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....?
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!
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".
Last edited by AdamFrisch; 23rd Sep 2012 at 02:49.
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.
< 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.
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 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.
Last edited by Above The Clouds; 23rd Sep 2012 at 14:01.
You are confirming exactly what I have just said 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!!!
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
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.
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.
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...!
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.
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.
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
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.