Performance for light twins
I don't have the stats to back it up, but anecdotaly it seems that the outcome of engine failure on a single engined aircraft is often better than for a light twin. Perhaps the the SOP for twins should be to take off on one engine and only fire up the second when safely in the cruise. And before I get flamed, yes I am joking.
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I suspect that the main reason for the twin-single paradox is the consequence of poor training ... many a light twin pilot tries to stay in the air when he ought not to .... too slow .... Vmca ... and it's all over ...
Maybe not poor training but lack of experience / infrequent practice. The problem with the twin is it gives the commander two options. The single only gives you one and it concentrates the mind beautifully. Even when it's still running sweetly, constantly at the back of one's mind "If it does, where..."
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light twins
Tinstaafl.......Well said.
How to survive a light twin public airservice job using several types of piston twins, small and bush type runways, and fatigue ?........perhaps this:-
Max Power.....all levers foward.
Climb............get that airspeed correct, FLY THE PLANE !
Flaps/cowls...get it correct
Gear............up...unless your world is paved !
Identiffy.......which one is duff ?????
Verify..........get it correct,retard the throttle
Feather....... FLY THE PLANE !
With luck, you'll fly it out straight ahead and gain a few hundred feet
before your good engine overheats.
Most times you'll fly it into a flat spot and tell them that you did all that you could do. Good luck. Extra good luck!!!!!
How to survive a light twin public airservice job using several types of piston twins, small and bush type runways, and fatigue ?........perhaps this:-
Max Power.....all levers foward.
Climb............get that airspeed correct, FLY THE PLANE !
Flaps/cowls...get it correct
Gear............up...unless your world is paved !
Identiffy.......which one is duff ?????
Verify..........get it correct,retard the throttle
Feather....... FLY THE PLANE !
With luck, you'll fly it out straight ahead and gain a few hundred feet
before your good engine overheats.
Most times you'll fly it into a flat spot and tell them that you did all that you could do. Good luck. Extra good luck!!!!!
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What works for me, teaching multi engine students and even those who want help:
Fly for blue line, straight ahead throughout the exercise
Everything UP (gear, flap)
Everything FORWARD (both sets of throttles, props and mixtures)
IDENTIFY (dead leg works best)
CONFIRM (throttle closed)
FEATHER
Mixture ICO
COWL FLAP closed.
Checklist if there is time.
Fly for blue line, straight ahead throughout the exercise
Everything UP (gear, flap)
Everything FORWARD (both sets of throttles, props and mixtures)
IDENTIFY (dead leg works best)
CONFIRM (throttle closed)
FEATHER
Mixture ICO
COWL FLAP closed.
Checklist if there is time.
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This theory about twins versus singles and statistics goes around and comes around...
It's down to reporting:
Engine failure in a single: very likely to be reported, quite likely to end with a happy outcome (low stall speeds, tend to fly in good weather, etc);
Engine failure in a twin: much less likely to be reported, because it usually ends with a landing at an airfield, usually (but not always) with a happy outcome, but when its an unhappy outcome it tends to be serious (higher stall speeds, energy proportional to V squared, they more often fly in bad weather, etc).
A piston twin in the hands of a well-trained and able pilot is a MUCH better option than a piston single...
It's down to reporting:
Engine failure in a single: very likely to be reported, quite likely to end with a happy outcome (low stall speeds, tend to fly in good weather, etc);
Engine failure in a twin: much less likely to be reported, because it usually ends with a landing at an airfield, usually (but not always) with a happy outcome, but when its an unhappy outcome it tends to be serious (higher stall speeds, energy proportional to V squared, they more often fly in bad weather, etc).
A piston twin in the hands of a well-trained and able pilot is a MUCH better option than a piston single...
Identiffy.......which one is duff ?????
Verify..........get it correct,retard the throttle
Feather....... FLY THE PLANE !
With luck, you'll fly it out straight ahead and gain a few hundred feet
before your good engine overheats.
Verify..........get it correct,retard the throttle
Feather....... FLY THE PLANE !
With luck, you'll fly it out straight ahead and gain a few hundred feet
before your good engine overheats.
Real life isn't that straightforward, is it? Even if you lose all but 20% of the power in a malfunctioning engine, that 20% might double the excess power available to give the aircraft a sensible airspeed and rate of climb. In an aircraft that is marginal on a single engine, that can make a huge difference to the likelihood of a safe outcome.
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And that is the "COMFIRM" part of the procedure. If you pull the throttle back to confirm your identification and you do not see a change in yaw, noise etc, you have a dead engine and have correctly identified it. Go ahead and feather the same engine. If you pull the throttle back and everything goes quiet, you have mis-identified the failure; put everything back where it was and pull the other throttle. If you pull the throttle and you get a small change, and further yaw, then you have a partial failure. In this case, you might choose to push the throttle back up and use that power to get to a safe altitude before going ahead with the shut down. In some engines, such as the PW 985 round engine, this could lead to catastrophic failure with a high risk of fire, but in most flat fours or sixes, the engine will run for a few minutes at least before seizing or falling apart. He says confidently.
It might not be a simple procedure, but that is why you get paid so much to be the pic.
It might not be a simple procedure, but that is why you get paid so much to be the pic.
SN3, you quoted the whole sentence but it appears you didn't read the whole sentence. There is a specific condition attached to the idea I presented of light twins not being a 'true' multi-engine a/c. I even used apostrophes to show that I wasn't using the word 'true' in the literal sense.
There certainly *is* a concept of a requirement for continued flight 1 inop for multi engine aircraft - and that's judged by more than one criterion. FAR25 & equivalents are all required to demonstrate the ability to reject or continue & thereafter fly to a suitable landing place. Even some Part 23 a/c have a similar requirement imposed ie Commuter Category.
Further, additional regulations in many jurisdictions force the requirement for some asymmetric ability depending on the type of operation, Australian & JAA Authorities, for example, forbid the use of single engine piston aircraft for IFR pax charter - because of the perceived safety of having a second engine in case one fails. I should add that the relatively recent approval in Australia to allow Single Engine Turbines to be used for IFR pax charter was based on them being able to demonstrate an equivalent level of safety from an engine failure perspective. There are operational limitations that light piston twins needn't observe that SET must do for an equivalent level of safety precisely because of the requirement for a certain amount of asymmetric performance.
Even the general public's belief is that the second engine provides continued flight capability. Which, by the way, is rather well reinforced with companies pervasive use of phrases such as 'twin engine safety' and the like. Admittedly the general public can't be considered to be knowledgeable in the field but the underlying expectation is still relevent. If it wasn't then we wouldn't have to spend so much time hammering into brand new light twin pilots just what that extra engine means when a donk stops (not much in the take-off or landing configuration other than profoundly degraded handling qualities in most cases).
Part 23 (non-commuter) types aren't absolved from meeting some asymmetric climb performance. But in these cases the conditions attached aren't nearly as comprehensive & the required level of climb performance ranges from poor to non-existant, perhaps only enough to fly to a better crash site. Compared to the other multi categories' required asymmetric performance they are the 'nearly there's'.
frontlefthamster, surely you're not suggesting that the a/c is not controllable at Vyse? What about at Vxse? I must disagree with your assertion that a speed margin above blue line is what provides the means to recognise & handle a failure. To say so would mean that any max performance take-off will automatically result in a Vmc departure following a failure. 'Blue line' as depicted on the ASI isn't even a fixed quantity except for a constrained set of conditions. It sounds like you're confusing Vmc (a controllability issue and itself variable from the certification figure) with Vyse (a performance issue) whilst ignoring Vxse at the same time. In that respect you're quite correct: You should not become airborne below Vmc because of the high probability of an uncontrolled crash.
Yaw, secondary roll, control inputs to stabilise the aircraft & gauge indications are the usual indications of failure - and they all occur at speeds above & below Vyse. To avoid flying at a best performance speed that is above Vmc because you believe that the speed buffer will give a better failure indication is not wise. You would look pretty foolish if an engine stops with obstacles still above you having squandered what limited energy you had prior to the failure.
Any competent & current pilot should be capaple of controlling a failure at blue line and should not need a buffer above blue line to control the aircraft. Not to be able to do so reflects poorly on the pilot's training &/or currency.
With respect to Asymmetric Commital Height, I'm familiar with the term as used in Europe. I don't think 500' is too high for it. Under adverse WAT conditions there can be a significant height loss until established in the climb. Don't know about you but even though I might be able to have the asymmetric beastie cleaned & climbing from 300' without hitting the ground , I strongly prefer not to put myself at ~100-200' (or less if things are *really unfavourable) going around on one engine with bugger all climb performance. I'd rather land beside/behind/ahead of the idiot that taxied onto the runway in front of an aircraft with a declared emergency.
And by the way, I suppose it is theoretical and my 25 years experience, over 20 of which has been flying a broad range of Part 23 twins including instructing & examining, counts for little. Even so, it's still the case that sound theory engenders good practice.
There certainly *is* a concept of a requirement for continued flight 1 inop for multi engine aircraft - and that's judged by more than one criterion. FAR25 & equivalents are all required to demonstrate the ability to reject or continue & thereafter fly to a suitable landing place. Even some Part 23 a/c have a similar requirement imposed ie Commuter Category.
Further, additional regulations in many jurisdictions force the requirement for some asymmetric ability depending on the type of operation, Australian & JAA Authorities, for example, forbid the use of single engine piston aircraft for IFR pax charter - because of the perceived safety of having a second engine in case one fails. I should add that the relatively recent approval in Australia to allow Single Engine Turbines to be used for IFR pax charter was based on them being able to demonstrate an equivalent level of safety from an engine failure perspective. There are operational limitations that light piston twins needn't observe that SET must do for an equivalent level of safety precisely because of the requirement for a certain amount of asymmetric performance.
Even the general public's belief is that the second engine provides continued flight capability. Which, by the way, is rather well reinforced with companies pervasive use of phrases such as 'twin engine safety' and the like. Admittedly the general public can't be considered to be knowledgeable in the field but the underlying expectation is still relevent. If it wasn't then we wouldn't have to spend so much time hammering into brand new light twin pilots just what that extra engine means when a donk stops (not much in the take-off or landing configuration other than profoundly degraded handling qualities in most cases).
Part 23 (non-commuter) types aren't absolved from meeting some asymmetric climb performance. But in these cases the conditions attached aren't nearly as comprehensive & the required level of climb performance ranges from poor to non-existant, perhaps only enough to fly to a better crash site. Compared to the other multi categories' required asymmetric performance they are the 'nearly there's'.
frontlefthamster, surely you're not suggesting that the a/c is not controllable at Vyse? What about at Vxse? I must disagree with your assertion that a speed margin above blue line is what provides the means to recognise & handle a failure. To say so would mean that any max performance take-off will automatically result in a Vmc departure following a failure. 'Blue line' as depicted on the ASI isn't even a fixed quantity except for a constrained set of conditions. It sounds like you're confusing Vmc (a controllability issue and itself variable from the certification figure) with Vyse (a performance issue) whilst ignoring Vxse at the same time. In that respect you're quite correct: You should not become airborne below Vmc because of the high probability of an uncontrolled crash.
Yaw, secondary roll, control inputs to stabilise the aircraft & gauge indications are the usual indications of failure - and they all occur at speeds above & below Vyse. To avoid flying at a best performance speed that is above Vmc because you believe that the speed buffer will give a better failure indication is not wise. You would look pretty foolish if an engine stops with obstacles still above you having squandered what limited energy you had prior to the failure.
Any competent & current pilot should be capaple of controlling a failure at blue line and should not need a buffer above blue line to control the aircraft. Not to be able to do so reflects poorly on the pilot's training &/or currency.
With respect to Asymmetric Commital Height, I'm familiar with the term as used in Europe. I don't think 500' is too high for it. Under adverse WAT conditions there can be a significant height loss until established in the climb. Don't know about you but even though I might be able to have the asymmetric beastie cleaned & climbing from 300' without hitting the ground , I strongly prefer not to put myself at ~100-200' (or less if things are *really unfavourable) going around on one engine with bugger all climb performance. I'd rather land beside/behind/ahead of the idiot that taxied onto the runway in front of an aircraft with a declared emergency.
And by the way, I suppose it is theoretical and my 25 years experience, over 20 of which has been flying a broad range of Part 23 twins including instructing & examining, counts for little. Even so, it's still the case that sound theory engenders good practice.
Last edited by Tinstaafl; 27th Jul 2008 at 00:27.
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Having just recently completed my first multi-engine endorsement my instructor made it clear:
Engine failure below blue line with the gear down: close throttles and land straight ahead on remaining rwy.
Above blue line: if your light you'll probably have enough performance to go around the circuit for landing. If your at MTOW theirs no chance in hell that you'll even maintain altitude, that second engine only buys a little bit more time.
Golden rule: never fly a light twin at MTOW.
I'd much prefer to have to make an extra fuel stop than to have an engine failure at MTOW and have to land a 2000kg plane in a field (if your lucky) or crash and burn in tiger country.
Engine failure below blue line with the gear down: close throttles and land straight ahead on remaining rwy.
Above blue line: if your light you'll probably have enough performance to go around the circuit for landing. If your at MTOW theirs no chance in hell that you'll even maintain altitude, that second engine only buys a little bit more time.
Golden rule: never fly a light twin at MTOW.
I'd much prefer to have to make an extra fuel stop than to have an engine failure at MTOW and have to land a 2000kg plane in a field (if your lucky) or crash and burn in tiger country.
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I'd much prefer to have to make an extra fuel stop than to have an engine failure at MTOW
We all have our favourite superstitions and I'm no different to anyone else in that regard ... however, the aim is to manage ("mitigate" as the buzz words book would have it) the risk.
There is no inherent everyday concern in launching at MTOW ... if both engines keep adding to local environmental noise pollution.
The probability of a critical failure is comfortingly low.
What is important is how you go about addressing, controlling and managing the risk of that engine (or whatever other) failure it is which is of concern.
This thread identifies a few useful techniques ... what IS important is not simply blasting off down the runway without some sort of rational plan in mind for what to do in the event of a problem's raising its ugly head.
If you can tolerate departing at less than MTOW and the cost of a tech stop .. then that is a fine technique ... the commercial reality is that it is a luxury for most of us folks.
We all have our favourite superstitions and I'm no different to anyone else in that regard ... however, the aim is to manage ("mitigate" as the buzz words book would have it) the risk.
There is no inherent everyday concern in launching at MTOW ... if both engines keep adding to local environmental noise pollution.
The probability of a critical failure is comfortingly low.
What is important is how you go about addressing, controlling and managing the risk of that engine (or whatever other) failure it is which is of concern.
This thread identifies a few useful techniques ... what IS important is not simply blasting off down the runway without some sort of rational plan in mind for what to do in the event of a problem's raising its ugly head.
If you can tolerate departing at less than MTOW and the cost of a tech stop .. then that is a fine technique ... the commercial reality is that it is a luxury for most of us folks.
Even non-commercial flights may need to take-off at MTOW. If you need to put a bum in each seat, have bags & need to fly for more than an hour or two you will most likely have to make use of MTOW. Even short trips where range ordinarily isn't a problem can need more fuel due to alternate requirements.
Asymmetric at MTOW doesn't necessarily mean downhill flight from then on. Of course with wheels, flap & unfeathered that's the most likely outcome however as long as you have the a/c under control it's worth stopping to take a moment to assess what's really happening, complete the drills and then re-assess performance. But don't complete the drills if it means losing control &/or flying into a hill. There will be circumstances where a controlled forced landing is the best option. At least you'll have the option of using some amount of power to better manage the forced landing.
Asymmetric at MTOW doesn't necessarily mean downhill flight from then on. Of course with wheels, flap & unfeathered that's the most likely outcome however as long as you have the a/c under control it's worth stopping to take a moment to assess what's really happening, complete the drills and then re-assess performance. But don't complete the drills if it means losing control &/or flying into a hill. There will be circumstances where a controlled forced landing is the best option. At least you'll have the option of using some amount of power to better manage the forced landing.
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If you can tolerate departing at less than MTOW and the cost of a tech stop .. then that is a fine technique ... the commercial reality is that it is a luxury for most of us folks.
However, I'm afraid on this occasion you have, like others here, failed to recognise that the gross risk related to the non-engine-failure-related hazards inherent in an extra landing and takeoff (the tech-stop) outweigh the reduction in risk gained by departing at less than MTOW.
Many piston twins these days are fitted with vortex generators to increase MTOW but dont have any modification to performance calculations, blue line speed or 1 inop procedure.
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you have, like others here, failed to recognise that the gross risk
that may well be so .. however, my comment was directed to the individual takeoff being considered in isolation .. at the end of the day, we have risks all around .. and, as one of our PPRuNe colleagues who specialised in risk assessment (and, unfortunately, is no longer with us) would opine .. the numbers are rubbery so the discipline has to be high.
fitted with vortex generators to increase MTOW but dont have
those I have examined in years past addressed the necessaries as part of the STC process .. I would be a little surprised to see an STC which didn't .. not to say that couldn't be the case ..
that may well be so .. however, my comment was directed to the individual takeoff being considered in isolation .. at the end of the day, we have risks all around .. and, as one of our PPRuNe colleagues who specialised in risk assessment (and, unfortunately, is no longer with us) would opine .. the numbers are rubbery so the discipline has to be high.
fitted with vortex generators to increase MTOW but dont have
those I have examined in years past addressed the necessaries as part of the STC process .. I would be a little surprised to see an STC which didn't .. not to say that couldn't be the case ..
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Golden rule: never fly a light twin at MTOW.
The Twin Comanche for example will climb at 260ft/m at MTOW (Sea Level and ISA), reducing to 100ft/m by 4000ft density altitude on one engine. But at low weight it will climb at almost 500ft/m...which could be the difference between crashing...and not.
I've come to the conclusion that if you want to always be safe and have a *guarantee* of not crashing beyond the runway due to an engine failure up to the point of Vyse when one can safely climb away you need at least 1300m of runway.
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Tinstaafl...
It's been over 30 years since I've done this kind of instruction...hate to admit, couldn't remember the details. So, I research.
In the meantime, Tinstaafl posts his reply, and I find him totally correct. Thank you, Tinstaffl, for the details.
Unfortunately, many of these light twins (less than 6000#, stall speed less than 61 KTS) DO NOT FLY ON ONE ENGINE! Now, there are exceptions to this...but this is what I taught my students...I taught them that certain twins don't fly on one engine...with certain exceptions...then, I taught the exceptions.
And, I taught that, if you're not light, not at a low density altitude airport, if you don't have lots of runway, if you don't have a nice clearway, etc., etc., you are best to use the remaining engine to take you to a 'soft spot' for a crash landing.... as Tinstaffl stated (which is Bob Hoover's philosophy, as well...'fly it all the way to the crash scene').
Unfortunately, many pilots think that, with two engines, you have redundancy. Truth is: maybe yes, maybe not....
Another misconception: Blue Line is sacred. Well, not quite.....
Blue line is correct for an aircraft at max gross weight, at a sea level density altitude. If you're less than max gross weight, your best performance is at a speed slightly less than blue line. If you're at a density altitude higher than sea level, your best performance is at a speed slightly less than blue line.
In point of fact, demonstration of this was always part of the training syllabus. I used to demonstrate this...then, have the student demonstrate this...then, we'd go back to the classroom and try to find in the manufacturer's POH where it gives specific speeds for specific weights and density altitudes. Nope, couldn't find it!!!!! What a crock of XXXX!
And, by the end of the training, the student was 'educated' as to what the plane will and will not do...and he/she was proficient in getting the most performance out of the aircraft....however much or little that was.
Fly Safe,
PantLoad
In the meantime, Tinstaafl posts his reply, and I find him totally correct. Thank you, Tinstaffl, for the details.
Unfortunately, many of these light twins (less than 6000#, stall speed less than 61 KTS) DO NOT FLY ON ONE ENGINE! Now, there are exceptions to this...but this is what I taught my students...I taught them that certain twins don't fly on one engine...with certain exceptions...then, I taught the exceptions.
And, I taught that, if you're not light, not at a low density altitude airport, if you don't have lots of runway, if you don't have a nice clearway, etc., etc., you are best to use the remaining engine to take you to a 'soft spot' for a crash landing.... as Tinstaffl stated (which is Bob Hoover's philosophy, as well...'fly it all the way to the crash scene').
Unfortunately, many pilots think that, with two engines, you have redundancy. Truth is: maybe yes, maybe not....
Another misconception: Blue Line is sacred. Well, not quite.....
Blue line is correct for an aircraft at max gross weight, at a sea level density altitude. If you're less than max gross weight, your best performance is at a speed slightly less than blue line. If you're at a density altitude higher than sea level, your best performance is at a speed slightly less than blue line.
In point of fact, demonstration of this was always part of the training syllabus. I used to demonstrate this...then, have the student demonstrate this...then, we'd go back to the classroom and try to find in the manufacturer's POH where it gives specific speeds for specific weights and density altitudes. Nope, couldn't find it!!!!! What a crock of XXXX!
And, by the end of the training, the student was 'educated' as to what the plane will and will not do...and he/she was proficient in getting the most performance out of the aircraft....however much or little that was.
Fly Safe,
PantLoad
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However, I'm afraid on this occasion you have, like others here, failed to recognise that the gross risk related to the non-engine-failure-related hazards inherent in an extra landing and takeoff (the tech-stop) outweigh the reduction in risk gained by departing at less than MTOW.
I've come to the conclusion that if you want to always be safe and have a *guarantee* of not crashing beyond the runway due to an engine failure up to the point of Vyse when one can safely climb away you need at least 1300m of runway.