Weight and Vmc?

[A Squared]

Sky west dude wrote:

>>>>Probably the most interesting thing I learned by reading a lot of twin accident reports is the lack of accidents caused by the loss of directional control on one engine (Vmc). It essentially never happens outside of the training eviornment.


Huh????? Why would you make a statement like that? Go to the NTSB website and do a search for fatal accidents for any common light twin. (PA 31, PA-23, C-310) I have, and I assure you that you will find a significant number of VMC accidents when not training. Granted, they are not as plentiful as CFIT fatalities, but they are there in numbers that far exceed "essentially never"

Regards

 

[cheater1239]

the explanation i use is in a Kershner book. my copy is out on loan so i can't provide the correct title or page info. it is either an "advanced pilot " manual or a CFI manual. 23.149 is the applicable FAR

 

[FlyinBrian]

I thought I'd make a comment about bank angle and Vmc. The previous poster was correct when he said bank is used to counteract the rudder IF DONE CORRECTLY. the greater the bank, the lower the Vmc because the horizontal lift component counteracts yaw caused by the operating engine. So your Vmc is lower at 30 degrees bank than at 5 degrees bank. However, this totally dessimates your climb performance. This is why the FAA does not allow more than 5 degrees bank when publishing Vmc. It prevents manufacturers from publishing a very low Vmc at the expense of single engine performance. Ideally, you only want enough bank to get to 0 sideslip, which minimizes drag, and makes for the best climb performance. Incidentally, the ideal bank angle is typically about 2-3 degrees in a light twin. Additionally, an ERAU study showed that in most light twins, every degree of bank beyond that decreases climb performance by as much as 30 fpm. This means that at 5 degrees of bank, you could unneccesarily be sacrificing 90 fpm. Here in AZ on a hot day, that could be the difference between life and death. Many MEI's teach their students to always go to 5 degrees bank and a half ball deflection. That 5 degrees comes from conditions under which Vmc is tested, and has nothing to do with good technique. Just some things to think about...

(Many Thanks to Mr. G Henrie for making me a better CFII and MEI.)

 

[Timebuilder]

Great post, Brian. I have found some chief flight instructors and DE's (the same person in one instance..) who adhere to the idea of 5 degrees of bank and a FULL ball width, rather than teaching the student that these ideas are transitory, and should be used as appropriate to avoid compromising single engine performance. MEI candidates should also realize that when banking into the good engine, the student will have to reduce the anti-yaw rudder they had first applied in order to hold their heading while banked.

 

[sstearns2]

Vmc accidents

The previous post was...

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Huh????? Why would you make a statement like that? Go to the NTSB website and do a search for fatal accidents for any common light twin. (PA 31, PA-23, C-310) I have, and I assure you that you will find a significant number of VMC accidents when not training. Granted, they are not as plentiful as CFIT fatalities, but they are there in numbers that far exceed "essentially never"
******

I guess it depends on one's definition of 'essentially never', but I just searched thru all 372 C-310 accidents and found 6 that were due to loss of directional control on one engine. There were about the same number of accidents caused by pilots turning the fuel pumps to high, flooding the engines and loosing all power. My point is that multi engine training, while providing significant single engine work, should reflect the fact that the general complexity of the airplane is much more likely to kill you than a mechanical failure of one of the engines.

Scott

ps- C-310s seem to have an excessive number of landing gear collapses.

 

[A Squared]

Scott,

Yes, there are other types of accidents which kill more people. Characterizing it as "essentially never" might give the impression that it isn't something that really needs to be taken seriously though. VMC rollovers can and do kill people and you need to train for them, although dying while training for engine failure is counterproductive. I looked through the PA-31 accidents and I didn't count, but it seemed like that there were comparatively more VMC rollover accidents listed for the Navajo than the C-310. In fact, a good friend of mine died in precisely that sort of accident in a Navajo. He was a non-pilot passenger. (LAX97FA217)
You make a good point that the complexity of the aircraft should be taken as seriously as engine failure. You will probably see more fuel exhastion accidents for the C-310/320 too. It has a fairly complex fuel system and if you're not paying attention you can dump a bunch of your fuel overboard. The landing gear is a problem with the 310/320. The gear legs are relatively tall and weak (especially the earlier 320s), and it's a fairly complex electromechanical system. It needs plenty of maintenence to keep it rigged correctly. I've had my share of gear problems in that airplane, none of them ending in bent metal, thankfully.

 

[sstearns2]

.......

I can't belive cessna let the fuel system for the 300 series out the door. It's an accident waiting to happen.

Your post got me to thinking that maybe we shouldn't be thinking about the number of Vmc rollover accidents there are compared to all accidents, but on how many engine failures end in a Vmc rollover situation. I'd estimate 10-20%.

Very sorry to hear about your friend.

Scott