Performance for light twins

[boofhead]

I was asking info on the Bizjets forum but it seems to have died. What would YOU have to say about whether a light twin takeoff, including Baron, Chieftan and Kingair, should be planned on the basis of an engine failure? Is it necessary? A good idea? Would you say it should be done for the turbine but the piston airplanes are exempt? If it costs money due to reducing weight or not using a small airfield, would it be acceptable to you or your company (Part 91 survey flights no passengers carried)?

[411A]

With a piston twin, you're not going to get much takeoff performance with an engine failed on the runway.
Better to close the throttles and head for something soft...if you can find it.
With a turbine powered airplane, you have a somewhat fighting chance, but it's going to be quite difficult to keep it straight, while still on the runway.
Once airbourne (at the proper speed), another story
Types such as the truboCommander and Cessna 441 do OK, larger KingAirs, likewise.

[frontlefthamster]

As a current trainer operating these aircraft, and medium jets, I can do little more than reproduce part of our SOP for piston twins (I shall paraphrase as I don't have the documents to hand, but this is accurate):

'In the event of power loss after takeoff, before the landing gear and flap are up and the aircraft has achieved and is maintaining more than blue line speed, the pilot flying shall close both throttles and configure the aircraft for an emergency landing. The commander shall transmit a mayday call or cause a mayday call to be transmitted, and shall instruct the passengers and crew to adopt the brace position. The pilot flying should endeavour to control the aircraft to minimise the severity of the emergency landing. The commander may elect to take control in the normal way. Pilots are advised, where possible, to familiarise themselves with the airfield physical environment in order to make sound judgements in this case.'

Only once through blue line (don't forget it's weight-dependent) with the aircraft clean, is it worth trying to continue. Even then, the margin of speed you have above blue line is the thing that will keep you in the air as you troubleshoot the problem and take action.

These are ex-Perf E and Y aircraft and deserve to be treated as such. Each time I pass about 500 agl with the aircraft cleaned up, I say a silent "we'll live today, then" to myself. OEI at low height after takeoff in a big piston twin will probably hurt. A lot.

None of the Perf A types I've flown are any difficulty at all with a failure at V1 of just after - but then I didn't fly the F27 in its frail dotage, and those who did, would disagree!

[411A]

Flew the F.27 (and FH227B) quite extensively, and they perform as advertised, except....at very high ambient temperatures.
Better use water/methanol...and NOT switch it off, too early, otherwise, rather large problems might be expected/observed.

[Pugilistic Animus]

Seneca and Seminole under most {reasonable} conditions climbs {sinks} like a concrete safe:}


I ALWAYS request my EFATOs in a Jet:}:}:}

[compressor stall]

It has little to do with the engine type - I suggest you read up on the performance requirements of FAR 25 vs FAR 23 certified aircraft.

[frontlefthamster]

Chicken, meet the egg...

[boofhead]

I agree with all this, but my quandary is how it applies. Part 23 is not applicable to this type of airplane (less than 10 seats). I don't know of any private (Part 91) pilot or operator who considers a loss of an engine when calculating the runway length required, for example. Yet the distance to 50 feet following an engine failure could be a mile or even more.
The chance of an engine failure is very small, yet a disturbing number of such failures results in the loss of the airplane and deaths of all on board. It is one of the true worst-case scenarios, and all the training in the world will not help if the airplane is outside its performance limitations. But most pilots use two-engine performance when planning a flight.
Should they? Is there a regulation or rule saying otherwise?

[frontlefthamster]

...and pilots flying single-engine public transport use single-engine performance when planning a flight...

Whether this is morally right or not is a matter of individual conscience, but the regulator says that it's OK subject to certain provisions (you and I might comment that they are, in fact, rather uncertain provisions).

Nonetheless, I think that twin piston public transport flown by a competent and properly trained crew is probably comparable to road travel by car. It's nowhere near train, coach, or airline levels of risk ('safety'), but it's undertaken because those forms of transport don't make sense for the clients. The same poor decision-making that will kill in a big King Air will kill in a C310... The expert pilot will have a higher probability of wringing a successful outcome out of a problem in the King Air.

[Admiral346]

I don't quite get your point...

If you are flying for your own pleasure, the smart thing would be to calculate a single engine departure, and if it doesn't work out, it's up to you to decide wether you want to do it...

If you are flying for buisness, you will have to stick to the regulations, as good or bad as they might be, I am not familiar with that type of ops... You can always say no, no matter what the big boss tells you - just for how long, though?

Whenever I have two engines, I would want to know the strategy for having one fail - or what would the point of having two be? - But then, I never fly private, I am with the airlines and might have a different way of thinking here...
Nic

[frontlefthamster]

Nic, if you ever join us in the enjoyable world of piston twin cmmercial operations, you'll get used to the fact that there are two engines for safety in case of failure, but a failure immediately after takeoff will result in a controlled crash. This is statistically acceptable to the authorities, but does require a certain preparedness from the flight crew... I hope this has helped (though I must admit I'm not sure which bit of the point you didn't get!!).

[411A]

Circa 1966.
411A is going for a checkride for his ATPL.
Two FAA inspectors are involved.
The air carrier guy watching the general aviation guy, who is watching yours truly.
Hey, this is the way it was done...then.
Anyway, after five hours, I pass.
Quite a nice job I did, too...according to the FAA air carrier guy.
He says...
'Clearly this will not climb much with one engine inop, next time please bring a DC-6, three turning is much better.
DC-6...phooey.
Next time I brought him a B707.
He was much more impressed.

[PLovett]

Next time I brought him a B707.

Show off!:}

Must endorse frontlefthamster, engine failure below blue line then close throttles and either stop or fly the thing as far into the expensive noise as possible. Above blue line there is the faint possibility of making the thing fly if things like weight, temperature, condition of aircraft and engines etc. are not too extreme.:ugh:

Just remember that multi engine piston aircraft under FAR 23 only have to demonstrate ability to climb on one engine at 1% gradient in standard conditions.:uhoh:

[boofhead]

Thanks for the input. Appreciated.
In this case I am the boss and am trying to come up with a policy, the regulations have not been a help. I want to keep the operation safe and profitable, and these two requirements do not always go together.

[SNS3Guppy]

I was asking info on the Bizjets forum but it seems to have died. What would YOU have to say about whether a light twin takeoff, including Baron, Chieftan and Kingair, should be planned on the basis of an engine failure? Is it necessary? A good idea? Would you say it should be done for the turbine but the piston airplanes are exempt? If it costs money due to reducing weight or not using a small airfield, would it be acceptable to you or your company (Part 91 survey flights no passengers carried)?


What has cost to do with it? Every takeoff, regardless of whether it's a B747 or a J-3 cub, should be planned not with the possibility of losing an engine during the takeoff, but planning for it. Not just in a light twin. Not just in a Part 25 airplane with detailed second segment performance. Even a single engine airplane should always be flown with this in mind. It's not just a good idea; there's no other way. Know what the airplane will do and where it will go, and plan accordingly.

Should you be calculating performance in a light twin? Of course.

You don't know any pilots that do, you say? I surely do. I want to know what the airplane can do on both engines, one engine, how far it will take to get off the ground, clear an obstacle, stop, what the climb rate will be, what my options are after the fact, what lies off the end of the runway, where emergency fields are, including off field forced landing sites. If you're not doing this, you're taking a very big gamble and operating on substandard level. It's just not acceptable.

Should you be limiting your choice of fields and payloads to account for aircraft performance with and without equipment failure? Of course.

Without question.

[Tinstaafl]

Part 23 twins are *not* 'true' multi-engine aircraft - in the sense that continued flight (or ability to stop/continue the take-off) should always be possible under the prevailing conditions. In that sense they are only 'partial' multis ie continued flight is only expected under a (very) limited range of flight conditions. Even that continued flight is minimal and can range from a slight climb to only a reduced sink rate.

Under 6000 lb MTOW with a Vso <61kts: Climb performance must only be 'determined' ie measure what the beastie can do. That doesn't imply that the climb performance must be positive!

Above the 6000 lb MTOW and/or Vso >61 kts: It must only be capable of a slight climb gradient (.027 Vs0 squared = ft/min if certified before 1991. Later a/c must be able to demonstrate 1.5% climb gradient).

Even that abysmally small performance requirement is under under a strictly limited set of conditions:

* 5000' AMSL in ISA
* MTOW
* Gear UP
* Flap in best L/D position (can't think of any a/c where that would not be UP)
* Failed engine prop feathered
* Cowl flaps UP
* 0 sideslip ie ~2-3 deg AoB
* MTOW

If any of those conditions aren't met then all bets are off. If you think about it, performance must be pretty bloody marginal if small drag items like cowl flaps & sideslip must be specified just to achieve the small required performance. Chances are that you *will* be going downhill otherwise.

Note: About the only day to day improvement on this is if the a/c is very light and/or the temperature is very low

So now the question becomes 'what can be done operationally to reduce the exposure to gain some semblance of Part 25 single engine safety?' along with 'is the flight today even able to make use of those techniques?' I'll presume that maintaining control of the asymmetric a/c is OK in what follows. If not forget trying to gain *any* performance. Control is the single most important thing. It's better to crash right way up & under control than to crash while cartwheeling.

You could always use very, very long runways, leave the wheels down until a couple of thousand feet while orbiting within gliding range then retract wheels & fly off. Arrival would be a glide approach from 1000' over the threshold of the same very, very long runway with the wheels down. Not very practical.

For a start you must accept that during the critical phases of flight ie take-off/initial climb and approach/landing the a/c has NO requirement for performance and nor must you expect there to be. The a/c is effectively a single engine machine with some design choices that will limit a catastrophic ie complete power loss, to only some of the available horsepower. The job becomes one of minimising the exposure period while maximising the conversion of fuel energy into kinetic & potential energy (speed & height) with the all the horsepower there is to give as much of a height buffer as possible in case one engine quits.

During take-off rotate at the POH Vr. Delay gear retraction until a landing is not possible on the remaining runway. Retract once achieving Vy. This becomes a decision point to attempt to continue flight if a donk stops. Climb at Vy to maximise the conversion of the fuel's chemical energy into height (not speed. As IAS increases so does drag which wastes some of the fuel's energy. Remember drag is a function of V squared. Even small increases in speed mean large increases in drag)

Until the gear goes up expect to use the remaining asymmetric power to achieve a better crash. If under 6000 lb/Vs < 61 kts expect that anyway but it's worth trying to fly once the wheels are up - you have nothing to lose.

All the above presume the runway isn't limiting. If it is then you can forget about covering yourself by leaving the wheels down. Rotate, get the wheels up ASAP after +ve climb, climb at Vx then Vy once clear of the obstable. The ability to operate from short runways is trade-off against increased safety margins that you can apply with longer runways.

At a safe height ie one that gives enough time to complete the engine failure drill and then fly to a runway) accelerate to cruise climb, set climb power etc

In the landing configuration s/e climb isn't part of the certification so you need to minimise exposure. Even with excellent technique there is a period where the a/c will be descending after an engine failure while you reconfigure to try to achieve s/e performance.

This sets a limit where the a/c is likely to hit something if the failure happens late in the approach and you try to fly away. At some point you will have to decide that going around isn't feasable which will commit you to landing - even if some twit taxis onto the runway in front of you. About all you can do is limit landing flap while maintaining at least Vyse or Vxse until that commital point. That keeps some hope of going around with some fast reconfiguring from approach to s/e 'performance'. With the selection of landing flap then it's not longer any use to hold Vyse since going around is now out of the question. You need to achieve Vref / Vat at some point and it's rarely blue line speed! I tend to apply landing flap at ~500', depending on type and how much of a stable approach I need and then a gradual reduction to landing speed using the extra drag.

[SNS3Guppy]

Part 23 twins are *not* 'true' multi-engine aircraft - in the sense that continued flight (or ability to stop/continue the take-off) should always be possible under the prevailing conditions.


An airplane with two engines isn't a true multi engine airplane?

The ability to maintain altitude with the loss of one engine, or to have gauranteed performance, was never the requirement nor intent of the multi engine airplane. More engines were added to increase performance, not for safety. Safety is a secondary benifit, and part of current certification standards under some regulation...but there's no doubt that an airplane with two engines is a multi engine airplane.

A single engine airplane won't maintain altitude with the loss of one either...but it's a true single engine. A multi engine that won't sustain flight is still a multi engine airplane.

That the airplane can continue a takeoff is irrelevant.

If one is flying an airplane which can't climb away on one, such as is the case with many light twins, then one needs to take that into account when planning the takeoff, every bit as much as one does so with a single engine airplane.

[frontlefthamster]

Tinstaafl,

Your remarks about speed to fly after takeoff are wide of the mark, I'm afraid. It's the speed margin above blue line which enables a pilot to identify the failure and take action. The speed loss and handling difficulties until that is done are truly frightening. Your post was very interesting, but I suspect it's the result of theoretical pondering rather than practical experience.

The height you describe in your last paragraph is known, in Europe at least, as Assymetric Committal Height (ACH). 500 ft is a bit high, 300 ft might be closer to the truth, but it's easy to establish by testing.

[ernie blackhander]

Only an engineer not a pilot so feel free to point out if i am wrong. Every flight i went on with a previous company i was with, they would actually brief themselves on taxi to the threshold, on what was plan b if everything went pear shaped. I thought it was a bit strange at the time, and thought they had little faith in me, but realised after a failure just after take off (not me)that it was probaly the way to do things, pilot still has the procedure right there in his head. I know for sure this procedure works as i have seen it in action and the outcome otherwise would have been very dismal. An overhaul on an engine is cheeper than one persons life, if it makes power give it all shes got captain.

Just got to have a dig but isn't every landing just a controlled crash?

[frontlefthamster]

Can anyone hear an annoying noise?

[Dont Hang Up]

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.

[john_tullamarine]

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 ...

[Dont Hang Up]

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..."

[jake brake]

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!!!!!

[boofhead]

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.

[frontlefthamster]

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...

[bookworm]

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.

What has bothered me since initial multi-engine training is that the commonly taught procedures assume that an engine has just two states: "good" or "duff". The procedure caters for the case where a catastrophic engine failure occurs and an immediate shutdown is necessary.

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.

[SNS3Guppy]

This is quite correct. Particularly in piston engines, partial power engine failures are far more common than complete power loss or a catastrauphic power loss.

[boofhead]

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.

[Tinstaafl]

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.

[am765]

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.

[john_tullamarine]

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.

[Tinstaafl]

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.

[frontlefthamster]

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.


John, you are very rarely wrong.

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.

[desmotronic]

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.:hmm:

[john_tullamarine]

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 ..

[Contacttower]

Golden rule: never fly a light twin at MTOW.

What aircraft was that on?

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. :eek:

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.

[PantLoad]

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

[Brian Abraham]

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.
Remember a US Navy DC-6 pilot many, many years ago getting a Bravo Zulu. Take off could be made (just - field limited) to destination and weather was such he couldn't return to the departure field if things went tits up. He elected only to load enough fuel to get him to an intermediate stop so making the take off a far less stressful event. You don't need me to tell you what happened immediately after reaching V1, having gotten some air another gave up the ghost under the strain. Some days..........

[bookworm]

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.

I've never had cause to abort a take-off/climbout at Vyse in hundreds of Twin Comanche departures, but I think you'd need a lot more than 1300 m. I'd want more like 1800 m.

[Contacttower]

You are probably right bookworm, 1300m was only a very rough calculation. The more runway the better....

What would your estimation be though of the Comanche's to climb away between 90mph (Vmc) and 105mph (Vyse)?

Piper seem to think that you'd be OK at 97mph (described as the 'take off safety speed' in the POH) but I've yet to meet someone who has had a very low level failure who can 'tell it how it is'.

[Tinstaafl]

Unless I've the wrong end of the stick, you have misapprehended Vtoss. It's the IAS to be achieved by 50' to conform to the take-off performance charts while providing an adequate margin above Vmc, not to provide asymmetric performance.

There is no requirement for the PA30/39 to be able to climb away between Vr & Vyse although once cleaned up, feathered etc it would be reasonable to expect to see some amount of climb performance if speed has accelerated towards Vxse. Can't remember if a Twin Comanche's stalls below 61kts though. If it's below then there's no requirement for positive climb performance no matter what you do. The best that its certification offers you is that its climb performance "...be determined." I'd bet a pound to a penny that unless you've reached at least Vxse with the wheels & flap up and prop feathered then downhill is the most likely outcome.

All at MTOW, of course. Given particularly favourable WAT conditions then it may well limp skywards. *Accelerating* to Vxse or Vyse would be problematic though.

[bookworm]

What would your estimation be though of the Comanche's to climb away between 90mph (Vmc) and 105mph (Vyse)?

The only person who could tell you that would be one who has suffered a catastrophic engine failure in that speed range. It's hard to suggest a realistic test at altitude, and it's nuts to suggest a realistic test at runway level. I would also agree with Tinstaafl that the 97 mph quoted is not an indication of the ability to climb.

[SNS3Guppy]

Unfortunately, many pilots think that, with two engines, you have redundancy. Truth is: maybe yes, maybe not....


A multi engine airplane which can't sustain flight, or maintain altitude with one engine failed, is still a redundant aircraft; engine failure is only one form of failure. More common is a vacum pump failure, and a light twin with two vacum pumps has far more chance of not suffering an insidious decay into partial panel than a single...or an electrical failure or a hydraulic failure.

A single, by comparison, is absolutey bound for mother earth after failure of it's one and only engine. The light twin may be headed the same direction, but with more options, a decreased descent rate, etc. Further, for IFR operations, the light twin is generally far more redundant and safer in terms of handling potential systems failures.

The second engine was never there to prevent a descent with one failed. The second engine is there for added performance when both are operating.

That the aircraft may not be able to maintain level flight with an engine failed is really irrelevant, making it no different than the single in that respect. Certainly it's redundant.

Any pilot which has received adequate instruction will certainly not believe the airplane will fly with an engine failed under all conditions. If a pilot has not received adequate preparation and doesn't take the time to calculate performance, then no amount of repeating the obvious will help him or her.

[BelArgUSA]

Thinking about the "extreme" reliability of reciprocating engines...
And the excessive power of engines fitted on light aircraft...
xxx
Looks like many people still do not "get it" in their head... yet...
With a light twin, you have twice (double) the odds of getting into deep troubles...
That is, compared to single engine airplanes. This is known, in math, as "probability"...
Exactly like "Roulette" in Macao, Monte Carlo or Mar del Plata...
If an engine fails as average every 5,000 hrs (???), a twin will have one engine failing every 2500 hrs...
Are you well trained, and fully proficient... ? Will that propeller feather as it is supposed to...?
Will your remaining engine run ok at max continuous power, for the longest minutes of your flight...?
xxx
I recall this doctor (or was he a dentist, or a lawyer)...?
Like many of these brilliant professionals, was not too knowledgeable when playing pilot.
He had an old Bonanza, which he sold to buy a PA-23 Apache...
Two motors, he told me... so much safer...! - Correct.
I was told, that if 1 engine is out, an Apache has vertical speed of about 200 FPM descent...
In English, a powered glider... Just increases your options of crash sites...
xxx
Unverified statistic I was told, by an experienced worldwide lightplane ferry pilot...
Toby was his name... "Shark-bait" was his nickname... Did numerous California to Hawaii crossings... 2300 NM...
There are more oceanic ditchings of light twins, than there are ditchings of single engine lightplanes, per flight time hours.
He told me that it was based on insurance company statistics... These are experts, are they...?
I have to say I believe him more, than doctors, dentists and lawyers knowledge of planes...
xxx
:)
Happy contrails