Why Twins Aren't Safer than Singles

[N747JB]

I cannot speak to others but it has been my experience that as a percentage twin owners are more apt to want to defer engine maintenance than a single engine owner. I have heard the words "It doesn't matter, have a spare engine" more than once.

Back to human factors

That is why you can't afford to buy a cheap twin!
I've had several people call on my 421 and they are all looking for a good, cheap, reliable 421 at the price as the neglected one that has been sitting on the ramp for years. Lots of people get twins at a good price compared to their capabilities, but even good ones cost money to maintain. Buying a 421 for $125K that will haul 2200 lbs, and cruise at 190-200 knots is pretty cheap, but it costs a lot of money to fly it.
I fly twins, because I like the space, speed and pressurization of a cabin class Cessna and I can afford to maintain it in top notch condition. That doesn't mean things don't break, just that I try to stay ahead of it and don't defer maintenance items.
Bottom line, fly what you like and what you can comfortably afford.

 

[Henning]

That is why you can't afford to buy a cheap twin!
I've had several people call on my 421 and they are all looking for a good, cheap, reliable 421 at the price as the neglected one that has been sitting on the ramp for years. Lots of people get twins at a good price compared to their capabilities, but even good ones cost money to maintain. Buying a 421 for $125K that will haul 2200 lbs, and cruise at 190-200 knots is pretty cheap, but it costs a lot of money to fly it.
I fly twins, because I like the space, speed and pressurization of a cabin class Cessna and I can afford to maintain it in top notch condition. That doesn't mean things don't break, just that I try to stay ahead of it and don't defer maintenance items.
Bottom line, fly what you like and what you can comfortably afford.

Exactly, you want good equipment, you can't have it for junkyard prices, that's all people want to pay at the moment. Problem is if you buy at junkyard prices you're gonna be spending considerably more shortly down the line than if you just bought in good condition to begin with.

 

[poadeleted21]

Exactly, you want good equipment, you can't have it for junkyard prices, that's all people want to pay at the moment. Problem is if you buy at junkyard prices you're gonna be spending considerably more shortly down the line than if you just bought in good condition to begin with.

IMHO, the market is efficient at assigning values, if it hasn't sold in 90 days... it's overpriced or an oddball with an extremely small market. It's not that buyers are cheap and sellers are the sane ones. Most buyers shop around and find the best deal.

 

[wabower]

Since you mentioned it, I'd think $125k is way too cheap for a nice plane like yours, and wouldn't consider a dime less than 130.

Glad to hear you made a deal. And even gladder that I'm not in the least bit tempted to do the same. "Free at last, free at last . . ."

Oh, and since we're talking about 421B's, the super-duper low-priced bird the guy bought for $150k (with no pre-buy) is about ready to leave the shop after about 6 months and roughly another purchase-price-worth of repairs. Your plane is a steal by comparison.

That is why you can't afford to buy a cheap twin!
I've had several people call on my 421 and they are all looking for a good, cheap, reliable 421 at the price as the neglected one that has been sitting on the ramp for years. Lots of people get twins at a good price compared to their capabilities, but even good ones cost money to maintain. Buying a 421 for $125K that will haul 2200 lbs, and cruise at 190-200 knots is pretty cheap, but it costs a lot of money to fly it.
I fly twins, because I like the space, speed and pressurization of a cabin class Cessna and I can afford to maintain it in top notch condition. That doesn't mean things don't break, just that I try to stay ahead of it and don't defer maintenance items.
Bottom line, fly what you like and what you can comfortably afford.

 

[Fearless Tower]

the super-duper low-priced bird the guy bought for $150k (with no pre-buy) is about ready to leave the shop after about 6 months and roughly another purchase-price-worth of repairs. Your plane is a steal by comparison.

Really??

Who does that? (buy an airplane that expensive without a thorough pre-buy).

 

[rcpilot]

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

You have it backwards. More systems increases the chance that a single one will fail.

I think what you actually want is .95*.95 = .9025 = chance of no failures occurring with two engines that individually have a 5% change of failure over the same time period.

It doesn't quite double, but it's close. You will never have a lower chance of engine failure with more engines. The benefit is that you have much less chance of all engines failing.

 

[N747JB]

Really??

Who does that? (buy an airplane that expensive without a thorough pre-buy).

You'd be surprised! There was a guy in town that bought a nice 421C, with a fresh annual and overhauled engines. The "overhauled" engines were just reprinted engines! The tail section was full of sheet metal screws instead of rivets! I don't remember what happened, he tried to sue the seller, but I think it was 4-5 months after he bought it when it came into the shop and all this fun was discovered!!

 

[EdFred]

You have it backwards. More systems increases the chance that a single one will fail.

I think what you actually want is .95*.95 = .9025 = chance of no failures occurring with two engines that individually have a 5% change of failure over the same time period.

It doesn't quite double, but it's close. You will never have a lower chance of engine failure with more engines. The benefit is that you have much less chance of all engines failing.

You're about 21 hours slow in your response.

 

[wabower]

At least six cabin-class twins that I can recall, usually older ones, although two of them were known to be re-build jobs prior to purchase. A pre-buy would have revealed that the extent of the rebuild was much higher than the estimates provided by the seller, but that's another subject. The flyable planes have typically been spiffed with a new interior (but with cheap material and poor quality workmanship) so they look good compared to the others. When one shows up under these circumstances, I normally assume the cost will double before the buyer ever logs the first hour. When the pressurization cart is hooked up and the soapy water is applied to the windows, the planes look like a front-load washer with too much soap. Then it's down-hill from there.

Really??

Who does that? (buy an airplane that expensive without a thorough pre-buy).

 

[LDJones]

When the pressurization cart is hooked up and the soapy water is applied to the windows, the planes look like a front-load washer with too much soap. Then it's down-hill from there.

Never seen that but I bet it's fun to watch! (Unless you're the new owner. )

 

[wabower]

It's pretty obvious that a high percentage of shops don't have pressure carts, or if they do they don't use them. As a result, their ability to check for cracked windows, bad ducts, door and window seals and other pressurization problems is limited. Nobody should buy a pressurized airplane without seeing it (and hearing it) when hooked to a cart. The whistling noises around the doors, including the emer exit, and windows rival the opening scene in an Andy Griffith segment.

And BTW, the emer pressurization valve on most twins hasn't been checked since the flood. And you can figure that all the known gear problems, exhaust problems, flap corrosion problems, nose compartment corrosion problems around the hot air supply duct, corrosion around the nacelle tanks, loose rivets and corrosion in the horizontal and vertical tail, torn up emer exit structure from trying to reinstall it with a flat-blade screwdriver, worn-out hardware on the air-stair door and a few other little things might surface as well. Nothing that $150k and 4-6 months won't make right

Never seen that but I bet it's fun to watch! (Unless you're the new owner. )

 

[Ted]

Never seen that but I bet it's fun to watch! (Unless you're the new owner. )

Probably pretty common, too. Local at my last airport bought a shiny RAM 340 cheap. Thing couldn't do close to max dif and clearly leaked pretty badly. A couple new windshields later fixed the problem, which wasn't a cheap job.

Then it had some weird running issue, which finally lead to a completely dead cylinder after 50 hours of running with a weird vibration caused by some broken valve springs.

But the P&I were really nice.

 

[LDJones]

But the P&I were really nice.

Sounds like they had lots of opportunity to admire the P&I with all the time it spent in the shop! :wink2:

 

[wabower]

Oh BTW, none of the de-ice valves will work either.

 

[Ted]

Sounds like they had lots of opportunity to admire the P&I with all the time it spent in the shop! :wink2:

Negative - work was done in a shop at a different airport!

 

[Skylane81E]

Oh BTW, none of the de-ice valves will work either.

If it wasn't so sad it would be funny

Ok ok

http://youtu.be/5A9SWgJOTL4

 

[sailbv@gmail.com]

That's why would need to have Xavion installed. No thinking about missing whatever available runway is around--simply shoot the hoops! And it works with iLEVIL (AHRS, ADS-B weather and traffic), just so you know..

 

[stratobee]

This age old debate has been raging forever and I have very little to add to it except my personal three main reasons for owning a twin:

1. I live in LA and most of my flying is xcountry. That means crossing the Sierra Nevadas and the Rockies pretty much everywhere I need to go. Sure, my old Commander won't keep altitude much higher than 7000ft, so that won't help me cross peaks at 12000ft. But it will drag me down to the ground a lot slower than a dead single, that's for sure.

2. VFR on top. Just the other day I flew back from Vancouver, and around Mt Shasta in Oregon the fog was to the ground. I flew more than an hour above a thick layer of fog that had left me zero options in a single. However, I would never do this over mountains or where I couldn't keep altitude above it.

3. Flying LA at night. Sprawling city lights everywhere and I simply don't know how the single engine guys can stomach it, yet they're doing it all the time. If it quits, you're looking at the 10 freeway in rush hour and that's about it. There are no other options.

I've had one partial engine failure, but she made enough power for me to continue the flight to my destination. Non event.

 

[wabower]

And if your fuel line breaks like mine did you're just as screwed as I was, that is unless you're as lucky as I was to have Bryce Canyon airport at 12 o'clock and within gliding distance. If engine failures were in fact the primary problem to be concerned about, the freeways would be littered with airplanes and the twins would be accident free.

This age old debate has been raging forever and I have very little to add to it except my personal three main reasons for owning a twin:

1. I live in LA and most of my flying is xcountry. That means crossing the Sierra Nevadas and the Rockies pretty much everywhere I need to go. Sure, my old Commander won't keep altitude much higher than 7000ft, so that won't help me cross peaks at 12000ft. But it will drag me down to the ground a lot slower than a dead single, that's for sure.

2. VFR on top. Just the other day I flew back from Vancouver, and around Mt Shasta in Oregon the fog was to the ground. I flew more than an hour above a thick layer of fog that had left me zero options in a single. However, I would never do this over mountains or where I couldn't keep altitude above it.

3. Flying LA at night. Sprawling city lights everywhere and I simply don't know how the single engine guys can stomach it, yet they're doing it all the time. If it quits, you're looking at the 10 freeway in rush hour and that's about it. There are no other options.

I've had one partial engine failure, but she made enough power for me to continue the flight to my destination. Non event.

 

[zaitcev]

3. Flying LA at night. Sprawling city lights everywhere and I simply don't know how the single engine guys can stomach it, yet they're doing it all the time. If it quits, you're looking at the 10 freeway in rush hour and that's about it. There are no other options.

If something happens, they just aim roughly to a baseball diamond and pull the chute.

 

[Dave Siciliano]

That didn't work to well on the one where the chute didn't deploy last week.

Best,

Dave

 

[TriGear28]

Of course the twin is safer. It stays in the only place I can afford to take it... The ground!

 

[spiderweb]

My reckoning is simple: if you have two powerplants, and one goes, you still have something making some power. Yeah, yeah, you have to be adept at handling a failure, but isn't that obvious?

Safety is up to YOU.

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.

 

[azure]

I hate to chime in on threads like this since I always feel like I'm jinxing myself, but complete engine failure in a single is a rare enough event that most single drivers will never experience one. Engine failure is NOT a major reason for GA's dismal safety record, we have a long way to go on cleaning up our act before we'd need to worry about that.

Notwithstanding, if fuel was still under $3 I would probably think more seriously about flying a twin. As it stands, it's far enough beyond my means that I'm not even considering getting my AMEL.

 

[Ted]

I hate to chime in on threads like this since I always feel like I'm jinxing myself, but complete engine failure in a single is a rare enough event that most single drivers will never experience one. Engine failure is NOT a major reason for GA's dismal safety record, we have a long way to go on cleaning up our act before we'd need to worry about that.

Notwithstanding, if fuel was still under $3 I would probably think more seriously about flying a twin. As it stands, it's far enough beyond my means that I'm not even considering getting my AMEL.

While you're correct that we as an industry have a long way to go, for those who are capable and competent in OEI operations a twin does have extra safety benefits. So basically everyone who buys a twin thinks they're in that category of being benefitted by having two instead of one. Some of them are right, some are not. And some of them run out of fuel.

 

[Dave Siciliano]

My partner lost the left engine in our P baron last Fall at 17,000 feet IMC. Caged it, diverted to the nearest reasonable field (he had several choices where he was between altitude and remaining engine power). Non-event other than some material from his seat that was sucked up onto the back of his pants (g). I leaned more to the twin when I started doing longer trips at higher altitudes where there were always changing weather conditions. Over mountains, water, low IMC and night operations led me to the twin. Never lost an engine when single engine, but knew several folks that lost one. Yes, a lot of pilot error, but with family, in the conditions mentioned, I wanted all the redundancy I could afford.

Departed BJC last February in blowing snow with low ceilings and vis of 1/2 mile. Tops were at FL230 and there was some icing in the climb. Great time to be in a King Air. Wouldn't have gone in a single and probably not in the P baron.

Best,

Dave

 

[wabower]

Well, there are Twins and then there are TWINS! Moving to turbines is a whole new game in terms of capability and de-pucker, especially for guys like you who work hard at maintaining proficiency.

My partner lost the left engine in our P baron last Fall at 17,000 feet IMC. Caged it, diverted to the nearest reasonable field (he had several choices where he was between altitude and remaining engine power). Non-event other than some material from his seat that was sucked up onto the back of his pants (g). I leaned more to the twin when I started doing longer trips at higher altitudes where there were always changing weather conditions. Over mountains, water, low IMC and night operations led me to the twin. Never lost an engine when single engine, but knew several folks that lost one. Yes, a lot of pilot error, but with family, in the conditions mentioned, I wanted all the redundancy I could afford.

Departed BJC last February in blowing snow with low ceilings and vis of 1/2 mile. Tops were at FL230 and there was some icing in the climb. Great time to be in a King Air. Wouldn't have gone in a single and probably not in the P baron.

Best,

Dave

 

[Ted]

Well, there are Twins and then there are TWINS! Moving to turbines is a whole new game in terms of capability and de-pucker, especially for guys like you who work hard at maintaining proficiency.

In toying around in my head about how I'd design a theoretical experimental twin, the basic technical requirement would be to get performance and simplicity of use akin to what you find in the turbine world. I think the main reason we haven't seen it is that piston twins stopped getting produced around the time systems finally got to the point where they could technically support such quirements. And then we haven't seen the systems produced since due to the general lack of money in GA making the required R&D impractical.

 

[Skylane81E]

So enlarge a v twin suffiently for two turbo Diesel engines and add pressurization. Seems you could then get a pressurized jet-a burner that would haul 6 people with rather generous performace

 

[Ted]

So enlarge a v twin suffiently for two turbo Diesel engines and add pressurization. Seems you could then get a pressurized jet-a burner that would haul 6 people with rather generous performace

That's one way of doing it, but I think my version would look more like a 310 with 421 wings and that DuraMax powerplant we were talking about a few months back.

 

[Skylane81E]

Need to find funding for that project

 

[hindsight2020]

And that's the great ol' elephant in the room that everybody keeps ingoring in these discussions. Piston twins are not real multi-engine aircraft. The residual performance on one engine is so paltry due to the small power output per engine that for the purposes of go/no-go on take off/MGW go-around decisions they are de facto single engine aircraft. When your V1~Vr+X, your twin is not a real multi-engine aircraft and does not meet the spirit of powerplant redundancy.

People should think of sub-600HP piston twins as single engine aircraft with a trolling motor for getting over non-gliding distance bodies of water at 3000' AGL or below. The merit of splitting the source of power among two sources in most piston twins is overstated for the rest of mission sets, particularly with terrain at altitude. The only scenario where these trolling boat multis make sense, is over-water missions.

 

[Skylane81E]

Or in cases where you need more than about 350 HP as that is about the practical limit of a modern direct drive piston engine.

 

[Ted]

Need to find funding for that project

That's why I haven't done it yet.

 

[Ted]

And that's the great ol' elephant in the room that everybody keeps ingoring in these discussions. Piston twins are not real multi-engine aircraft. The residual performance on one engine is so paltry due to the small power output per engine that for the purposes of go/no-go on take off/MGW go-around decisions they are de facto single engine aircraft. When your V1~Vr+X, your twin is not a real multi-engine aircraft and does not meet the spirit of powerplant redundancy.

People should think of sub-600HP piston twins as single engine aircraft with a trolling motor for getting over non-gliding distance bodies of water at 3000' AGL or below. The merit of splitting the source of power among two sources in most piston twins is overstated for the rest of mission sets, particularly with terrain at altitude. The only scenario where these trolling boat multis make sense, is over-water missions.

They have two engines, so they're real multi-engine aircraft. It's no secret that the performance limitations are real and do exist - I think the twin owners on here discuss them all the time, so it's hardly an elephant. Respect those limitations and you can still see a safety benefit and not be limited to safer over water crossings.

I guess transport category jets aren't real, either? After all, an F-15 I'm sure has better OEI.

 

[Morne]

The only scenario where these trolling boat multis make sense, is over-water missions.

You ever fly over West Virginia? The terrain isn't that high, especially compared to the rocks out west, but you don't want to do a forced landing on it all the same.

 

[wabower]

Why do the twin fan-boys always default to an engine loss scenario when they are so infrequent and OEI crashes are so frequent?

You ever fly over West Virginia? The terrain isn't that high, especially compared to the rocks out west, but you don't want to do a forced landing on it all the same.

 

[Ted]

Why do the twin fan-boys always default to an engine loss scenario when they are so infrequent and OEI crashes are so frequent?

Do you have statistics on engine failures with successful landings? That's the part that I've been looking for.

 

[Dave Siciliano]

Ted: As you know, they needn't be reported. FSDO did call us after our engine failure because ATC reported it as an emergency even though my partner didn't declare. When I explained what happened, they just did a brief report and closed the file. Did ask if we were suspicious of engine work done or any work on the plane. We said no. I told FSDO it's why we flew a twin and did recurrent training. Did what we trained and it was a non-even from the damage/injury perspective. He just chuckled and said, yes, that's what's supposed to happen. New engine being broken in with reputable provider. Most don't report at all. Some are precautionary shut down for things like a chip detector light or other unusual indication/condition. The shut down is to preserve the misbehaving engine. Don't have that luxury with a single often. I'd keep it running if it could make a difference even if more engine damage occurred; whereas, in the twin, I can shut one down and still go a long way in all but the highest terrain. In my plane, just under max gross 14,000 on ISA +37 day (only chart I have).

Best,

Dave

 

[bbchien]

Post #52 from hindsight2020, is only true if the PIC does not recognize the imporance of Gross weight for THIS OPERATION TODAY, and the circumstances TODAY.

It is all about weight management. If one loads a part 23 AC to the marketing director's legal limits, you will get 220 FPM climb, and will need 6,000 feet at STP at Zero MSL to get it to Vyse and stopped. And if you load up a Howard 500 to book gross, that's about what you'll get....and that has WAY more than 600 hp.

All that dramatically changes at 5% undergross. Go/fail/flyaway occurs commonly at 3,100 feet (in mine) and I can clear the 37 feet tall apartments 1600 yards away. Go/fail/stop shrinks to 4000 feet under most summer conditions at 300 undergross in my 4570 lb aircraft. 7% is a lot undergross. You have to constantly consult the engineering dept's tables, not the marketing dept's.

So, the real reason why MEI flight is not safer than SE flight is that, like Cirrus pilots, ME-pilots are not necessarily the sharpest tools in the shed. You need to know your go/stop and go/fly-away distances, do the calculation as to your clearway climb gradient, just like we do when we're flying "big boy" aircraft". You cannot kick the tares and light the fires. Both types of a/c penalize the farmer who drives his new ultra stable tractor, farther up the hill on the back 40. Witness the St.Ignace Baron crash'nburn about three years back. Both fans were turning.

I don't buy the argument that part 23 AFMs don't have the required information. Wayy back when I was on engines #5 and 6 ago, I blew those runouts HARD on a 10,000 foot runway, wore out a trio of tires, breaks and rotors essentially creating a spreadsheed of the critical distances according to wind, temp and baro. Then I reman'd both engines. You gotta know; GET the information. Not being handed the information is NO EXCUSE.

I do not sign off any ME pilot who fails to verbalize the pre-departure briefing.