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Anyone interested in twin GA flying: a GREAT article

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...and a good document to compare the engine-out performance of sim twins:-http://www.cyberair.com/tower/faa/app/p8740-25/p8740-25.htmlHere's the start:-While single-engine aircraft may not be safer, twins can be more dangerous/Richard N. AaronsDESPITE heated scoldings from flight instructors and grim warnings from the National Transportation Safety Board, many pilots still seem to believe that implied in the fact that an aircraft has two engines is a promise that it will perform with only one of those engines operative. And the light-twin stall/spin accident rate further indicates that many multi-engine pilots have not come to grips with the facts that: * Significantly more than half the climb performance disappears when one engine signs out * Exploration of the Vmc regime close to the ground is a sure way to kill yourself.Sobering stuff.

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IN fact the FAA certification for a twin engine prop a/c in the US does not require that it have climb capability on one engine, only that you can maintain directional control with the good engine at full power.In other words, it is only guaranteed to get you to the scene of the crash.

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Yep, twins have two engines because they NEED them. If you're not proficient then you're much better off in a single. But if you know your machine then the extra engine will at least buy you some options. You also have the benefit of redundant systems - electrical, pneumatic, hydraulic, vacuum - so you're also more likely to consistently make it to your destination without the failure of a critical system.Also keep in mind that the published figures are at MGW so (assuming lighter weights on a typical mission) performance may be somewhat improved from what is shown.Pop quiz: what happens to VMc as operating weight increases?

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>Pop quiz: what happens to VMc as operating weight >increases? Vmc has an inverse relationship to weight.Weight goes up -> Vmc goes downWeight goes down (fuel burn for instance) -> Vmc goes up.As far as I understand it, this is to do with the decreased inertia at lower weights and the increased inertia at higher weights.

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Inertia would only affect the RATE at which yaw occurs, but not the speed at which directional control is lost.However, you answer is correct.VMc is defined by a very strict set of conditions:(1) Max available power(2) Most unfavorable CG.(3) Max t/o weight.(4) Flaps in t/o position.(5) Gear up.(6) Windmilling prop on dead engine.(7) Outside of ground effect.(8) Up to 5^ bank into good engine.The inverse relationship has to do with (8). The 5^ of bank produces a horizontal component of lift which helps to counteract the yaw toward the dead engine. At higher weights, this component is greater resulting in more availabe control and a lower VMc.However, this is not meant to imply that higher weights are safer when operation with one foot dead. For one thing Vs increases with weight. You may find a situation where Vs becomes higher than Vmc. This is not to mention the decrease in climb rate.

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I place the blame for the high accident rate in twins down to incorrect training in light twins.Most of the training involves engine failure after takeoff in the climb and how to setup a climb to circuit height.Most light twins dont do a good job in this area and if the pilots arent as sharp as razors your looking at a stall spin situation.I have now had three engine failures in twins, one at fifty feet after takeoff in a Baron B55, one at 200 feet in the climbout in a Seneca 4, and one in the cruise in a Seneca five.The engine failed at 200 feet in one of the above but was still producing about 30% power, I went against training and kept the thing going with my hand on the prop lever until I had climbed to 1000 feet as at grosse weight and the oat I knew I would go down if I had feathered the prop and shut down at that height.We are taught to handle an engine failure as if we were in a turboprop but this is a bad mistake.Most twins will fly happily in the cruise on one engine.Infact on my initial conversion to Senecas we shut an engine down and flew all the way to France restarting it for a landing.This was a crazy thing to do but ???? :-)At most airfields it is quite in order to do a circuit at 300 feet 400 feet 500 feet.Maybe the procedure should be to establish level flight and forget an attempt at climbing. Once all is stable with the prop feathered then do a leisurely turn and a low level circuit to land, or climb with the trim wheel at maybe 50-100 fpm but with plenty of speed until you hit a safe altitude even if this takes 20 miles.If there is terrain around the airfield chances are you wont outclimb on one engine anyway.I blame the training which is not suitable for light twins but is suitable for aircraft which climb at more than 500 fpm on one engine.Peter

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Keeping current in 'engine out' techniques must be very important in this. I've always found this article by Mike Busch about his 'proficiency training' on the professional simulators at 'Flight Safety'to be very interesting reading(http://www.avweb.com/articles/fsistory.html)I wonder what other experienced pilots of light twins (like Peter) think of the other pilot in the article Nick's technique of by passing the 'dead foot, dead engine' method and 'closing'the failed engine by reference to the yaw of the plane instead. it would be disaster to close the wrong one.Dave T

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>"I place the blame for the high accident rate in twins down to incorrect training in light twins."I agree with David; it's not incorrect training that causes the accident, but rather a lack of continued proficiency. If the training were incorrect then (hopefully) the check ride would be failed.And I believe that there is a subset of (at least) two types who fly twins - the professionals that train/fly daily and the "doctor" types who have enough money to afford a twin but have significant real-world obligations that prevent them from remaining current in the aircraft. This is an (unfair) overgeneralization, but it happens again and again - and the effects are not limited just to twins.

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DennisTraining or no training some very light twins in certain circumstances/weight/temp will not climb on one engine regardless of the brilliance of the pilot.Remember too that the quoted figures are taken on new aircraft not 20 year old aircraft with nearly time expired engines and a good dose of hanger rash to boot.I like to think of the other engine as giving you more options one which "might" be to climb if you loose an engine at 300 feet on the climbout.When I had my angine failure at 200 feet I could have followed published procedures and feathered the engine.Because of the temp and weight and my instincts that the aircraft was not going to climb with the engine shut down and realising that it was still producing "some" power I elected to use that some power with my hand on the prop lever ready to pull it back if the unit went big time.Once I had a reasonable amount of air below the plane I then shut the engine down.Training is ok if your looking at aircraft which will climb at more than 500 fpm but to purely drum those procedures into a pilots head in very light twins is asking for the stall/spin accidents that occur.Yes I agree that currency is important but thats not the whole picture.Peter

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Peter,I understand your perspective, but I respectfully disagree.In broad, general terms, there are really just two scenarios for an engine failure in flight: above and below the safety altitude. If the failure occurs below that point then the most prudent (and best odds) method is to secure the engine and return for landing. If the failure occurs above that point then you should troubleshoot prior to securing.Any engine failure goes through these steps:Airspeed!Mixture forwardProps forwardThrottles forwardFlaps upGear upIdentifyVerifyFix (or Feather)Airspeed!In your scenario, you would have detected the residual thrust at the "verify" step - by noticing an increase in yaw when the failed throttle was retarded. Proper training would not have you continue to secure this engine under that situation.I'm probably not understanding your post correctly, but to suggest that a completely failed engine should not be secured immediately at 200' is suicide. Feather and blue-line are your only concerns at that point; it is way to easy to lose your primary objective - flying the airplane - when you're troubleshooting that close to the ground. If you're concerned about a stall/spin then you definitely don't want the pilot's head looking around for the source of a failed engine. The windmilling prop will cost you 200 (or so) fpm of climb so at low altitudes there really is not other choice but to feather it immediately upon verification. I don't see where the performance capability of the aircraft would affect my progression through the above steps. Even if I were in an old Apache that, under the best conditions, will descend 100 fpm with one fan spinning, I would still follow the above. The only difference there is that I may be looking for an off-airport landing site rather than working to complete the pattern.My point here is that your training was correct and served you well.

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>I'm probably not understanding your post correctly, but to suggest that a completely failed engine should not be secured immediately at 200' is suicide.

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>"What I am suggesting is that the training to establish blue line speed and a climb in all cases of a failed engine at low altitide isnt always the best route and that training has lead to many stall/spin accidents in light twins."How in the world can blue-line induce a spin? For a "failed engine at low altitude" this is the ONLY correct speed. I have never seen an aircraft that had blue line lower than either Vmc or Vs. If you are suggesting that pilots who lack proficiency risk sinking below Vyse then I agree. But lack of proficiency is an entirely different discussion than teaching anything other than pitching and trimming for blue-line immediately upon a low altitude engine failure. Pilots who lack proficiency do a lot of other dumb things but we still teach them the correct procedures from the start.>"Neither is taking to the nearest field with an aircraft which wont climb but will happily fly level on one engine (why go down when you dont have to?)"Well, you have to come down eventually. I don't know what direction you're going with this but the continuance of a flight with one engine shut down is completely unsafe. No matter how inconvenient, landing at the nearest suitable airport is nearly always the best course of action. Do you know what caused the engine failure? Was it something in the fuel that may affect the other engine before long? Did the mechanic make the same mistake on both engines? Did the fueler leave both oil or fuel caps off? Is today not your lucky day? What possible safety benefit is there in extending the trip beyond the nearest suitable airport?>"Instead of mainting blue line speed and a climb when the donkey goes bang at 300 or 400 feet why not just push the nose over establish level flight with more than blue line speed at the 300- 400 feet and then either bleed on altitude maybe at 50 fpm using the sensitive trim wheel or do a gentle turn and low level circuit back to a landing.You must be kidding! What possible advantage is there in flying faster than blue-line. The extra airspeed buys you nothing. Any altitude gained (or prevented from being lost) by maintaining blue-line buys you options.>"People are taught twin flying as if they were flying a B200 turboprop not a tiny twin and there are other options rather than the do or die establish blue line and a climb which has caused a lot of stall/spin accidents even to proficient pilots."Again, I have no idea how a proficient pilot could spin any twin at blue line. I teach people to fly twins as recommended by the FAA and the POH. The manufactures paint red and blue lines on the airspeed indicator because of their importance.>"This theory was put to me by a test pilot/fighter pilot who also flew light twins and couldnt understand the madness of the blue line climb at all costs training in twins which will fly forever level on one engine but wont "always" climb on one."Twins will forever have better vertical performance at blue-line than at any other speed. If you're at several thousand feet enroute than I agree, there is no need to immediately go to Vyse, but this discussion has to do with failure at low altitudes.

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DennisYou are presuming a lot with the idea of flying blue line speed and a climb at low altitude.In an ideal world yes you will have a brand spanking new twin, with standard day temperatures, be at an airfield which is at sea level or thereabouts and will be proficient enough to coax a climb of 200 fpm or less.Im afraid this isnt an ideal world. Yes the poor pilot who doesnt meet the above criteria will try and maintain bue line speed but remember there is another factor which comes into play "induced drag" sinking pockets of air or any other factor including nerves which will see that blue line speed vanish.Now the pilot is faced with a crossed up aircraft and falling speed.He adds more rudder to compensate for the lower airsped and more aeleron which itself adds more drag and hence even lower speeds and hey presto the guy is down at VMCA and quickly loosing the plot.I repeat most light twins do a BAD job of climbing on one engine at grosse weight even in ideal conditions but do a good job of flying level.Why then add more danger by attempting a climb?I fly 300 hrs a year in twins and have experienced three engine failures, bar room chat wont prepare you for the real thing or for how easely that blue line speed vanishes.Yes speed is your saviour not getting into an induced drag situation.I still hold that twin engine training should look at other options other than the proverbial blue line and climb at all costs, this is one option but not the only one.The trouble in aviation is that nothing changes fast and old isnt always best.Peter

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DennisReading your post this morning i realise that either you are misunderstanding what I am saying or twisting my words to say what you want me to say for the sake of this arguement ;-)In no way am I disputing the principle of climbing at blue line speed.Hopefully if you have your engine failure at low level you will be below grosse weight and the OAT will be below standard day.Let me then ask you a question based around this scenario and how you as PIC would handle this situation........................You are flying an old Piper Seneca one, apache, Duchess or whatever your airfield elevation is 1800 feet ASL.You have loaded your passengers, luggage and fuel for a longish trip and have noted that the aircraft is right on grosse weight for the takeoff.You check the OAT and note it is 30 degrees C (IE 15 degrees above standard day)Infact probably a typical summertime temperature in many parts of the world when most people will be flying their friends and relatives around.The surrounding area is flat but quite heavely wooded with smallish fields and outcrops of rock.You takeoff, clean up the aircraft and as you are passing 300 feet AGL the engine goes bang big time......................What do you as PIC do????????????????????I am not in my arguement disputing the principles of blue line or procedures for identifying and shutting down a dead engine.What i am doing is acknowledging that the extra engine gives you more options and with those more options come more options for mistakes.You have three options One to establish blue line and attempt a climb Two to establish single engine cruise at low levelThree to pull both engines back, treat the aircraft as a single and make an off airport landing.In the above scenario I know which option I would take and it wouldnt be No 1.Light twins are special and have their own limitations which more powerful twins (turboprops)dont have.Training in them should explore the "other" options and not treat them as if they were powerful twin turboprops.Lets look at the science of this extra option. I am sure we are both in agreement that in the event of an engine failure we need to remove as much drag as possible.This drag is typically from gear, flaps, cowl flaps, props on the dead engine.By placing the aircraft in a climb we are infact then adding drag which we dont need or want.By pitching for a blue line climb we are increasing the angle of attack and hence induced drag.By mainting blue line we will require more rudder hanging out in the airstream and more aeleron than we would at higher speeds in a single engine level cruise so we have added three new levels of drag by pitching for a blue line climb which we dont need.You are happy to setup a level cruise at 7000 feet if the donkey goes bang but not at 300-400-500 feet.Infact the plane will fly better low level in the cruise on one engine than it will at 7000 feet due to airdensity.The aircraft doesnt know its at 300-400-500 feet only you do :-)Dennis I am not trying to point score with you as you are an instructor who follows training procedures which are well established and set in cement.I am purely questioning that training specific to very light twins and wondering whether the low level cruise shouldnt be taught and regarded as another option as well as establishing blue line and a climb.Peter

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Hi All,The original article cited is an excellent read and one we include in our multi-engine courses. A couple of points to add / reiterate as there seems to be many misconceptions about M/E ops.In any discussion of multi-engine theory and one engine inoperative (OEI) flight, it has to be made clear whether you are talking about an aircraft control issue (Vmc) or a performance issue (Vyse). Inevitably, multi-engine pilots will confuse themselves if they attempt to blend the two.With respect to maintaining aircraft (directional) control, we are talking about Vmc. What is good for improving control may be bad performance (weight is a perfect example, as previously pointed out).Much like stall speed, Vmc is a fluid number that changes with a variety of factors. The 7-8 factors Dennis mentioned are for aircraft certification purposes only, and usually have little relevance in real life (a manufacturer needs to paint the red radial somewhere on the airspeed indicator, and these are the conditions under which all manufacturers are governed). You know you have exceeded Vmc when you have full rudder deflection into the operating engine and can no longer maintain direction control (heading). Period. Forget the red line.Aircraft performance is all about Vyse (or Vxse in the case of obstacles). One pet peeve is pilots the use of the term "blue line". Blue line is the single-engine best rate of climb at a certain density altitude and weight (gross). Vyse is the computed best single engine rate of climb for your current conditions and should be computed before each takeoff from the performance charts. Actual Vyse may be substantially less than the "blue line" painted on the airspeed indicator which may make the difference between climbing or descending.Because Vyse is always above Vmc, Vmc is usually not too much of a concern in real life flying. Just like a stall, though, it is the distracted pilot who becomes a victim of a real Vmc encounter, which near the ground (just like the stall) is almost always fatal.Bottom line. When (if) you lose that engine after takeoff, picthing for and maintaining Vyse is the only way to go. Each knot above or below Vyse means reduced climb performance (by definition).Just my two cents...CaryCFIMEI

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>Bottom line. When (if) you lose that engine after takeoff, picthing for and maintaining Vyse is the only way to go. Each knot above or below Vyse means reduced climb performance (by definition).

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DennisFirstly I find this conversation very interesting so thanks for that.Vyse is not some magic figure that must be pegged in the event of an engine failure otherwise if you shut down an engine in the cruise you would then reduce your cruise to Vyse which is obviously nonsense.Vyse is only relevant to climbing an aircraft with one engine out.If conditions are such that you are infact flying level with no climb at Vyse then I suggest that the aircraft is on the back of the drag curve.Any pitch to climb the aircraft will change the angle of attack hence increasing induced drag and any sort of drag is the last thing you need.You need altitude so to get that altitude you are placing the aircraft in a negative tradeoff to achieve that altitude comnpared to the same aircraft trimmed for level flight.I can guarantee that after a single engine climb you will only relax once the aircraft is trimmed in the cruise and I know which feels better and which has less relevant drag.Taking the Seneca five are you suggesting that the aircraft will behave better at 89 kts Vyse than 120 kts single engine level cruise?I know your not.I feel the problem between us on this is divorcing a climbing aircraft or one thats attempting to climb from one in the cruise even if its a single engine level cruise, Vyse is only relevant to attempting a climb and not to a level cruise.All my arguement is about is that there are situations where you are better to forget futile attempts at a climb and go for a cruise instead.Otherwise why level off at all? At what height would you level 500 feet? 1000 feet 2000 feet? altitude is only relevant to terrain avoidance and having some air below the aircraft to trade off for speed if you need it.All the best and no hard feelings Peter

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