2 and μ = 0.189 * 0.39 = 0.0737 P(x=2) = e^(-μ)μ^x / x! = 0.25% I.e your gut feeling is correct (if my math is correct, that is). If one uses the estimate from a sibling comment of 1 crash in 11 million fights, the probability decreases further to 0.01% Actually the correct calculation is: 1 - P(x=0) - P(x=1) = 0.26% since we are looking for the probability of there being more than one plane crash -- not just the probability of there being exactly two plane crashes.
Scoundreller 8y ago
I think I see a new product from LLoyd’d of London Syndicates: Early big double failure on new airframe insurance. A perfectly good airframe can have its reputation ruined with 2 incidents in a short time period.
objektif 8y ago
If they need time shouldn't the first course of action be grounding this aircraft?
KorematsuFred 8y ago
Better safe than sorry. For example if a plane crashes in the first flight should we just ignore it because it is statistically insignificant ? 2/350 seems like a fairly good number to ground the plane and do an investigation. In general this is good for aviation industry because next time Boeing will not cut corners as it has so far.

pgreenwood 8y ago

The statistic looks appallingly bad to me viewed as a poisson process. If you had thousands of planes with zero crashes over decades would you consider that as zero data points?

nraynaud 8y ago

You just can't have more data points, because flight travel is too safe. And no, the FAA is not really that good, general aviation pilots die all the time from negligence and the FAA doesn't enforce the rules when pilots violate them (in particular low altitude flying).

dpe82 8y ago
General aviation is actually quite safety focused. The entire culture is centered around safety; a large amount of private pilot training time is dedicated to the subject; human factors in particular. Go to any fly-in breakfast and talk to the pilots and inevitably at some point during the conversation you'll hear something about being a safe pilot. That being said, the government gives general aviation pilots a fair amount of freedom once they get their license. There are rules and they are enforced; particularly when violations put the general public at risk. But there's also recognition that it's quite possible to regulate GA out of existence like a lot of other countries have, and that has pretty negative consequences in terms of pilot availability for other purposes. Therefore, regulations scale with the amount of danger the public is exposed to. For example, ultralight aircraft (single place, <254 lbs, <=5gal fuel, <=55kts) are virtually unregulated; the idea being that they're so small and light that they aren't much danger to others. LSA/sport (1-2 place, <=1320lbs, <=120kts) are regulated; require a license and inspections but less stringent than a private license, and so on. Private licenses can't be used for commercial purposes, and generally speaking more training and endorsements or ratings are required for eg. aircraft with multiple engines; those that are >=12,500 lbs, those that land on water, those that have old-school landing gear, etc. etc.
- nraynaud 8y ago
  When it was time to regulate quadcopters out of existence, we didn't feel the "scaling with the amount of danger the public is exposed to".
briandear 8y ago
What’s the “low altitude flying” rule that isn’t being enforced?
- dlgeek 8y ago
  https://www.law.cornell.edu/cfr/text/14/91.119 https://www.law.cornell.edu/cfr/text/14/91.119 § 91.119 Minimum safe altitudes: General. Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes: (a)Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface. (b)Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft. (c)Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure. (d)Helicopters, powered parachutes, and weight-shift-control aircraft. If the operation is conducted without hazard to persons or property on the surface - (1) A helicopter may be operated at less than the minimums prescribed in paragraph (b) or (c) of this section, provided each person operating the helicopter complies with any routes or altitudes specifically prescribed for helicopters by the FAA; and (2) A powered parachute or weight-shift-control aircraft may be operated at less than the minimums prescribed in paragraph (c) of this section.
- SomeHacker44 8y ago
  14 CFR 91.119 Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes: (a) Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface.
hindsightbias 8y ago
I would liken GA enforcement to be somewhat like motorcyles. Lots of people die on motorcyles and we see bad behavior all the time, but we don't look at law enforcement and say they're doing a bad job. You're simply operating a platform with a higher probability of death than a car or truck when you do screw up.
- nraynaud 8y ago
  If only model aircraft fliers who for have not killed anyone yet benefited from the same leniency.

kharms 8y ago

We have some idea of a crash rate for safe airplanes. Something like: P(Crash|Miles Flow & Hull Age) If we assume this airplane is safe, we can apply that probability to it and then ask P(2 Crashes|N Miles & 350 New Planes). You would then have a probability for this just being bad luck, and compare that against your prior that this is a safe plane. I haven’t done the math, but my gut says it would point to grounding the plane.

hexane360 8y ago
>I haven’t done the math, but my gut says it would point to grounding the plane. "Guts" are notoriously good at statistical inference
Retric 8y ago
Depends on your assumptions, but safe aircraft will crash making the first data point meaningless as you are choosing it at the starting point. Second, you are not just running one trial on one design but many trails on many designs. I suggest you try the math as the odds are reasonably high. This changes if you start talking about crashes since the first commercial flight, but those are again different numbers.
DuskStar 8y ago
Might also be worth considering P(2 Crashes | N Miles across 350 planes where at least one operator has incompetent maintenance), because that might not be all that different from P(1 crash | N Miles across 350 planes where all operators properly maintain their planes) Look at things like Alaska Airlines Flight 261 [0] - safe airframe, deficient maintenance, plane loses all pitch control and impacts ocean. Yes, this still means that Boeing needs to improve things - single points of failures are never OK on a plane - but it also doesn't (IMO) mean the plane is fundamentally unsafe without those fixes. 0: https://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261 https://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261
bjourne 8y ago
According to https://en.wikipedia.org/wiki/Aviation_safety#Evolution https://en.wikipedia.org/wiki/Aviation_safety#Evolution the fatal accidents per million flights were 0.39 in 2018. The MAX8 fleet has been operational for about six months. Assuming 3 flights per day: 350 * 6 * 30 * 3 = 0.189 million flights. To estimate the probability of two accidents, we can use a Poisson distribution with x = 2 and μ = 0.189 * 0.39 = 0.0737 P(x=2) = e^(-μ)μ^x / x! = 0.25% I.e your gut feeling is correct (if my math is correct, that is). If one uses the estimate from a sibling comment of 1 crash in 11 million fights, the probability decreases further to 0.01% Actually the correct calculation is: 1 - P(x=0) - P(x=1) = 0.26% since we are looking for the probability of there being more than one plane crash -- not just the probability of there being exactly two plane crashes.

Scoundreller 8y ago

I think I see a new product from LLoyd’d of London Syndicates: Early big double failure on new airframe insurance. A perfectly good airframe can have its reputation ruined with 2 incidents in a short time period.

objektif 8y ago

If they need time shouldn't the first course of action be grounding this aircraft?

KorematsuFred 8y ago

Better safe than sorry. For example if a plane crashes in the first flight should we just ignore it because it is statistically insignificant ? 2/350 seems like a fairly good number to ground the plane and do an investigation. In general this is good for aviation industry because next time Boeing will not cut corners as it has so far.