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Contacttower
22nd Sep 2012, 23:23
Recently having got back into flying twins more often the question of sensible IFR take off minimums comes to mind for light twins that typically have ~200fpm climb rates engine out.

I believe for public transport the CAA specifies 600ft cloud ceiling and 1500m vis for twins with an engine out climb rate of 150ft/min and below and realistically for a non-turbo light twin that seems like a reasonable starting point considering a departure from an airfield where terrain and obstacles are not an issue. For an airfield with a lot of surrounding terrain, say in the Alps for example it might be wise to raise this to perhaps 1500ft or more to reduce the risk of hitting something if one had an engine failure in the first 1000ft of flight and to allow one to deal with the situation visually.

Flying singles I've generally tried to avoid departing IMC with 1000ft or less ceilings and essentially taken the attitude that if the worst happened in IMC all one can do is trim for best glide, keep control and head for where one believes to be the best landing spot.

With flying a twin though one has doubled one's chance of an engine failure and probably added more inertia and a higher stall speed into the mix as well...it's quite possible that in some circumstances, particularly with high terrain involved and operating from higher airfields the safety benefit of the second engine has been eroded to the point where if one departs into IMC at low level one is probably more likely to have an engine failure and then crash into something while trying to return to the field than one is likely to experience an engine failure in the first place in a single. If one does have that second engine though one might as well make a decent stab at returning to the runway. Hence why I'm thinking in more depth for light twins than I would for singles about sensible take off minimums...

What do other people think are sensible take-off minimums for twins that after an EFATO might, if light, just about manage a 2.5% climb gradient....?

Pace
22nd Sep 2012, 23:36
I have taken off in twins with a 200 meter RVR the legal minima for departures at some airfields The thing with such a departure is that you will not return so look at your weight and temperatures and make sure you will get a climb.
But yes have an idea of what you are prepared to take as a risk factor.
In a single you go down! In a twin you have more options!

Pace

AdamFrisch
23rd Sep 2012, 02:37
Depends where you are. In FAA land takeoff minimas are zero/zero for part 91 ops. Now, I wouldn't recommend it, but it's legal. In Europe, as you mentioned, the minimas seem to be higher (which is good). Do they do a distinction between commercial and private flights in this regard?

In my limited experience, the critical moment with twins are just at and after rotation and say up to maybe 300-400ft. Especially on a Vx climb. An engine failure there and you need to be on your game big time. After that it gets much easier and much safer. I'd still say it's safer than a single if one does everything right, but can go t*ts up very quickly if done incorrectly. But here's the thing with twins - you can always pull back on good engine and it will be the same as having a single. This is something they never teach in multi engine training and it's the big save-all from nastiness. Obviously, this eats altitude, but it's better to land straight and level ahead than spinning into the ground at Vmc forcing it around. Same goes for all that avoid-turns-into-the-dead-engine-stuff they teach - if you have altitude, there's nothing wrong with reducing on the good engine and turn any which way you want or fly below Vmc.

I am blessed in the 520 to have a huge draggy rudder that will keep it straight down to about 67 KIAS, which is not far above the 56 KIAS full flap stall speed. That's normally well below all my takeoff speeds (I tend to rotate at around 75-80 KIAS) except for short field Vx, so I try to keep those to a minimum. Even though they are fun to do on long tarmac just to impress the tower guys and ask for an "early turn";).

bookworm
23rd Sep 2012, 08:38
I believe for public transport the CAA specifies 600ft cloud ceiling and 1500m vis for twins with an engine out climb rate of 150ft/min and below

Not quite. Under EU-OPS, and for UK CAA public transport, the minimum RVR depends on the height from which a net flight path that clears the obstacles can be constructed.

Height RVR/visibility

< 50 ft 200 m

51-100 ft 300 m

101-150 ft 400 m

151-200 ft 500 m

201-300 ft 1000 m
> 300 ft 1500 m

Thus if you have an aircraft that, once it has its gear and flaps up at 200 ft, can continue on the required flight path on one engine (and that makes assumptions about the SID etc. -- the standard requirement is 3.3% or 205 ft per nm), then the minimum RVR would be 500 m.

Under EASA ops (for non-commercial ops as well), an LVO approval will be required for take off in an RVR less than 400 m, but there will be no other mandatory specified RVRs.

Contacttower
23rd Sep 2012, 10:33
I mean I'm more interested in just establishing what is sensible for a private flight, considering different scenarios. For example taking off from a low lying airport without obstacles and with radar available one might, as a private operator, observe a relatively low personal minimum which reflects the comparative safety of the airport. If however one is taking off from a airport 2000ft above sea level and surrounded by high terrain a much higher minimum might be in order to stack one's chances higher in the event of an engine failure. Just giving some thought to what would prudent...

Pace
23rd Sep 2012, 11:21
With a twin you get more options with more options come more choices with more choices the option to make the wrong choice!!!

To that I would add that while most light twins struggle at grosse to make a climb they fly level very happily.

If you are in an area of fairly low ground without major obstructions even at 400 feet why not go for level flight at least till you have sorted yourself out! Then ease out a climb bit by bit?

Pace

Above The Clouds
23rd Sep 2012, 11:31
Pace
With a twin you get more options with more options come more choices with
more choices the option to make the wrong choice!!!


Out of the 14 different piston twin aircraft I have flown, 95% of them will take you directly to the scene of the crash with an engine failure just after rotation, and thats without the element of surprise added in.

In the majority of cases it may well be the best option to reduce the thrust on the live engine and land ahead under control.

Pace
23rd Sep 2012, 11:46
Above the clouds

You are confirming exactly what I have just said :ugh: Yes the right option may be to close the good engine and become like a single engine failure! That becomes one of the many options you have and in certain situations maybe the correct one to take.

With a twin you get more options with more options come more choices with more choices the option to make the wrong choice!!!




Pace

Above The Clouds
23rd Sep 2012, 14:04
Pace
You are confirming exactly what I have just said :ugh:


Ok calm down, I have removed the wording "with all due respect"

strake
23rd Sep 2012, 16:13
I wonder if flying a light twin is a sensible exercise?
I did my Multi rather a long time ago on an (even then) elderly Apache out of Coventry. Firstly, I was struck by the increased cost for the little extra speed but secondly, I found that I would probably welcome the opportunity to just put a single into a field compared to workload required to keep the twin flying in some sort of asymmetric fashion.
In the end, the rating was fun but I never bothered with it after that.
Perhaps things have changed somewhat since then though :)

UL730
23rd Sep 2012, 16:37
The basic rule I use is 500m RVR and the ability to meet the published net flight path, with a 30-minute diversion that that has to be above IFR minimums.

Other factors include a requirement for centreline runway lighting and edge lighting, currency, accurate RVR readings and an appropriate aircraft loading.

In LVO - I aim critically for 200’ agl with a quick clean up of the gear on achieving positive rate on IVSI and climbing at VY (or VYSE) taking into account gyro precession.

I have only departed under LVO about half a dozen times and bar one occasion when I broke out on top at FL100+ every other time the tops were < 1000’.

Generally - I try to avoid these sorts of departures and wait for the weather to clear.

PA 23 250 Aztec

Big Pistons Forever
23rd Sep 2012, 16:42
I wonder if flying a light twin is a sensible exercise?


When flying over mountains or the ocean or at night the ability to continue flying after an engine failure means a lot to me. But the increased safety can only be realized if a concerted effort to maintain the skills necessary to deal with an engine failure are maintained.

peterh337
23rd Sep 2012, 18:32
Perhaps things have changed somewhat since then though

I think what has changed is that piston twins cost even more than they used to :)

They guzzle fuel like it was going out of fashion, they cost a lot more to maintain (not least because most of them are old, and it looks to me like a lot of their owners run them down because they have a spare engine), and keeping the pilot paperwork current costs more.

But if you want the extra motor, for flying at night / over terrain / over water / etc because it makes you feel safer, then there is no contest.

And at the top end, say a 421, you do get an awful lot of load carrying capability together with a lot of weather capability (~FL250 ceiling, pressurised, deiced, radar) which has never been delivered in a single, presumably partly because nobody produced a piston engine big enough. It is only the 700+ HP turboprops (TBM, PC12) which deliver that sort of capability (and more) in a SE, but at a far higher purchase cost.

strake
23rd Sep 2012, 19:36
Recalling that Apache which I flew in 1983, I did a quick nostalgia search on the aircraft and found the write-up below - from 1976. Although the author obviously isn't a fan, it was interesting to read his comments on SE performance - or lack of it.
PS. Rental came in at €35 an hour back then...!

Piper Apache Pilot Report (http://www.airbum.com/pireps/PirepApache.html)

Sir George Cayley
23rd Sep 2012, 19:44
An EASA proposal for a/c certification, now dropped, was for single engine complex motor fiddly controls aeroplanes should maintain a rate of climb after an engine failure :confused:

I flew a twin once where the instructor told me that at max auw if one engine failed the other would convey you to the scene of the accident. :eek:

SGC

Fuji Abound
23rd Sep 2012, 19:45
I have had one engine failure in an almost brand new twin - so those that say the risk of an engine failure in a well maintained single while statistically correct doesn't except an engine failure in any aircraft is possible. However good your forced landing skills if nothing else ending up in a field will spoil your day, will be costly in terms of recovering the aircraft and almost certainly will involve some damage - the outcome might be far worse. Be in no doubt if you fly a single that is a risk you must accept - there are no buts, no maybes, it can happen in the best maintained brand new rocket ship.

So all other factors aside with reasonable currency and training a failure in a twin en route is a non event. You pays your money and make your own decision whether that is worth a premium. Obviously twins bring a host of other advantages.

On the other side of the coin it is often recited they simply take you to the site of the crash a little bit slower (or quicker) depending on who you listen to. It is not true. It is true that some pilots flying twins should not be, and it is true that the climb performance of some twins particularly around MTOW is marginal. Ignore those rules at your peril. However, respect recurrent training ensures competency and in reality few flights will be at or close to MTOW.

Flying a twin is rewarding. There is no doubt they are a much more stable platform. Chances are with both engines they will be a great deal more capable than a single, and make the right choice, and they don't perform too badly with a failed engine.

So if you are in the market for a twin and understand the costs involved dont listen to the nay sayers, there is a lot to be said for two engines and the risks are overdone by those than haven't flown twins and don't understand whats needed to make their operation safer than flying a single.

AdamFrisch
23rd Sep 2012, 20:17
Agreed Fuji. After the initial scare when my left engine lost two cylinders, I was surprised at how calm I was and what a non event it turned out to be.

Old Akro
24th Sep 2012, 08:20
I think this is an easy answer. Regardless of minima, flying IFR privately, I only take off from airports I can land at again. There are many reasons short of engine failure you you might want to land again: popped door, popped baggage door, instrument issues, sick passenger, forgotten charts, loose fuel cap, undercart issues, etc. When you've got discretion on when you go, why make it harder than it needs to be? Typically it only requires waiting a couple of hours for a lift in the weather.

The thing that is frequently forgotten about twins, is that there are many other failures where the redundancy of a second engine is valuable. Vac pump failure, alternator failure are top of the list. I've never had an engine failure, but I've had 3 vac pump failures and an alternator failure in flight. These are a complete non event in a twin, but a serious problem in a single.

The emotion and cries that the second engine only gets you to the scene of the accident focus on total engine failure in the first 3 minutes or so of flight. Engine failure in cruise (statistically much more likely) is a non event in a twin (below critical altitude). Also a twin gives you plenty of options that a single doesn't in the event of a partial engine failure or rough running engine or engine failure on descent.

Twins are poisonously expensive, but no one I know who owns a twin would ever go back to a single for IFR, night or long cross county flights.

Pace
24th Sep 2012, 11:40
Like Fuji I also had an engine failure in an almost new twin!
The accident rate on light twins is bad but IMO part is due to lack of currency most is due to the training which is not specific to LIGHT twins and I stress that word.
Pilots are trained to go for blue line and have it so inground they fail to think out of the box and consider other options.
It maybe to close both throttles and take to a suitable field!
It maybe to ignore a climb and to purely establish level flight were light twins are happy doing!
I can remember flying demo work for the main Piper dealership as was at Bournemouth!
For fun we completely shut an engine down and flew it single engine right across the channel!
Crazy thing to do maybe but the twin was as happy as Larry so why attempt blue line if the situation does not make that a good choice?
In my engine failure 3 rocker shafts completely sheared due to over torque at manufacture.
The aircraft was vibrating badly. The unit went at 200 feet and at grosse weight!
Had I gone conventional I knew by the feel of the aircraft that I would go down!
I had maybe 30% power on the sick unit and kept it going with one hand poised on the prop lever until I got to 800 feet where I shut it down in level flight!
IMO more should be taught at looking at the options! Going for blue line maybe the best but could also be the worst

Pace

peterh337
24th Sep 2012, 12:57
The accident rate on light twins is bad but IMO part is due to lack of currency most is due to the training which is not specific to LIGHT twins and I stress that word.

I am sure that's true, but isn't that all a part of the package when it comes to deciding what to fly?

If I won the jackpot tomorrow, I don't think I would go and buy myself a Citation. Why not; I could easily afford one, or a few. I wouldn't buy one because on my flying (100-150hrs/year in a TB20, 140-150kt, translating to 1/2 that in something 2x faster) I would never be current enough.

Pace
24th Sep 2012, 13:18
Peter

This might surprise you but I find the Citation is easier to fly than a Seneca twin and a Kingair : )
Speed is relative but the Citation makes things easier for you in a lot of circumstances ; )
You would find one a doddle to fly! I can get a Citation from cold ready for takeoff within five minutes you won't do that with the TB or the Kingair or a Seneca ; )

Pace

peterh337
24th Sep 2012, 14:42
Money aside, I would still choose a TBM over any piston twin.

I've done a fair bit of IFR flying around Europe and my view now is that just having a "tank" capable of boring a hole through any weather, simply because it has boots and heated props and a heated front window panel, and hopefully radar as well, is not the way forward.

The way forward is to fly high up, above most "organised" IMC.

Pistons can do that - any half decent turbo job can do FL240 - but you are rapidly into fairly inconvenient (for passengers, anyway) oxygen arrangements, so this leads to pressurisation, and there are very few options for that. The PA46 is the only one currently in production, the other pressurised singles are all variously old wrecks, and pressurised piston twins are also all finished (Baron maybe?).

That's why a piston twin would not feature on my list. Not because I would have to re-do all my paperwork, which I would, but because - short of a 421 type plane which guzzles avgas by the barrel - it would not deliver pleasant flights.

This summer has exposed (http://www.peter2000.co.uk/aviation/edny3/) this stuff more than any I remember. FL200 in a TB20 is right at the very top of what is possible. Yet this is as much as any non-turbo twin will do.

The real way forward in mission capability is not a 2nd motor, but pressurisation and a FL250+ ceiling, and radar.

That's why the only meaningful upgrade from say a TB20 is a Jetprop ($1.2M for a reasonable one), not a Seneca or similar, and not even a turbo Seneca.

Statistically, a single PT6 engined plane is much less likely to go down than a piston twin. Emotionally, this is hard to swallow, and impossible to swallow for the regulators (who demand 2 motors for PT, yet ban a single PT6 for the same job), but the numbers are very hard to argue with.

AdamFrisch
24th Sep 2012, 15:08
Peter

I'm sure adding a multi to your licenses would be a very simple and cheap thing.

If you did, you could be travelling in what you say is the kind of plane you require for your missions. For $300K you could be in a MU-2 tomorrow that burns only marginally more than a turbine single. Fuel consumption follows SFC and horsepower, therefore a twin never burns much more than a single with equivalent horsepower. Also, the Garretts are more fuel efficient than the PT6s. The MU-2 does 300kts, FL300 with all the mod cons. That would be twice as safe as a TBM850 and would leave you $1million to spend on fuel.

Or a Conquest or Turbine Commander. But the MU-2 is the most bang for the buck. Well supported as well. And if you've ever been close to one, you know how well built they are. No oil canning panels there...

peterh337
24th Sep 2012, 15:16
therefore a twin never burns much more than a single with equivalent horsepower

Depends on how you define "much" :)

Re the MU-2, I would definitely want to be current...

UL730
24th Sep 2012, 15:19
Unfortunately - you sometimes have to climb up through "organised IMC" and descend. :sad:

I believe the low pressure system currently over the UK is 7 miles thick.

I think what has changed is that piston twins cost even more than they used to

They guzzle fuel like it was going out of fashion, they cost a lot more to maintain

Ain't that the truth.

peterh337
24th Sep 2012, 15:36
you sometimes have to climb up through "organised IMC" and descend

Very much so, of course...

There is where you need the equipment.

But one needs a better solution for the enroute part. Radar (or a stormscope) won't protect you from some pretty nasty turbulence.

UL730
24th Sep 2012, 16:16
At FL250 you can be just in the really turbulent outer edges (isotachs) of the jet stream. Difficult to see and a interesting ride if you encounter this phenomena.

I have driven TBM700 after viewing one at Farnborough and the guys from Tarbes would not let me go unless I had had a test flight. Competent aircraft although the model behind your excellent report and given a million dollars an excellent choice.

My instructor at Humberside drove King Airs and MU2's professionally before and after his training business and he was a very wise old bird with 25000+ corporate hours. The MU2 was his weapon of choice but with that wing - you had to be super current. Just to emphasise the attention to detail - he ferried one from USA and the wrong grease was used in the gear that froze up en route. Slightly nervous approach into Reykavik with 0 greens. There are so many aspects one has to consider with HP a/c at high altitude.

Sorry for the drift Above the Clouds.

peterh337
24th Sep 2012, 17:02
the wrong grease was used in the gear that froze up en route.

I've had that (http://www.peter2000.co.uk/aviation/pontoise/index.html) on the TB20. Pitch trim froze solid at FL140. 1st flight after the Annual. The MO denied putting anything in there.

That issue is actually quite common. I know of a Citation which froze in the climb and was thus flown all the way to Spain with a suitcase jammed between a man in the RHS and the yoke, for a few hours :) He was lucky he had someone else around to insert and remove the suitcase.

Pace
24th Sep 2012, 17:48
Peter

On a black winter night taking off and flying over extensive fog banks in the black below I dont care what the stats say or dont say I like a second power unit :E
Regarding flying over weather you really need to get up to FL370 FL380 to get on top.
I have met extensive Walls of CBS down near Biarritz and around the Alps as well as over Croatia where a Turbo Prop would not have hacked it!
TBM is a great machine but very interesting is Eclipse which is turning out into a good machine under Sikorski ownership should get in and out of 800 meter strips climb to FL410 and sips fuel!
Range and payload not bad either.

Pace

Above The Clouds
24th Sep 2012, 19:48
UL730
Sorry for the drift Above the Clouds.

No problem, the old piston twin is an interesting debate, something that gets lots of people hot under the collar, I don't think about it much these days as I operate with 3 very reliable jets engines :) but have done my fair share of piston twin operations worldwide over the years.

AndiKunzi
6th Oct 2012, 21:03
my take-off minima for private operations with my Seneca II:
200 ft ceiling and 400 m visibility on a runway at least 4000 ft / 1,200 m long, 100 ft wide, ILS, flat terrain around, near MSL, 20 ° C, at 2,000 kg / 4,400 lbs. Things change a lot with terrain, density altitude and mass.

Clean-up (gear, flaps, vyse) as soon as possible;
if an engine fails when cleaned up and the runway is very long - lets say 8,000 ft, even being at 300 ft in the clouds I'd always close the throttles, gear down again, flaps when runway in sight, and land. At low visibility ILS is always set to HSI 1 initially.

I've simulated single engine go-arounds and stuff like that at a safe altitude (4,000 ft above the ground, one engine shut down completely). If the aircraft is well maintained, the second engine will bring you to the next airport safely. I recorded climb rates at 250 kg below MTOM, 6,000 ft DA, that were identical to a Cessna 150 at MTOM at the same altitude. So it's not a glider. At this altitude, 65 % on one engine gave me 94 KIAS (vyse + 5 kts) at 10.5 GPH. A lot of endurance available (I had 110 GAL in the tanks) to think over all options and not even challenging to fly for a properly trained pilot.

When being in hard IFR, over water, at night or during the winter time, I just want to have that second power plant, like said before. Even on a PT6, the prop or its governor could fail. What is true: too many twin accidents occur because of wrong emergency procedures, leck of trouble-shooting and the wrong choice after an engine failure close to ground. Better close the throttles and overshoot the runway in the unlikely event of an engine failure short after lift-off.

Emergency landing in a turbine powered causes much higher speeds and thus risks compared to C172, although the event is rather unlikely. But one day production failures might affect even a PT6, and if it is only due to a supplied part, the fuel system or the prop.

With both engines running, a twin offers a much steeper angle of climb than most singles, which adds safety.

A sudden total engine failure is not the normal case. In many cases, power on the affected engine can be reduced before things get worse (e.g. loss of oil) or partial power is still available (loss of one magneto). I've experienced both of this. The oil leak in C303; at least I could see the oil running out of the engine, because the engine wasn't in front of me; reduced power to idle, landed uneventful 30 min later, still 3 qts in the engine which survived (the leak was easy to fix).

To reduce the risk of an engine failure due to high engine load and especially right after departure, I maintain below max. MP during take-off on long runways (e.g. 38" instead of 40") and reduce to 75 % at 300 ft AGL.

I regularly do fly without the aid of the autopilot in solid IMC, practice crosswind landings, approaches in low IMC and emergency procedures. The redundancy of all the instruments and power sources (gyro air, electrics) is another important benefit. However, the pilot must be able to cross-check all these redundant instruments during an approach to minimums. Adequate cross-checking (altimeters, both LOC + GS) is trained rarely, unfortunately. Many instructors and examiners even don't want to put both HSIs / NAVs on the ILS, but the second one already for the missed approach.

These are just my thoughts about flying safely in marginal weather.

Best regards,

Andi

englishal
7th Oct 2012, 09:42
I think there is a lot of nonsense talked about light twins personally ;) The accident rates are far BETTER than a light single - go check the NTSB website and see for your self. If you look at twin accidents, the accident rate is far less but the fatality rate is higher. Most of the accidents seem to be CFIT type accidents and not aeroplane failure accidents or "loss of control". They are more of a handful but then again someone who regularly flies a twin will be a more experienced pilot (in general), probably explaining the low "loss of control" type of accidents.

Secondly, in all the light twins I have flown, I have always been able to climb single engine. True I have probably been below MAUW, but that is how I mostly fly a Twin anyway - 3 or 4 of us for a weekend. Even a dodgey old Seneca II has a single engine service ceiling of 13000' and it will readily climb up there. I failed an engine on a DA42 at 6000' over California with 3 POB and plenty of fuel and we were climbing quite happily with no drama. As many instructors say, it is quite boring, and boring when flying is a good thing unless you are doing aeros :)

But back to the OP's question - what do you feel safe in? I took off out of Edinburgh in a Single in 600m RVR and 200' OC and rain. I had the GPS on showing me the Forth in case we had to ditch but I didn't feel particularly worried. At 4000' we were on top in glorious sunshine (apart from the Cbs towering around us but that is another story!).

My buddy who flies bizjets is very loathed to even cross the channel in a SEP these days - maybe with age and experience your fear increases, which is why in the USA when flying around California / Nevada and the hostile terrain there I now nearly always rent a twin !