Assuming independence. One could argue that the two engines do have some common failure modes such as fuel contamination, but for a SWAG just saying 2x is close enough.
Risk Tolerance
- Thread starter Mtns2Skies
- Start date
Assuming independence. One could argue that the two engines do have some common failure modes such as fuel contamination, but for a SWAG just saying 2x is close enough.
Zeldman
Touchdown! Greaser!
Next day I realized why an old man shouldn't be falling down and sliding in the mud ...
I hear ya, as much as it pains me to say it, part of the planning process before undertaking a risky activity includes a recovery period.
My biggest fear in life is being stuck in bed full of tubes and wires. And no idea of if or when I will get out.Light twins are apparently a handful with an engine out, too. But I hear you - I used to to fly quite a bit at night, but not so much anymore. Something like a Cessna 172 can be stopped in the space of a normal driveway and you can walk away - the airplane will be totaled, but if you keep the impact force horizontal versus vertical the sudden stop can be qiute short. Maybe getting in some practice on short field landings until they become old hat again? If your airplane is higher performance, maybe not, though. . .?
Zeldman
Touchdown! Greaser!
Yeah, well, see those twigs on the ground.?? Those can really hurt on landing and they stick in the wrong place...
Ted
The pilot formerly known as Twin Engine Ted
- Joined
- Oct 9, 2007
- Messages
- 30,014
- Display Name
Display name:
iFlyNothing
And apparently MU-2s are impossible to handle on one, and will automatically and immediately crash if you ever lose an engine.
(me flying an MU-2 on one engine... during initial training, no less so with almost 0 hours in type. Complete non-event)
Call me goofy, but I always liked the look of the MU-2. And I saw a warbird Cessna mixmaster for sale recently - I could probably flyt that. . .And apparently MU-2s are impossible to handle on one, and will automatically and immediately crash if you ever lose an engine.
(me flying an MU-2 on one engine... during initial training, no less so with almost 0 hours in type. Complete non-event)
Ted
The pilot formerly known as Twin Engine Ted
- Joined
- Oct 9, 2007
- Messages
- 30,014
- Display Name
Display name:
iFlyNothing
I always loved the look of the MU-2, part of what attracted me to it.
Interestingly, its utilitarian look seemed to respond well with Cloud Nine fans/donors. Maybe the perception of something that looks more like it's purposeful and there to do a job, vs. say the 310 and 414 which looked far more elegant and not like a freight dog... er... dog freighter.
EdFred
Taxi to Parking
Take a fair coin. This represent the engine. Heads keeps the engine running, tails in this case fails.
Flip it an infinite number of times and you're going to get a 50% chance the engine fails.
However when you add the second coin to the mix you don't end up with a 100% chance of failure. You end up with:
25% chance neither engine fails. (H H)
50% chance one engine fails. (H T or T H)
25% chance both engines fail. (T T)
But it's NOT a 100% chance an engine fails. Bad math.
C = (1-p)^n
p = failure rate
n = number of engines
- Joined
- Jun 7, 2008
- Messages
- 24,123
- Display Name
Display name:
Bob Noel
Let p1 be the probability of a random engine failure per hour (or whatever unit you wish).
If you have two engines, the probability of a failure of at least one engine is p1 + p1.
or am I remembering my reliability probability calculations wrong?
If you have two engines, the probability of a failure of at least one engine is p1 + p1.
or am I remembering my reliability probability calculations wrong?
EdFred
Taxi to Parking
My chances of winning on a lottery scratch-off are 1 in 4. But buying 4 tickets doesn't guarantee a win. Same thing here.
s35pilot
Pre-Flight
You need to have one left to get you to the seen of the accident!
Sinistar
En-Route
- Joined
- Sep 9, 2016
- Messages
- 3,735
- Display Name
Display name:
Brad
Add BRS to the Skywagon. Then you can fly with the confidence swagger of a Cirrus Pilot.
Not sure of your age - transitioning from a single to twin early in your flying and younger would seem wise/doable. I'm getting closer to 60 and pretty sure I'd be more likely to screw up in a Twin than a Single. Or as someone else suggested earlier. Transition to something slower.
I think the OP is Wisconsin? Every time I've flown from the Twin Cities up into to the UP and Houghton theres a lot of cruise time over a billion trees that gets the mind to wandering about funny noises. That wicked cold lake just to North doesn't help - especially when its LIFR but right at the shoreline its CAVU.
Not sure of your age - transitioning from a single to twin early in your flying and younger would seem wise/doable. I'm getting closer to 60 and pretty sure I'd be more likely to screw up in a Twin than a Single. Or as someone else suggested earlier. Transition to something slower.
I think the OP is Wisconsin? Every time I've flown from the Twin Cities up into to the UP and Houghton theres a lot of cruise time over a billion trees that gets the mind to wandering about funny noises. That wicked cold lake just to North doesn't help - especially when its LIFR but right at the shoreline its CAVU.
- Joined
- Mar 10, 2013
- Messages
- 19,681
- Location
- Oakland, CA
- Display Name
Display name:
Bro do you even lift
this is why we need THREE ENGINES
Daleandee
Final Approach
- Joined
- Mar 4, 2020
- Messages
- 6,995
- Display Name
Display name:
Dale Andee
Mongoose Aviator
Line Up and Wait
While flying my twin, if one of the engines goes out, I am not looking for the closest place to land. I am looking for the best place to land. I would prefer a 6000' runway with emergency equipment available in case I botch the single engine landing. I am capable of flying extended distances on one engine. I have also done actual engine shutdown and restart in-flight while training such that depending on the reason for the engine failure, there is plenty of time to try an in-flight engine restart. A significant restriction on my twin when flying or landing on one engine is a seriously reduced rate of climb so as to make a go-around most unlikely to be successful. Hence, if I am coming if for a landing on one engine, I will get one attempt.
With two engines, I am comfortable landing on a narrow 2500' runway. For a single engine landing in the twin, I would prefer a wider 6000' runway. I fly in the NE portion of the US such that a good selection of airports is very feasible.
- Joined
- Jul 17, 2019
- Messages
- 1,988
- Location
- Chicago suburbs
- Display Name
Display name:
The Little Arrow That Could
It's an easy thing to get tripped up on, especially when using 50% odds and thinking in terms of twin engines (conveniently lets you get to 100%). I think a straightforward illustration to show that this logic couldn't be correct is picking a p1 > 50%.
Let p1 be 90% chance of failure.
2 engines: p1+p1 = 180%. Of course that can't be correct, it can't be >100%.
It'd be the chance of any engine failure, which in this case would be:
0.9*0.9 (both fail) + 0.9*0.1 (engine 1 fails, engine 2 works) + 0.1*0.9 (engine 1 works, engine 2 fails) = 0.81+0.09+0.09=99%.
steingar
Taxi to Parking
Give me an example of another airplane the suffered CFIT with sudden and complete stoppage where the folks inside walked away. I'll wait.
EdFred
Taxi to Parking
I fly a Cirrus sometimes - nice airplane (SR20, 2007) but the 'chute is, I think, more marketing hype than a big safety umbrella. Like all chutes it has altitude and speed constraints - they claim a lot of "saves" but for the ones that aren't loss of control in IMC or mid-airs that don't kill outright, I'm inclined to think the saves are exaggerated - there was likely a good probability of a successful forced landing in many of those. It's not a religion thing with me - I don't mind the chute being there, but it COULD be I'd opt for a forced landing on a flat surface versus an uncontrolled impact equivalent to a seated ten foot drop.
- Joined
- Mar 10, 2013
- Messages
- 19,681
- Location
- Oakland, CA
- Display Name
Display name:
Bro do you even lift
Shepherd
Final Approach
My PA-17 is so light, and slows down to about 35-40 miles an hour (still trying to figure out the actual stall speed) so even putting it in a tree is survivable.
Since there is no way to restart the engine if it quits in flight, a possible engine out is always somewhere in the back of my mind. As a result everything I fly over gets scrutinized for landing and probable consequences. Every spot gets categorized: Fly it out, trailer it home, staying where it is, and have a hearse on speed dial.
Since I don't have an electrical system the whole solo night flying is moot. I do fly at night, but only in the 172 or Cherokee, and only with a friend.
Mitigating risks and thinking through the consequences is what we all do, every time we walk up to a plane.
Since there is no way to restart the engine if it quits in flight, a possible engine out is always somewhere in the back of my mind. As a result everything I fly over gets scrutinized for landing and probable consequences. Every spot gets categorized: Fly it out, trailer it home, staying where it is, and have a hearse on speed dial.
Since I don't have an electrical system the whole solo night flying is moot. I do fly at night, but only in the 172 or Cherokee, and only with a friend.
Mitigating risks and thinking through the consequences is what we all do, every time we walk up to a plane.
- Joined
- Mar 15, 2016
- Messages
- 4,946
- Display Name
Display name:
Ari
Yeah, but you'd look good in a Duke!
For me, the risk calculus isn't about numbers. Some factors can't be quantified (what is the chance of the engine picking night IMC in the mountains to quit instead of a CAVU day over a straight stretch of highway?), some are subjective (what is the chance of the critical engine in my twin failing the day before my recurrent training instead of the day after?), and there is no objective formula for the go/no-go decision.
By my math, if your ticket was punched "N414RS crash" you had a 20% chance of it being as the pilot and 80% chance of it being as the occupant of a house. Your odds get better on the ground if your ticket read "N7022G crash," 50% chance as pilot and 50% chance as UPS driver in your truck. I'm going to make the smartest safety decisions I can each time I fly, but I'm not going to stay out of airplanes just because they can crash. But I also won't fault anyone whose math is different from mine, or if your math changes from 2 weeks or 2 decades ago.
TL;DR: These discussions are really about petting Schroedinger's cat.
- Joined
- Sep 19, 2005
- Messages
- 9,486
- Display Name
Display name:
Pilawt
No Photoshop:
Piper PA-32-3M, first flight 5/13/1965. Proof-of-concept prototype for what eventually morphed into the PA-34 Seneca.
- Joined
- Mar 10, 2013
- Messages
- 19,681
- Location
- Oakland, CA
- Display Name
Display name:
Bro do you even lift
mine was absolutely 100% not photoshopped!
- Joined
- Oct 16, 2019
- Messages
- 6,353
- Location
- Atlanta / Marietta
- Display Name
Display name:
Vintage Snazzy (so my adult children say)
A few thoughts:
1) Why the love for Aerostar? A safe choice perhaps, but are you willing to actually ride in one?
2) Being a little more serious, moving your risk tolerance as you get older isn't a bad thing. Flying at night is hard, and as we get older eyesight isn't what it used to be, etc. And it's not that we're being unreasonably cautious, but perhaps more that we use to assess risk too lightly in our younger years. Nothing can happen to me!
If for you flying at night with your current experience and abilities is at the limit, then lot of great ideas already posted on flying higher, weaving to fly over airports, etc.
3) I'm still waiting for someone to suggest night vision goggles.
1) Why the love for Aerostar? A safe choice perhaps, but are you willing to actually ride in one?
2) Being a little more serious, moving your risk tolerance as you get older isn't a bad thing. Flying at night is hard, and as we get older eyesight isn't what it used to be, etc. And it's not that we're being unreasonably cautious, but perhaps more that we use to assess risk too lightly in our younger years. Nothing can happen to me!
If for you flying at night with your current experience and abilities is at the limit, then lot of great ideas already posted on flying higher, weaving to fly over airports, etc.
3) I'm still waiting for someone to suggest night vision goggles.
This started when I made the statement that an engine failure is twice as likely in a twin as in a single engine plane. You called that "bad math," so let's actually do some basic statistics.
- Let P be the probability of an engine failure. Then the probability of an engine not failing is (1 - P).
- For a twin, the probability of completing a flight with both engines operational is then (1 - P)(1 - P), or (1 - P)^2.
- It follows then that the probability of NOT completing a flight with both engines running is 1 - (1 - P)^2. That becomes 1 - (1 - 2P + P^2), which simplifies to 2P - P^2.
- Given that P is a very small number, P^2 is an extremely small number, and given the quality of our data about P in the first place, it is reasonable to say 2P - P^2 ~ 2P.
- For a twin, the probability of completing a flight with both engines operational is then (1 - P)(1 - P), or (1 - P)^2.
- It follows then that the probability of NOT completing a flight with both engines running is 1 - (1 - P)^2. That becomes 1 - (1 - 2P + P^2), which simplifies to 2P - P^2.
- Given that P is a very small number, P^2 is an extremely small number, and given the quality of our data about P in the first place, it is reasonable to say 2P - P^2 ~ 2P.
IOW, the probability of an engine failure for a twin is twice the probability of an engine failure for a single engine plane (2P) plus the tiny probability of having both engines fail (P^2).
Neglecting that tiny additional P^2 term, the probability of an engine failure in a twin is indeed approximately twice the probability of an engine failure in a single.
QED
Last edited:
EdFred
Taxi to Parking
You’ll have to explain that fuzzy conclusion.
And if you don’t like the approximation, use the exact form, 2P - P^2.
With sample numbers, let’s assume the probability of an engine failure is 1x10^-4, or 0.0001. 2P = 0.0002 whereas the exact form is 2P - P^2 = 0.000199990.
You object to that slight inaccuracy, when we don’t know P within 3 significant figures in the first place?
Last edited:
flyingcheesehead
Taxi to Parking
Seems perfectly normal. I wasn't afraid of heights when I was a kid, and I thought it was kinda weird that my dad was. When we re-sided the house together when I was about 13, he was on the ground with the saw and I was on the scaffolding. Now, while I'm still OK being on a ladder 10 feet off the ground, I dislike anything that would result in a trip to the hospital or worse, and if I so much as look at a picture of certain things it turns my stomach. The more we live, the more we realize how much there is to live for.
Well... Now that I'm working in aviation safety, I have learned that it is not at all the "stay on the ground if you want to be safe" approach that many PoAers think it is.
Basically, it's all about the loop: 1) Identify the risk (and its root causes), 2) Mitigate the risk, 3) Accept the remaining risk, 4) Fly. If the remaining risk in #3 is unacceptable, you go back to step 1 until it is either acceptable or you decide the mission isn't worth doing.
So, in your case, let's look at flying at night in your C180, with the main risk you're looking at here being the possibility of an engine failure leading to an early transition to the unalive.
I'm going to start the root cause analysis from that last bit. Why did you die? Plenty of possibilities, but I'll stick with two main ones:
- Hypothermia or other forms of exposure
- Blunt force trauma
- Hypothermia or other forms of exposure
- Insufficient survival gear
- Slow search and rescue response
- ELT or PLB not present or working
- Not on a flight plan
- Not speaking with ATC
- Crashing far from help or in a difficult-to-reach place
- Flew direct over unpopulated or inhospitable area
- Blunt force trauma or other injury
- Too much energy transferred to your body too quickly during the crash sequence
- Lost control of the airplane in the air (vertical energy transfer)
- Came to a sudden stop (horizontal energy transfer)
- Couldn't see well enough to find a large enough clear area to slow down
- Clear area not within glide range
- Too much energy transferred to your body too quickly during the crash sequence
- Engine failure (this is essentially a subitem of every single thing above)
- Fuel Exhaustion
- Induction blockage
- Carb ice
- Mechanical Failure
- Insufficient backup systems (aux fuel pumps, mags, etc)
- Insufficient maintenance
- Don't fly in the winter or over inhospitable terrain (* SEE BELOW. I'm not actually saying "Don't do this".)
- Carry relevant survival gear
- **
- Keep up with ELT battery requirements, and carry a PLB with a good battery
- File a flight plan - IFR if you're equipped and rated, VFR otherwise *
- Talk with ATC. This is pretty much a given on that IFR plan, but get flight following if you're VFR.
- Plan your route to stay relatively near airports, highways, or reasonably populated areas
- (Same)
- **
- **
- On a regular basis, get flight instruction in handling this sort of emergency, and practice it even more frequently. Same with stalls and other loss-of-control stuff.
- **
- Get yourself some bad-ass bright landing lights so you have more time to see where you're landing and avoid obstacles
- Cruise at a higher altitude so that you have more options and time.
- **
- **
- Carry lots of extra fuel.
- **
- Ensure carb heat is working, AND either Study conditions along route of flight for susceptibility, AND/OR get an engine monitor with a carb temp probe and preferably an alarm in the danger zone.
- **
- Install backups as available
- Perform not only required regular maintenance but also proactive maintenance.
** Some of these things are too general to be directly mitigated, or otherwise difficult to mitigate. So, perform mitigations elsewhere on that path in the chain.
Now, evaluate the risk that remains. Do you feel comfortable with the flight now? If not, take the things that you're still uncomfortable with and re-evaluate them. If you can't get to the point that you feel comfortable enough with the flight to make it worthwhile, then don't go.
To some extent, we all do this process intuitively on every flight. I don't sit here and do a risk analysis prior to hopping in my Mooney and blasting into the sky on a sunny VFR day. That's a level of risk that I am very comfortable with accepting.
It's the flights that make you uncomfortable where you've decided that things are too close to your risk tolerance for the day where it's worthwhile to go through this process. You'll either get to the point where you are comfortable with the flight, or you won't... And at that point, the decision is much easier.
It's a reasonable approximation frequently made in engineering analysis. I'd say @Half Fast 's reasoning beats a coin flipping analogy.
- Joined
- Jul 23, 2021
- Messages
- 3,916
- Display Name
Display name:
Albany Tom
I'm going to make a different argument. If you're flying for fun, it should be for fun. If it's not fun, then don't do it. Maybe you just need a break, or should take some time to do something else. I believe that sometimes in hunches or bad feelings, we're got some data in our head that we've processed as a set of things that are "weird" and put fear around that, that could be justified and real. But we don't know what it is, because we don't have enough information about it to come to a clear conclusion. Just my 2 cents.
- Joined
- Apr 23, 2013
- Messages
- 6,689
- Display Name
Display name:
3G
Aviation Consumer ran the numbers a few years ago. Engine related causes of accident was something like .25 per 100,000 flight hrs.
Lycoming likelihood was about .9 per 1,000 motors. Continental was close to double that likelihood at 1.15 per 1,000 motors.
The interesting quote is “For both Continental and Lycoming, single-engine failures are more survivable than twin-engine failures by a wide margin. For both Lycoming and Continental, engine failures in twins are twice as likely to be fatal as a failure in a single-engine airplane. “
For the rest of the story: https://www.aviationconsumer.com/safety/why-engines-quit-failures-are-avoidable/
Lycoming likelihood was about .9 per 1,000 motors. Continental was close to double that likelihood at 1.15 per 1,000 motors.
The interesting quote is “For both Continental and Lycoming, single-engine failures are more survivable than twin-engine failures by a wide margin. For both Lycoming and Continental, engine failures in twins are twice as likely to be fatal as a failure in a single-engine airplane. “
For the rest of the story: https://www.aviationconsumer.com/safety/why-engines-quit-failures-are-avoidable/
- Joined
- Mar 15, 2016
- Messages
- 4,946
- Display Name
Display name:
Ari
If P = 1x10^-4, then P^2 = 1x10^-8 and 2P + P^2 = 0.00020001. And (2P + P^2) / (2P) = 1.00005. Even with P = 1x10^-2 (a pretty crummy engine!), (2P + P^2) / (2P) = 1.005. I’m pretty comfortable saying that a half a percent maximum error in the formula is “approximately” correct, especially for input numbers that are best obtained from the chaos theorists.
Mongoose Aviator
Line Up and Wait
For additional context, here is another quote from the mentioned article:
"We don’t have any data on how many multi-engine pilots take care of business and return to the airport after an engine tanks because these may be rarely reported."
If somebody is uncomfortable in a twin than by all means stay in the single. Don't fly outside your comfort zone.
I fly both single and twin and choose which one based on what is involved with the flight.
In terms of all the fancy probability stuff in a myriad of other postings, my interest lies in the realistic probability of me being in an aircraft with no operational engine whether that is the single or the twin.
jesse
Touchdown! Greaser!
I can't remember how many hours I have in twins, but its laughable. Even with minimal experience, I'd rather deal with an engine failure at night in a twin vs a single any day of the week. If I don't like the way the world looks on one engine in a twin, I can simply shut the ****ing engine off. If I don't like the way the single looks as a glider, I can't start half the engine back up.
Anyhow, I think the risk thing is normal. The winter IMC **** I did in my 20s in airplanes that usually didn't even have functional pitot heat would be of zero interest to me today. I've also found that each decade of age adds about ten to fifteen more miles of buffer to thunderstorms.
If you ever want to practice engine failures, I moved to WI earlier this summer and now live about ten minutes from 8D1.
Anyhow, I think the risk thing is normal. The winter IMC **** I did in my 20s in airplanes that usually didn't even have functional pitot heat would be of zero interest to me today. I've also found that each decade of age adds about ten to fifteen more miles of buffer to thunderstorms.
If you ever want to practice engine failures, I moved to WI earlier this summer and now live about ten minutes from 8D1.
Last edited:
I'm mainly uncomfortable with the cost of flying a twin.
- Joined
- Jul 17, 2019
- Messages
- 1,988
- Location
- Chicago suburbs
- Display Name
Display name:
The Little Arrow That Could
EdFred
Taxi to Parking
If P is .5 how can you end up with a greater than 100% chance? [(2*.5) + .25] You can't. Well, evidently YOU can.
Going past 50%, you're saying there's a more than 200% chance that something will occur if the probabilities are 75% for each one.
.75 + .75 + .5625
Recheck your math.
Last edited:
Ted
The pilot formerly known as Twin Engine Ted
- Joined
- Oct 9, 2007
- Messages
- 30,014
- Display Name
Display name:
iFlyNothing
The key omission from that quote is the survivability of engine failures that are reported in piston aircraft.
The vast, vast majority of engine failures in piston twins never make an NTSB report, because there is never an accident or an incident. Engine fails, fly to another airport, land. The ones that make it to the NTSB are the ones where the pilot ****s up and then balls it up.
Yes, those are sad. I've read some that are just gut wrenching, and in virtually every single one I want to find the pilot who crashed and smack him silly for making such blatantly obviously poor decisions. It really isn't that hard to not make terrible decisions with these things. Twins that were certified under Part 23 (or CAR 3) had allowances for how controllable they had to be. Sometimes, yes, it's just a failure at a bad time and there's not much you can do about it (421 engine failures on takeoff are an example, which were surprisingly common for a few years). But let's consider something like @Jim K 's oil issue that resulted in a precautionary landing. I had almost the same thing happen in a first year tuna tank 310 on a ferry flight, I suppose it was about 9 or 10 years ago (by the way, fantastic flying airplane). What'd I do? Shut the engine down, declared an emergency, had a single engine landing. Found the source of the problem, added oil, completed the ferry flight. Complete non-event and the engine ended up being fine.
I also read on the internet that MU-2s are terrible in icing. I was reminded by the interwebz that 3 years ago, this is what I landed the MU-2 in:
That was a fun risk management one. I had landed in Missoula MT the night before, having shot the ILS 12 Z down to a few hundred feet above minimums (look that one up). Departed pre-dawn runway 12 with clouds around OVC 004 as I recall, look up the departure procedure on that one. Never been in there before.
While on the flight home from MSO to IXD, a bit over halfway (which is staunchly through the middle of nowhere) I had a fuel boost pump failure, a caution light for which the manual has a very poor description of what it means or what to do. However, I took "Land as soon as practical" (vs. "Land as soon as possible") to mean that it wasn't likely to cause any damage or engine failure.
Although the weather en route was clear, all of the airports looked snow-covered, no towers anywhere, certainly no maintenance or anyone familiar with the MU-2. But, I also knew the snow/icing on approach back home. I decided to continue to monitor the behavior of that engine, shut it down and land if there was an issue, but keep pressing towards home where I had maintenance facilities and knew the runways would be plowed.
I don't really miss flying, but I do miss flights like that. Those were fun.
midwestpa24
Final Approach
The majority of multi engine airplane crashes that started with a single engine failure result because the pilot was unwilling to accept the performance available, and tried to maintain altitude or climb when it just wasn't there, the famous VMC roll overs. A large part of my multi training, and the check-ride, was understanding that the second engine may not keep you in the air, and in some cases may just extend your glide. You have to treat an engine failure in a twin just like an engine failure in a single. Airspeed is life in a twin, and if you have to put the nose down to get airspeed, so be it. Far far better to arrive at the ground wings level under control, than vertically after a VMC roll.