Singles v. Twins

[Nick Lappos]

Pprune Fan #1 said:

"This is why the comparative study of statistical percentages is so silly. It might have some relevance in a general sort of way to the whole industry, but it is meaningless to us individually. Just show me the cold, hard failure-rate numbers and let me draw my own conclusions without tossing in a fruit salad of other "criteria," thanka, thankavrymch (as Elvis used to say). "

Nick sez:
I guess I can't figure what exactly you mean, if anything. The numbers are just that, numbers, and they do represent the odds of an occurrence happening. You can believe them, disbelieve them or consider them silly, but your engine and transmission won't listen to you. Like a slot machine that has not paid out in the last 50 years, the odds on the next lever pull are exactly the same, because the little wheels in the machine can't remember the last outcome, since their memory is so poor.

You might consider it silly, but you don't seem to have a better idea. Perhaps you'd rather walk to the oil rig. Oh, gosh, the odds of drowning while walking to a rig are almost 1:1. What a silly number!

Stick your head in the sand, if you wish. Its your head!

Nick

PS I am revered only in some small circles, and only on alternate Tuesdays.

[Heliport]

TC
No. PPRUNE FAN #1 is most definitely not the Moderator in disguise.
Hang on. Because he was "jabbering senseless rubbish" you thought it was me!
Hmmm. Have to think about that one.

[almost canadian]

Maybe Lu is trying to make a comeback to the forum, or someone else is trying hard to fill his shoes.

Another quick view on stat's:
Let's say there is a lottery with 100 tickets to be sold, if one would buy all tickets 1 at the time, you could have the winning ticket after buying the first ticket or after buying the last one.
If your chances of having a failure are once every 200 years, this can also mean you have the failure in your first year, with the odds of another one happening in the next 199 close to nil.

The only factors that can increase the odds are an idiot at the controls and poor maintenance.

Here's another one for you #1: pedantic

pe·danti·cal·ly adv.
Synonyms: pedantic, academic, bookish, donnish, scholastic
These adjectives mean marked by a narrow, often tiresome focus on or display of learning and especially its trivial aspects: a pedantic writing style; an academic insistence on precision; a bookish vocabulary; donnish refinement of speech; scholastic and excessively subtle reasoning.

thanka, thankavrymch

[SASless]

Nick,

I hold your professional input in very high regard and hang upon ever word. Statistical analysis was a course in university that I managed not to sleep through and from that rare wakeful period of my education, I learned that it is not the numbers that count but the interpetation and more importantly the manipulation of those numbers. A for instance.......when you quote numbers, odds, rates, etc....for minor non-events like spindle slinging, blade launching, and nearly instantaneous airborne tranny dissassembly.....one must bear in mind....that you must factor the numbers to account for the fact very damn few people are ever going to survive the first event much less experience a repeated occurrence. I can assure you I do not ever wish to become a math lab experiment in probability determination for those kinds of things. Now coming from an erstwhile teetotaler like yourself, I can imagine your contemplation of these data would be improved by a few good Irish consultants....I would suggest employing oh say, Jamisons or something similar.

[Thomas coupling]

Heliport: no I didn't mean you talk rubbish, though I admit it looked like that when it came up in lights
However, this forum gets the odd nutcase 'popping in' now and again, and i do wonder why/who?
For instance:
What's happened to Flare Damit?
And now there's Pprune fan, or whatever he's called...definately a wind up

[SASless]

Wind UP's on Pprune.....oh, Sir...surely you say that in jest?

Who would stoop so low as to word a post merely with the base intent of doing some pprune fishing? It would take a person of very questionable parentage to do such a thing? I bet the best source of such shennigans lies with those who refrain from drink and other forms of male bonding like beer can shooting, stop sign sniping and other manly exploits. I bet Nick Lappos will never admit to participating in such endeavors being a renown teetotaller and Cobra pilot .

[widgeon]

eng_type ENG HUMAN MECH XSM (blank) Grand Total
REC 12 31 7 2 5 57
TS 8 37 4 8 57
TS2 1 7 1 9
Grand Total 21 75 11 2 14 123


Raining out today so I downloaded NTSB database for 2001 ,it is in an Acess format so you can run queries to you hearts content.
123 heli accidents reported last year , 21 where engine failure was initiating event , there are some in Human where cause was fuel starvation ( can t blame engine if we do not give it fuel!)
Rec = reciprocating , TS = turbine TS2 = twin turbine.
It is amazing the number of accidents casued during practice auto's WIll post that table later.

Darn table looks lined up on preview.

[Heliport]

TC
What's happened to Flare Dammit?
FD left a few months ago saying the forum was a waste of time or words to that effect and he'd never return.
I'm sure any similarity between Flare D's "I'm convinced that most helicopter pilots are neurotic nutjobs." and Prune Fan's comment on the EMS thread "I would say that you helicopter pilots are nothing but neurotic nutjobs, but I won't." is purely coincidental.

[Nick Lappos]

SASless,

Thanks for the Irish whiskey suggestions, but I generally partake of Bourbon when I am disproving your teetotaler assertions. I drove through Frankfort Kentucky a few years back, and saw the homes of many of my college friends, like J. W. Dant, Jim Beam, and the like. They were helpful in convincing me that staying in college and going to frat parties with Southern Belles was inferior to sitting on the ammo bay door of a Cobra, eating Beanie-Weenies! Some friends!

Nick

[B.Loser]

Well, since ya'll are including us neurotic nutjobs in the debate...,

...ya'll can throw numbers around 'til the cows come home, but the only cold hard numbers that anyone can count on are 50-50. You're either going to make it to your destination or your not. The engine(s), xmsn, d-line are going to work as advertised or they're not. (And you're either going to get out of the shower without slipping, falling and breaking your neck or you're not)

If you can't handle flying the singles, it's OK, there's no shame in that (I KNEW I couldn't write that with a staight face) - go get into your jamies and I or someother nutjob will take the mission - no big deal. That's what we're here for.

Reality bites. When the final call comes and it's time to go, it won't matter how many engines you have strapped on - it's . Adios.

[Cyclic Hotline]

#1 started this thread (where are you anyway #1?) with a quick commentary on helicopter safety then demonstrated the argument with a Pilatus PC-12 accident. As I don't know the details regarding this accident, I can't really make any comment on it.

I'll get to the helicopter stuff later, but in the interim, maybe read some revealing information on single engine airplane safety.

[helmet fire]

Doesn't two engines double the chance of having an engine failure??


But doen't surviving the failure depend upon the flight regime you are in? Twins might be twice as likely to have a failure, but they are significantly less likely to plumet to the ground with expletives when it does happen becuase their exposure to the OEI deadmans curve is generally (I stress the word GENERALLY) insignificant as a proportion of their total flight time, whereas the single engine aircraft is always operating in the OEI deadmans curve!!

Therefore, whilst you are more likely to have an engine failure in a twin - you are much more likely to survive engine failures because you are in a twin.

Clear as mud then?

[NigD2]

PPfan#1 a wind-up merchant........ definately.
This post keeping me entertained......... definately.
Nick L being tee-total......... maybe (SASLess should perhaps input some lat/long waypoints of favorite drinking establishments into Nicks GPS, although it may put him in the knocking shop next door knowing their accuracy).



A light hearted thread, I'm enjoying the wit and sarcy remarks from all.

[SASless]

GPS waypoints not needed for boozers kind fellow.....Chinook pilots are world renown for having an uncanny sense of priorities....any open door works if fumes of an alcoholic nature are wafting upon the breeze. Our favorite drinks are those of others......we would much rather spend your money than ours.....that is why I really like having Nicky Lamp-post along.....Uncle Igor's got a very thick wallet when it comes to marketing funds......please to remember Nick....I am looking for a helicopter....just cannot decide yet which model I like! Think you might be able to sway me into looking at a small fleet of 92's with the help of the old boy gang.....Old Overcoat...errr. Old Olderholt and his buddies?

[DeltaFree]

Lies, Damned Lies, and Statistics

What we want is useful statistics, allegedly all public transport even in a singles should ensure a crash/landing that will enable occupants to walk away though ac damage is acceptable. So what does this mean when night IFR is involved? I don't know so I will move on.
Most engine failures occur on multi engine ac ( sorry no stats just a guess), most of these go according to plan and a safe landing ensues, so engine failures are not a big problem! If on the other hand all ac were single engined how many failures would not result in injury? Give me those stats and I think an argument would be solved.
Regardless most shed blade, gearbox breakages and other similar incidents invariably do not result in smiley faces so how do we factor that one in?

[Nick Lappos]

DeltaFree,

Thanks for asking, "Give me those stats and I think an argument would be solved."

When safety is concerned, the issue is almost always the difference between perception and reality. I suggest some ernest wandering through the FAA data base (for accident stats, actual flight hours logged each year by type, and the like,) along with the NTSB site for accident narratives. Remember that the accident lists and pprune accounts almost always list the acidents, we are left to try and determine how many successful flights and near nisses there were between incidents through other means.

At the manufacturer, we get to see all the stuff, the latent failures seen in overhaul, the near misses, the crunchy sounding bits that are found on pre-flight, etc. This is a much more full account than the war stories (some misaccounted as they wander verbally through the community) we often get.

A few simple facts for us to debate:

1) The worst item in the aircraft, most failure prone, is the crew.
This is often because of poor planning and poor judgement. In helos the issue is lack of standardization for our operations, so we rely more heavily on judgement than airplanes. It can be argued that all airplanes land on the same runway, we just move it to different places for them! Helos make a living by being able to bend their operations to the environment, so they rely on the pilot to sort through all the factors and keep safe.

2) We tend to dwell on the worst of the worst, because we are human, and it makes juicier conversation. The fact that a statistic says we are exposed to a 1 in 1000 years probability doesn't phase us, we can still say it is unsafe. thats why sharks need the same press agent as dogs, cause dogs kill about 100 times more humans than sharks. Wanna pet a shark?

3) We practice what we can, and then imagine that is what happens. Engine failure is the most practiced emergency procedure, and one of the less likely. I asked my crew chief why he changed the K-28 relay to try and fix a snag once (when it was obviously the K-101 that was at fault), and he told me "I don't have a K-101 in stock, so I tried the other! We practice what we can, and this makes us think that what we practice will be what happens. Based on the real facts, we should practice crashing onto dark mountain sides and into wires!

4) We should devote the next dollar, and then next irate word, on the next most probable accident, knock it down as a cause, and go on to the next. Working systematically, aviation will get safer. Working hodge poge, we will kill all the sharks, and make not a whit of difference in safety.


I will post the best single source of accident data for those who wish to debate the facts, and not the proclivities they were taught through the Urban Legend School of Aviation Safety (I love it when I get nasty!!):


http://www.ogp.org.uk/pubs/300.pdf

The OGP server is down now, if it stays down, you can email me and I will send the document to you.

For pilot and airplane data in the US (raw numbers of hours, airplanes and pilots gives you the divisor for turning war stories into stats). As an example, there are over 200,000 airplanes in the US:

http://api.hq.faa.gov/clientfiles/CONTENT.htm

NTSB Accident data total:

http://www.ntsb.gov/NTSB/month.asp

NTSB query page, (search for helos and get 1235 accidents):

http://www.ntsb.gov/NTSB/query.asp#query_start


BTW, DeltaFree, "Give me" doesn't work where I come from, we usually depend on ourselves in this God-forsaken continent. The above sites I found in about 30 minutes of searching!

[widgeon]

Another note on the NTSB site you can download a complete year of information in Microsoft access format , which gives the narrative portion as well . Online database search is fine but you then have to go to the individual files to pull out the reasons. 2001 file was about 8MB zipped expands to about 34 MB unzipped. If any of you want the 2001 helicopters only info PM me and I will mail it to you ( is is only about 175KB excel file).

[DeltaFree]

Gobbledeegooked?

Thank you TC for your inspirational reply.
Perhaps my gobbledeegook was too gooky. The stats I would really want do not and cannot exist. As NL says reality vs perception is a big problem. Many conclusions can be drawn from stats, depending what argument you are trying to prove. The only true answer would come from stats covering exactly the same kind of work. In general singles are used when singles will do and twins are used when they are required so naturally their work cycles will be different.
Anyway most legislation comes from a perceived, and maybe not real, need for it. I am sure we can all think of rules that seem nonsensical, but someone perceived them as necessary.

[John Bicker]

Singles versus twins.

Yep, always will be, 'cause they are different obviously.

Totally agree with Mr Lappos. Most people have a very poor perception of "risk".

[Q max]

J Bicker

Yes - people are poor at stats.
... and you can 'bend' them all over the place.


Sure it's all about managing 'long odds' risks

These stats are from that Oil industry report which Nick quoted: (page 43ish)

#fatal accidents/----accidents/----#fatalities/---------#accidents/
100k hours----------100k hours----100k occupants-----100k flights

Single engine-------0.42------- 2.31-------0.18-------0.58
Light twin------------2.82-------4.22-------0.60-------1.38
Medium twin--------7.04--------1.85-------0.36-------0.62
Heavy twin----------0.52--------1.03-------0.07-------0.68
1998 totals----------0.77--------1.87-------0.30-------0.62

They seem to show singles being 'safer' !!!

(Could it be that the true data is intentionally supressed ?)

Apparently to experience a 1 in 10,000 chance of death you need to be airborn for 200yrs (surely you'd be dead before that)

or

5 mins on a Motorbike