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.

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.

[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?