Why Twins Aren't Safer than Singles

VWGhiaBob

VWGhiaBob

Line Up and Wait
Joined
Mar 17, 2013
Messages
884
Display Name
Display name:
VWGhiaBob
:dunno:

So...I'm just getting back into flying after a 25 year break and was thinking twins this time instead of singles.

That is, until I read every article I could find on the topic. Basically, if you read all the research, twins are safer under very limited circumstances and more dangerous in many.

A reason why occurred to me last night, other than the obvious ones I've read (e.g., hard to control on one engine). It's this: In a twin, you are at least TWICE AS LIKELY to have an engine fail, because you have, well, two engines. That means you are 2 times as likely to be in a situation that requires skilled piloting under extreme stress. Add to that the faster landing speed, and the all too likely loss of control, and you start to understand why the safety record isn't necessarily better.

Granted, twins under ideal conditions can make it to a runway on one engine. But I have also learned that in the real world, many twins can't maintain altitude on one engine with any kind of load (despite specs to the contrary), so you may not be going down to a runway anyway.

It has been a real head scratcher for me on why twins aren't that much safer. Now I think I'm getting it. I may just stick with singles, but would be interested in other thoughts. :blueplane:
 
Higher speeds and weight make for a drastically higher kinetic energy on a approach landing..
 
light twins generally won't maintain altitude on one engine, even lightly loaded they may not maintain the altitude you need. (and certainly may not have the climb performance)

It takes the disipline to not take off at gross, and to maintain proficiency.... All while burning twice the gas..
 
Meh. I don't agree that twins are more unsafe. It all depends on what you are comparing to. Are we talking training aircraft like a Seminole versus an Archer? A Piper Meridian is not safer than a Cheyenne. Loading a 172 on a hot day to gross results in the same crappy performance just as a Seminole would. Your chances of becoming a glider in a single engine airplane when the engine fails is 100%. Chances of becoming a glider in a twin are much less. And while light twins may not maintain altitude, a single will definitely NOT maintain altitude and that is a guarantee. And arguing over the kinetic energy of light twins is laughable. Light twins might buy you a little time to the impact site at best, but its better than having less than a litte time. Managing 2 engine might make them more complex, but by that vertue does not make them more unsafe. Pilots have a greater chance of screwing up if they panic and that might increase the percentage for something to go wrong.
 
Inverted said:
Meh. I don't agree that twins are more unsafe. It all depends on what you are comparing to. Are we talking training aircraft like a Seminole versus an Archer? A Piper Meridian is not safer than a Cheyenne. Loading a 172 on a hot day to gross results in the same crappy performance just as a Seminole would. Your chances of becoming a glider in a single engine airplane when the engine fails is 100%. Chances of becoming a glider in a twin are much less. And while light twins may not maintain altitude, a single will definitely NOT maintain altitude and that is a guarantee. And arguing over the kinetic energy of light twins is laughable. Light twins might buy you a little time to the impact site at best, but its better than having less than a litte time. Managing 2 engine might make them more complex, but by that vertue does not make them more unsafe. Pilots have a greater chance of screwing up if they panic and that might increase the percentage for something to go wrong.
Click to expand...

:yeahthat:

...and I think it depends on where you do most of your flying. If you do a lot of flying in western colorado then obviously a single will be safer than a typical light twin such as a Seminole. But if you fly between islands around florida than any twin will be much safer as long as it can hold 5ft AGL OEI.
Now if you do a lot of flying in the mountains then spend a bit more money and buy a twin that can hold altitude.

I personally wouldn't worry about accidently spinning it, if you spend enough time training and stay proficient you should be fine even when you loose an engine on take off at MGTOW.
 
Fly what you like. Bu don't take the gross stereotypes as gospel.

Lots of things that would end up as NTSB reports in singles go unreported in twins. A safe OEI landing is no big deal in a twin.

Further, there are answers to the Vmc rollover issue, not counting centerline thrust twins. Counter-rotating props, VGs, extended wingtips all serve to improve OEI handling. Some twins even have stall speeds above Vmc, so just don't stall the wing, mmmkay? How do singles fare when they stall on final?

Twins also tend to have other redundancies. Two vacuum pumps are nice in IMC when one takes a dump. Two hydraulic pumps mean you can get the gear down while you'd be belly scraping a single. Etc...

Lastly, there is the whole point of having more time between an engine failure and terra firma. Just like a turbo getting you to FL200 gives you more glide distance so does a spare fan. You're still not going to go around or shoot the missed approach. But with some proficiency you should make paved runway rather than off-field.

Where is your mission? Do you regularly cross rough or watery terrain at night? I do. I want a twin.
 
Morne said:
Fly what you like. Bu don't take the gross stereotypes as gospel. Lots of things that would end up as NTSB reports in singles go unreported in twins. A safe OEI landing is no big deal in a twin.
Click to expand...
:yes:

The single vs twin debate has raged for years. You cannot make blanket statements about twins anymore than you can about singles; a Beechcraft G36 is hardly the same as a Cessna 152 and a Beechcraft G58 is hardly the same as a Piper Seminole. Each aircraft has its features and its costs. Each owner needs to decide on his/her mission, priorities and budget.

The quote on "twice the gas"; again, gross generalization that is both true and false. Does my BE58 burn twice the gas of a 172; true, but hardly a real comparison. For years I flew a Piper Turbo Lance that burned 20 GPH now I fly a Baron that burns 25 GPH; equivalent seating and interior space but the Baron is 20 knots faster, provides 500lbs more payload, 600HP vs 300HP on takeoff, FIKI, Radar, redundant electrical and pressure systems and looks much cooler :wink2:.

I personally fly a twin because for me it and my mission I am safer. I fly for business and pleasure year round, day and night, in hard IFR weather with passengers. I flew several different singles for many years and was simply uncomfortable with night, IFR, and winter operations with a non-FIKI single engine (single system) aircraft.
 
Too many variables, and it's been pretty well stated above. The biggest issue is poorly handling an OEI situation. The other one is choosing to fly into worse weather, but Cirrus is changing that balance with their pilots who think the plastic wonder is good for anything.

I've had a number of mechanical failures in a twin that were non-events. Vacuum pumps, fuel pumps, magnetos, alternators, etc. In all cases I've had enough redundancy that it wasn't something to worry about. That by itself is huge since I think nerves more than anything are what kill pilots in emergency situations. I've never had a real engine failure, but I have landed with one feathered intentionally twice. No problem.

OEI performance is highly variable depending on weight and the aircraft. Right now I fly a Colemill 310 with 300 HP a side. OEI performance is comfortable. Not turbine-like, but I don't worry about hitting terrain east of the Rockies, even if heavy. Of course flying lighter is better when practical.

Buy what you want, train, fly.

As for why I fly twins, our mission dictates it. Lots of flying in very remote areas with no landing options, or where system failures without backups will cause big problems. A single is just too much risk for that, more than I'm willing to accept.
 
Last edited:
VWGhiaBob said:
...Basically, if you read all the research, twins are safer under very limited circumstances and more dangerous in many....
Click to expand...
you have that backwards

Typically it takes 8-10 seconds from the time I pass the point rolling on the runway that I can't stop at the end, till I have the wheels up climbing at 120mph (20mph over blue line). That 8-10 seconds will be followed by 4 hours flying over the ozarks and appalacians in the dark, during which time an engine failure will be a non-event.
 
Shut up all of you!!!
Shut up! Shut up! Shut up!




You're all going to have me looking at Twinkies.
 
I've been telling Ed to look at a Twinkie since he boight the kie in the first place. ;)

JetStar...
 
VWGhiaBob said:
:dunno:

So...I'm just getting back into flying after a 25 year break and was thinking twins this time instead of singles.

That is, until I read every article I could find on the topic. Basically, if you read all the research, twins are safer under very limited circumstances and more dangerous in many.

A reason why occurred to me last night, other than the obvious ones I've read (e.g., hard to control on one engine). It's this: In a twin, you are at least TWICE AS LIKELY to have an engine fail, because you have, well, two engines. That means you are 2 times as likely to be in a situation that requires skilled piloting under extreme stress. Add to that the faster landing speed, and the all too likely loss of control, and you start to understand why the safety record isn't necessarily better.

Granted, twins under ideal conditions can make it to a runway on one engine. But I have also learned that in the real world, many twins can't maintain altitude on one engine with any kind of load (despite specs to the contrary), so you may not be going down to a runway anyway.

It has been a real head scratcher for me on why twins aren't that much safer. Now I think I'm getting it. I may just stick with singles, but would be interested in other thoughts. :blueplane:
Click to expand...

I made the runway 3 times after small issues such as oil lines caused me to secure an engine in flight, once was on a below minimums ILS. No problems and my repairs were low cost and had me flying out shortly thereafter. That was in my low power Beech Travelair. I figure the ability of the extra engine to allow me to shut down the other saved me on the order of $50,000 in engine repairs.

You can skew statistics to make them read whatever you want, but the reality is, twins typically make it to a runway after they lose an engine, also quite comforting on those dark nights over bad terrain. The ability to do three miles a minute in econo cruise isn't too shabby either.

There are some performance corners where some twins won't fly on one, but it's nothing like what you're making out.
 
Last edited:
I have flown both single and twin for many years.
The past 15 years has been almost exclusively twin.
Reason?
Well, it is the Great Lakes and to go any direction other than due South means over water. Flying is often done when the water is too cold for survival and the return leg of the flight is in the dark.
Ignoring the much discussed take off failure, a twin simply gives me more options.
Now an Apache is not much of a twin. It is not much of an airplane compared to the Baron's etc.
I gave up a Super Viking (loved it for 10 years) for the Apache. That happened when my flying became less about going to Sun-N-Fun and more about hauling a load of grandchildren around.
This particular Apache has been flying over the lakes for over 50 years. Seems to work.
 
Baron2PG said:
:yes:

The single vs twin debate has raged for years. You cannot make blanket statements about twins anymore than you can about singles; a Beechcraft G36 is hardly the same as a Cessna 152 and a Beechcraft G58 is hardly the same as a Piper Seminole. Each aircraft has its features and its costs. Each owner needs to decide on his/her mission, priorities and budget.

The quote on "twice the gas"; again, gross generalization that is both true and false. Does my BE58 burn twice the gas of a 172; true, but hardly a real comparison. For years I flew a Piper Turbo Lance that burned 20 GPH now I fly a Baron that burns 25 GPH; equivalent seating and interior space but the Baron is 20 knots faster, provides 500lbs more payload, 600HP vs 300HP on takeoff, FIKI, Radar, redundant electrical and pressure systems and looks much cooler :wink2:.

I personally fly a twin because for me it and my mission I am safer. I fly for business and pleasure year round, day and night, in hard IFR weather with passengers. I flew several different singles for many years and was simply uncomfortable with night, IFR, and winter operations with a non-FIKI single engine (single system) aircraft.
Click to expand...

Yep, I don't use twice the gas of a C-210, I use 21gph total to do 180kts, a 210 uses 17 to do 160 so I get 8.5 mpg and it gets 9.5mpg, that's 11% more not 100%. Now we get to the other part of that and that is I'm running just under 60% power way LOP to get that speed, my engines are loafing just barely solid on the pipe fat dumb and happy, they'll run like that with no complaint forever. The 210 is always throttled up ROP to do 160, talk to HP single owners about cylinder replacement.

What the second engine buys you is options.
 
VWGhiaBob said:
A reason why occurred to me last night, other than the obvious ones I've read (e.g., hard to control on one engine). It's this: In a twin, you are at least TWICE AS LIKELY to have an engine fail, because you have, well, two engines. That means you are 2 times as likely to be in a situation that requires skilled piloting under extreme stress.
Click to expand...

This statement is incorrect, you are not twice as likely to have a failure. This is a pretty basic probability problem.

Say each engine has a 5% chance of failure. The chance of one failure out of two engines would be .05*.95= .0475 So the chance of one out of two engines failing is 4.75% in a twin versus 5% in a single. You're chances of a single engine failure actually go down in a twin.

Redundant systems don't increase the chance something will go wrong, however removing systems does decrease the chance they will fail ;)
 
EdFred said:
I know. Except the insurance actually is twice as much.
Click to expand...

Well, that isn't true either...sorry. Once you have a few hundred hours under your belt the insurance cost basically is a function of the hull cost plus liability. No different than a single...
 
Baron2PG said:
Well, that isn't true either...sorry. Once you have a few hundred hours under your belt the insurance cost basically is a function of the hull cost plus liability. No different than a single...
Click to expand...

Even that isn't necessarily accurate. When I bought my Travelair having 60hrs TT and a PP my insurance was $1100, $800 cheaper than my insurance man could get me insured in a Bonanza.
 
guardrail said:
This statement is incorrect, you are not twice as likely to have a failure. This is a pretty basic probability problem.

Say each engine has a 5% chance of failure. The chance of one failure out of two engines would be .05*.95= .0475 So the chance of one out of two engines failing is 4.75% in a twin versus 5% in a single. You're chances of a single engine failure actually go down in a twin.

Redundant systems don't increase the chance something will go wrong, however removing systems does decrease the chance they will fail ;)
Click to expand...

I hated stats. Walk us through the math on this one. I'm missing something. Not doubting....just confused. Where does the .95 come from? Is that the reliability of number two? (95% reliability of both.). :confused:
 
Baron2PG said:
Well, that isn't true either...sorry. Once you have a few hundred hours under your belt the insurance cost basically is a function of the hull cost plus liability. No different than a single...
Click to expand...

Odd, every time I've called about insurance on a Twinkie, it's been double that of my Comanche. I guess I really *don't* know my ass from a hole in the ground.
 
LDJones said:
I hated stats. Walk us through the math on this one. I'm missing something. Not doubting....just confused. Where does the .95 come from? Is that the reliability of number two? (95% reliability of both.). :confused:
Click to expand...

He did the math wrong. If you extrapolate his numbers out, if you have an infinite number of engines the chance of having a failure is 0. Which is completely backward logic.
 
EdFred said:
Odd, every time I've called about insurance on a Twinkie, it's been double that of my Comanche. I guess I really *don't* know my ass from a hole in the ground.
Click to expand...
It could be that insurance companies don't like Twinkies? :dunno: .....I only tried to quote for a Twinkie once and that was back when twin insurance in general was ridiculous....they told me they wouldn't even cover me period.....but that was 6 or 7 years ago.

You can find alot of difference in insurance between different makes and models within the same category/class.

Also, how many hours do you have in your Comanche and how many do you have in Twinkies? That can make a big difference in how the quotes compare vs a guy with no time in either models trying to get a first time quote.
 
EdFred said:
Odd, every time I've called about insurance on a Twinkie, it's been double that of my Comanche. I guess I really *don't* know my ass from a hole in the ground.
Click to expand...

How much Multi time you have vs Total Time? That has an effect on your first year/100hr's worth of insurance, but that's the only bill you are looking at. Once you put a 100hrs in the plane preferably in the first year, your insurance rate will be on the order of around 1.5% of insured value, same as everything else.
 
Fearless Tower said:
It could be that insurance companies don't like Twinkies? :dunno: .....I only tried to quote for a Twinkie once and that was back when twin insurance in general was ridiculous....they told me they wouldn't even cover me period.....but that was 6 or 7 years ago.

You can find alot of difference in insurance between different makes and models within the same category/class.
Click to expand...

Well considering I have the single version, you don't get any closer on comparison.
 
Henning said:
How much Multi time you have vs Total Time? That has an effect on your first year/100hr's worth of insurance, but that's the only bill you are looking at. Once you put a 100hrs in the plane preferably in the first year, your insurance rate will be on the order of around 1.5% of insured value, same as everything else.
Click to expand...

I asked them what my numbers were at 100, 250 hours ME. I don't recall off hand but they were still quite a but higher. More than 50% even with 250ME and the same hull value.

And I don't get where the 1.5% comes from. I'm at 3% on my single, with no more discounts coming. Avemco was still double what I am now with almost 1000 hours and 300+ in this plane.
 
LDJones said:
I hated stats. Walk us through the math on this one. I'm missing something. Not doubting....just confused. Where does the .95 come from? Is that the reliability of number two? (95% reliability of both.). :confused:
Click to expand...

.95, or 95% would be the chance the engine doesn't fail.

EdFred said:
He did the math wrong. If you extrapolate his numbers out, if you have an infinite number of engines the chance of having a failure is 0. Which is completely backward logic.
Click to expand...

What did I miss, you may be right, I've not taken a stats class in quite a few years. Although I believe my point is still correct.
 
EdFred said:
I asked them what my numbers were at 100, 250 hours ME. I don't recall off hand but they were still quite a but higher. More than 50% even with 250ME and the same hull value.
Click to expand...

Find a different insurance man or a better twin, Twinkie is kinda lame, might be why the insurance is high on it. Quick question though, is the Comanche you are in insured as 4 seat or 6, that makes a huge difference.
 
EdFred said:
Well considering I have the single version, you don't get any closer on comparison.
Click to expand...
That's just it. You already have a ton of time in the single Comanche. I totally believe you that the Twinkie quote would be much higher....because your single premium is probably fairly low.

But, if I (who has zero time in a single Comanche, but 150 ME plus 17 in the PA30) tried to quote both, I suspect that difference between the two quotes would not be as significant.
 
guardrail said:
.95, or 95% would be the chance the engine doesn't fail.


What did I miss, you may be right, I've not taken a stats class in quite a few years. Although I believe my point is still correct.
Click to expand...

No. It's not. Using your math, if I had 100 engines with a .95 success rate the chance of having a single engine failure is 0.59%. But it's really 99.4%.

It's not double, but it's close. 9.75% chance of an engine failure.
 
Fearless Tower said:
That's just it. You already have a ton of time in the single Comanche. I totally believe you that the Twinkie quote would be much higher....because your single premium is probably fairly low.

But, if I (who has zero time in a single Comanche, but 150 ME plus 17 in the PA30) tried to quote both, I suspect that difference between the two quotes would not be as significant.
Click to expand...


Oddly enough I have to call to get my insurance renewed soon. So I will ask again.
 
Henning said:
Find a different insurance man or a better twin, Twinkie is kinda lame, might be why the insurance is high on it. Quick question though, is the Comanche you are in insured as 4 seat or 6, that makes a huge difference.
Click to expand...

Insured as 4 seats.
 
EdFred said:
Insured as 4 seats.
Click to expand...

There's the biggest part of the difference likely, the Twinkie I believe quotes as a six seater, when you call the insurance man ask him if it's quotable as a 4 seat.
 
EdFred said:
No. It's not. Using your math, if I had 100 engines with a .95 success rate the chance of having a single engine failure is 0.59%. But it's really 99.4%.

It's not double, but it's close. 9.75% chance of an engine failure.
Click to expand...

Aha, yes you are correct. Should have googled first... (.05)+(.05)-(.05*.05)=.0975

I stand corrected!
 
EdFred said:
No. It's not. Using your math, if I had 100 engines with a .95 success rate the chance of having a single engine failure is 0.59%. But it's really 99.4%.
Click to expand...

But on the plus side, when you lose one, you hardly even notice it!! :goofy: :rofl:
 
We're paying about 1.5% on hull value for the 310, 2.2% for hull + liability. Avemco has crappy twin rates, so I wouldn't talk to them. Talk to a broker who knows the market better.
 
You must log in or register to reply here.
Back
Top