High accident rates in light twins an alternative?
 

We all know that the accident rate for light twins is attrocious with an engine failure.

Infact I believe you are more likely to survive a single engine failure and the subsequent forced landing than an engine failure in a twin.

Most light twins at best at grosse weight on a standard day are hard pushed to climb at 200 fpm and those figures are achieved on new aircraft with new engines, not old hanger rash aircraft, covered in flies with tired old engines.

With the second engine comes more options and with more options comes more opportunities for making a mistake.

I appreciate the high accident rate is partially due to the fact that most private pilots cannot afford to fly light twins and as such are not current enough to cope.

But where does the training figure in this high level of accidents.
We are taught to act in a particular way to an engine failure and have it drummed into us to such an extent that we go into mental autopilot and with the aircraft cleaned up go for blue line and a climb.

I have had three engine failures in my time. Two partial one full. One was at grosse and at 200 feet in the climbout. The aircraft was shaking badly but the engine was still producing some power. I elected to keep it going as even with some power I realised that I was not going to climb at all if I shut it down. I had one hand on the prop lever ready to pull it if there was a bang and then once up at a 1000 feet shut the engine down. The cause was three Sheared rocker shafts.

Another alternative was put to me by an ex fighter pilot for light twins and may be an option to add in certain circumstances.

While light twins are happy to fly along in level cruise with one shut down all day they are pathetic at best at blue line climbing. You only need a gusty day with downdrafts a desperation and fix on climbing and it is only too easy to get below blue line, get further crossed up, add further drag and loose the plot.

Once in the air an aircraft does not know that it is at 300 feet or 1000 feet and mayb in certain situations it might be better to go for level flight at 300 feet rather than the drummed in climb. Most airfields are not enclosed by high terrain and usually have a gentle turn route through where you can maintain level flight at your 300 or 500 feet. Once trimmed for level flight and at single engine cruise speeds step climb the twin in gentle increments using the trim. As the cruise speed bleeds off level again and repeat until you have sufficient hight to return or land at another airfield.

ThIs does work and while not suitable for all situations it is another option to consider if you get into a mess.
It is certainly worth trying in training with a safety pilot/ instructor and at altitude.

Pace

Blue line is the best climb speed on one engine. How is climbing, however slowley, better than maintaining altitude?

>Blue line is the best climb speed on one engine. How is climbing, however slowley, better than maintaining altitude?<

Because you may not be climbing at all at blue line and without speed your margins are smaller and it is easier to get below blue line with all the horrors of increased drag and a dramatically worsening situation which shows up in the appalling twin accident rates with one engine out.

But I am NOT putting this forward as a replacement to blue line climb but an extra alternative in certain situations. Go try it in a safe situation and make your own mind up.

Pace

I do see your point Pace, but the physics don't add up. It sounds a bit like the old "Getting it over the step" myth.

If you aren't climbing at blue line speed, i.e you are only just maintaining altitude, then you are using all the available power. If you don't have excess power to climb, you also don't have excess power to accelerate. If you DO have excess power to accelerate, you are always going to ALSO have excess power to climb.

What you seem to be getting at is keeping some extra margin over blue-line to alow for gusts etc. Fine- but holding a constant speed just above blue-line is going to be more efficient and give you a better net flight path than the "saw tooth" flight path you seem to advocate.

Unfortunatley there are no free lunches in physics- either the power is there or it isn't!

Interesting question - are there any hard statistics for this?

One way of solving the asymmetric problem is to close all the throttles! Ok you become a glider then but at least you are under control!

One thing the BA777 at LHR proved is that if you are going to crash then keep the wings level and don 't stall!

Your question only considers the take off situation. There are other occasions where it's nice to have two engines - flight over water or inhospitable terrain and/or night or IMC!

Reminds me of the definition of the ideal a/c when the engineer taps the captain on the shoulder to tell him "We've lost number 4" - the Captain replies "Which side?"

Ok yes light twins can be challenging but on balance I would rather have another engine. There are also aspects such as having 2 alternators and 2 vacuum pumps which mean more redundancy.

It would be interesting to know how many accidents have been prevented because the type was a light twin and not a single.

>If you aren't climbing at blue line speed, i.e you are only just maintaining altitude, then you are using all the available power. If you don't have excess power to climb, you also don't have excess power to accelerate. If you DO have excess power to accelerate, you are always going to ALSO have excess power to climb.

What you seem to be getting at is keeping some extra margin over blue-line to alow for gusts etc. Fine- but holding a constant speed just above blue-line is going to be more efficient and give you a better net flight path than the "saw tooth" flight path you seem to advocate.

Unfortunatley there are no free lunches in physics- either the power is there or it isn't!<

Wizofox

But it is Physics and there are no free lunches as you put it but the wrong way. With one engine out in a climb you have drag that you do not need to have. You have extra drag from a higher angle of attack on the wings and the slower you are the more rudder you will require to combat the yaw.
Its all a vicious circle.
By reducing the pitch you are reducing the drag and hence the aircraft will make the most of the available power and accelerate as it accelerates less rudder sticks out in the airstream.

On a hot day at Grosse weight your other engine might be there to carry you to the crash site. Before you make a forced landing this trick might work. As I Said go try it as its another option up your sleeve before taking to the trees.
And yes it is all about Physics so please do feel free to pull the Physics apart because it is for discussion.

Also remember we are always playing with available power and drag but we always have another source of extra power, an extra engine if you like and that is the kinetic energy inherant in the aircraft by using pitch or your
control column.

In a single engine aircraft with the engine out you have only that spare engine (kinetic energy) to maintain your speed to a forced landing. Instead of your throttle controlling your power. Your control column becomes your throttle and you are trading altitude to get that energy

Pace

flybob
 

B52 by any chance?

>Your question only considers the take off situation. There are other occasions where it's nice to have two engines - flight over water or inhospitable terrain and/or night or IMC!<

Fireblob

This is my point. You loose an engine in the cruise and its no major deal to shut it down and fly for miles on the remaining engine the plane does not know whether its at 4000 feet or 400 feet and behaves roughly the same.
But the same plane asked to climb? and you are in a totally different ball game.

Pace

RadicalRabit

No this is a serious point for discussion. I have over 2500 hrs in light twins alone and your welcome to my ATP numbers to a private E mail.

Pace

Whilst agreeing that the single engine performance of most light twins is very poor, I'd be interested to see your accident statistics backing up the initial premise - I'm usually quite on top of the accident reports and don't recall seeing many, if any, reports of losses of light twins following single engine failures.

G

All this talk about light twin accidents being 'attrocious' quite frankly is without hard facts.
In the USA, the accident rates for single and multi-engine airplanes are about the same.
However, what you don't hear about (nor reflected in statistics) are most of the multi-engine airplanes that have an engine failure enroute, and land just fine, thank you very much, at an airport.

Singles?
Usually make the news, simply because when the engine quits, you either find an airport (usually doesn't happen) or end up in the weeds somewhere.

The NTSB accident reports are there for all to read...and learn.

Of course, in other countries...could be totally different.

Mr. Boffin
 

No losses of aircraft (light twin) after OEI? Pretty bold statement, Sir. I know of two in my circle of aero alone. I'll check some more for you.(411: "atrocious" is in the eye of the beholder, your call isn't the Cessna 411? One would hope)

Airfoil

Pace,

Drag is made up of form drag, which increases as the square of velocity, and induced drag, which does indeed increase with angle of attack.

This is where we come up with the drag curve, where drag is minimum at a particular speed/angle of attack, and increases with EITHER an increase OR decrase in speed or angle of attack.

Vyse ("blue line" speed) is speed for maximum excess thrust on one engine, but is very close to the minimum drag speed. You are correct that drag from control inputs are a factor, but are included in the flight test data to determine Vyse.

Yes, but if you reduce "pitch" (I think you mean angle of attack- there is a difference) before you accelerate, you also reduce lift. If you were only maintaining height at Vyse, you are now descending. Sure you'll accelerate, but, as I said above, as you were at your minimum drag speed before, flying faster is only going to increase total drag and make things worse.

The blue radial is there for a reason. It really is the speed for best climb performance on one engine.I have a similar amount of light twin time as you (though a lot of years ago!) and I know that sometimes equates to "Not very much!!", but it is the best you are going to get. Fly any other speed, faster or slower, and you degrade the aircrafts climb performance.

I think I understand what he's saying. He's not saying that nosing over will find you some extra power you weren't making before, but rather assuming you've got a small but positive rate of climb, so you do have excess power available by definition. Therefore it is conceivable that you might be able to reduce your workload by trading a climb that really isn't getting you up very fast for a little extra airspeed so long as you're above the surrounding terrain. Obviously, if you weren't climbing a Vyse, this would go right out the window.

However, I think the improvement in handling qualities would vary from aircraft to aircraft depending upon how wide the spread between Vmca and Vyse is and the few extra knots you gain might not be worth it.

I remember reading a very intersting article in one of the big General aviation "Comic books" when I was going my initial ME rating, written by one of the well knwon gus, whos name escapes me now.

Up to that point I had read all the material the good people at Jepps and the FAA had written on dealing with Engine failures shortly after takeoff, as well as my instructor. Essentially, get it cleaned up, and climb away at Blue Line.

The author of this article stated that Comair, who started out in life operating only light twins such as the Navajo had suffered serious accidents as a consequence of Pilots loosing an engine, and tring to climb away at blue line, but due to the face that they were nearly always at MAUW and in hot conditions or high locations, had resulted in speed decaying and loss of control in flight at low levels.

Their revised policy was this:

Engine Failure from 0ft-500ft, close throttles, land straight ahead.

500-1000ft Close throttles land ahead, with turns of up to 40 deg left or right

Above 1000ft Attempt to climb away at blue line.

The reasoning was that it was far more likely to go below VMC and violently loose control at low level resulting in a large smoking hole, then to have a more then likely survivable forced landing under control.

I only did about 15 hrs Multi Engine Piston and I fly Jets now, but I often wonder still, if I had found myself in that position would I have gone with conventional wisdom or the other option. Pardon my ignorance.

>Yes, but if you reduce "pitch" (I think you mean angle of attack- there is a difference) before you accelerate, you also reduce lift. If you were only maintaining height at Vyse, you are now descending. Sure you'll accelerate, but, as I said above, as you were at your minimum drag speed before, flying faster is only going to increase total drag and make things worse.

The blue radial is there for a reason. It really is the speed for best climb performance on one engine.I have a similar amount of light twin time as you (though a lot of years ago!) and I know that sometimes equates to "Not very much!!", but it is the best you are going to get. Fly any other speed, faster or slower, and you degrade the aircrafts climb performance<

Wizofox

Yes I do mean angle of attack :-) I can give you some figures off a Seneca Five. With an engine shut down and feathered it will cruise at 127 kts compared to 155 kts with both going and that is with a high cruise setting not max power which you would have trying to climb at blue line which is about 90 kts.

So we have a difference at a lower power setting of nearly 30 kts.
That difference is purely down to drag nothing more nothing less.

Faster air over the wings creates more lift meaning that you can reduce the angle of attack and hence the drag for a given amount of lift.

In the situation we are talking about where because of tired engines a bug splattered airframe, temps, weight etc where we have max power, blue line and no or negligable climb then yes as we reduce the angle of attack initially the aircraft will start a very slight descent. As the speed increases so does the lift meaning you can reduce the angle of attack even further and even further again as the speed continues to increase to a cruise single engine speed.

As I said do try it :-)

Pace

>The author of this article stated that Comair, who started out in life operating only light twins such as the Navajo had suffered serious accidents as a consequence of Pilots loosing an engine, and tring to climb away at blue line, but due to the face that they were nearly always at MAUW and in hot conditions or high locations, had resulted in speed decaying and loss of control in flight at low levels.<

Telstar

I agree Landing ahead is a last option and I am putting this forward as a further option which can keep you in the air rather than down in the trees. I have tried it and it does work.

If there were good twin accident statistics engine out I would shut up but they are attrocious and to me the training and options trained are not complete for light twins ONLY.

If anyone wants to argue the Pyschics feel free as I am purely opening up a discussion not trying to win points

I am not trying to reinvent the wheel but wonder whether the wheel was totally round in the first place regarding light twin training. The problem could be that historically light twins have been used to train for bigger stuff that climbs at 1000 fpm engine out and the training doesnt look at the light twin on its own.

Pace

AirfoilMod - I don't dispute that accidents must occur since I don't manage to read every accident report in the world and I'd be amazed if there aren't some SEI related accidents. But are they really significant in the global scheme of things - that is compared to other accident causes, or for that matter in terms of engine failures causing accidents when they do occur? I'm happy to be convinced, but I've not seen the stats to do so.

G

By any chance do you mean that L= CL*1/2 rho*V>2? Cause it does.

If what you said above were true, then the faster you went, the less total drag you'd produce, and the aircraft would just keep accelerating until it approached the speed of light! Congratulations, you've just invented perpetual motion and solved the universes energy crisis!!

Induced drag is one side of the story. On a typical light aircraft it reduces to near its minimum value at about 5deg A of A, and peaks at CLmax, which is to say stalling angle.

But as speed increases, so does form drag.

Tell me, if you put your hand out the window of your Seneca at 127kts as opposed to 90 kts, at which speed would you feel the most drag? That's called form drag which, as I explained, increases with velocity. Do you dispute this?

So, you have one form of drag that INCREASES with speed, and one that REDUCES (though, after a while, only by a little). At some point, the sum of these two values is at a minimum, and that is Dmin, which is very close to Vyse.

Hav a look here:- http://selair.selkirk.bc.ca/aerodyna...rag/Page9.html

Your Seneca may be able to maintain a Tas of 127 at altitude, but it won't sustain a climb at that speed. The maximum sustained rate of climb occurs at a particular speed, and the nice guys at Piper even put a blue radial on your ASI to let you know what it is.

By any chance do you mean that L= CL*1/2 rho*V>2? Cause it does.

>If what you said above were true, then the faster you went, the less total drag you'd produce, and the aircraft would just keep accelerating until it approached the speed of light! Congratulations, you've just invented perpetual motion and solved the universes energy crisis!!

Induced drag is one side of the story. On a typical light aircraft it reduces to near its minimum value at about 5deg A of A, and peaks at CLmax, which is to say stalling angle.<

NO because at the end of the day the airframe is pushing through air and there will always be a terminal velocity for given power. Hence even a sky diver will hit a terminal velocity. As you know the higher in the atmosphere the faster you go.

>If the BEST rate of climb is zero, flying any other speed produces a descent.<

Yes if you have 90 kts and blue line and you are only staying level any reduction in the angle of attack will result in an initial decent and an increase in airspeed as Kinetic energy comes into play and assists the energy produced from the engine. But then as airspeed increases the lift increases for a reduced angle of attack and the descent rate will reduce until as the airspeed increases further you will finally achieve level flight at single engine cruise speed.


The same as pushing a wooden spoon through custard and water and a wooden spoon isnt a wing and neither is the sky diver.

I am fully aware of other forms of drag and your theories on how blue line is calculated for single engine climb. But as you know only too well at best lighttwins do not climb very well and at worst dont at all, You are also very close in speed to where if you get below blue line the drag increases dramatically and that is the killer.



Pace