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 Post subject: Re: 685 Commander
PostPosted: 25 Mar 2015, 12:16 
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No problem. It's the internet - we all misunderstand each other at times. I came up on this thread because I'm trying to decide between MU-2/690/441 for the next dream bird in 2-3 years (hey, these decisions take a while :D.)

I don't think I'd call the 690 series weak - I'd say it's a training issue, exactly like the MU-2. If you lose an engine after takeoff in an MU-2 and fly it like a 690, you'll die. If you come up on moderate to severe turbulence in a 690 and fly it like an MU-2, you'll die. I propose the commander accident rate could be reduced just like the MU-2 rate if a similar training SFAR (instead of the toothless AD 95-19-18) was issued.

Most of us hit moderate turbulence more often than we lose engines, but most of us are more scared of losing an engine than moderate turbulence. Both are fatal in the wrong aircraft if not handled correctly.

Both planes will do their jobs well if flown properly.

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 Post subject: Re: 685 Commander
PostPosted: 25 Mar 2015, 12:32 
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If you ever want a ride in an MU2, I've got a Solitaire, just let me know if you're on the east coast or Midwest. Love this thing.

I agree with your assessment of the Commander and its safety; I think the longer, less loaded wing lends itself to higher Gs in the same turbulence that doesn't really register on a stubby, highly loaded wing like a Mits. I also think the MX schedule on the Mits is very reasonable compared to that of the Commander. If you're looking at these types, don't overlook the Merlin IIIA with -10s; that's the one to have in my opinion.

The Conquest is a bad ass bird for sure, but the life limit thing turns me off.


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 Post subject: Re: 685 Commander
PostPosted: 25 Mar 2015, 12:57 
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My life limit is less than the Conquest's. ;)

From what I've read about the Merlins, they're a very borderline single-pilot plane. I don't think I fly enough to put that plane on my short list. I know very little about them.

http://www.aopa.org/News-and-Video/All- ... e-Pilot-(4)
Quote:
"But is it the airplane for you? Yes, if you'll be flying often — with a two-pilot crew — and your mission requirements frequently include multi-passenger flights over long distances. No, if you think this is just another turboprop twin. [...] The Merlin can be a bear to fly. When the heat is on, a Merlin neophyte will wish for two heads and four arms to keep things under control. The Merlin's utility comes at a price, and that price is pilot work load, systems complexity, and great attention to maintenance."

I'll take a free ride anytime it's offered, but I'm realistically a few years away from this decision.

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 Post subject: Re: 685 Commander
PostPosted: 25 Mar 2015, 14:18 
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Username Protected wrote:
I propose the commander accident rate could be reduced just like the MU-2 rate if a similar training SFAR (instead of the toothless AD 95-19-18) was issued.

Concur 100%.

One has to wonder how long the FAA can ignore the evidence for requiring type training for all turboprops.

There's been a lot of King Airs falling out of the sky lately, too, way too many IMO, and it has nothing to do with the airplane itself.

Mike C.

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 Post subject: Re: 685 Commander
PostPosted: 25 Mar 2015, 14:53 
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There is type training if you want to get insured. Maybe they very highest time pilots could slide by, but for us mere mortals, it's an approved type training and recurrent every year. Just like a type rating.

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 Post subject: Re: 685 Commander
PostPosted: 25 Mar 2015, 15:01 
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True, most pressurized twins - piston and turboprops - have "type-specific" training available and most insurance companies require it. What I found in the Twin Cessna world was that because there is no standard, there is a vast, vast difference in the quality of the courses available.

The low-end ones aren't worth the money, they use generic twin sims, and they're just ticking boxes for the insurance company. There's nothing type-specific about it.

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 Post subject: Re: 685 Commander
PostPosted: 25 Mar 2015, 19:42 
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Username Protected wrote:
There is type training if you want to get insured.

A surprising number of pilots fly without insurance, particular for the lower cost twin turboprops (like 1970s King Airs for example) where they can pay cash for it.

Mike C.

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 Post subject: Re: 685 Commander
PostPosted: 25 Mar 2015, 19:50 
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I paid cash for my Mits, I wouldn't self-insure. Blow out a window and eat a prop and the skin on one side of the stab, 100k. Gear malfunction? Hundreds of thousands.

I'm not worried about causing a problem; I can train to make that unlikely. Bad things, however, happen, and being uninsured is crazy in my opinion.


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 Post subject: Re: 685 Commander
PostPosted: 26 Mar 2015, 10:14 
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15-Oct.-2006
Narrative:
Approximately 37 minutes after departing on a 928-nautical mile cross-country flight under instrument flight rules, the twin-engine turboprop airplane experienced an in-flight break-up after encountering moderate turbulence while in cruise flight at the assigned altitude of FL230. In the moments preceding the break-up, the airplane had been flying approximately 15 to 20 knots above the placarded maximum airspeed for operations in moderate turbulence. The airplane was found to be approximately 1,038 pounds over the maximum takeoff weight listed in the airplane's type certificate data sheet (TCDS). The last radar returns indicated that the airplane performed a 180-degree left turn while descending at a rate of approximately 13,500 feet per minute. There were no reported eyewitnesses to the accident. The wreckage was located the next day in densely wooded terrain. The wreckage was scattered over an area approximately three miles long by one mile wide. An examination of the airframe revealed that the airplane's design limits had been exceeded, and that the examined fractures were due to overload failure. CAUSE: The pilot's failure to reduce airspeed while operating in an area of moderate turbulence, resulting in an in-flight break up. Contributing factors were the pilot's decision to exceed the maximum takeoff weight, and the prevailing turbulence.


I just read the full NTSB report on this accident, and several things struck me:
1) The plane was in experimental category (Market Survey) for new 5-bladed props. The props had nothing to do with the accident but one of the restrictions was was "No person may be carried in this aircraft during flight unless that person is essential to the purpose of flight." There were two pilots (in a single-pilot aircraft) and two passengers, along with all the bags needed for a trade show. The PIC had a significant disregard for the FARs.
2) The plane was more than 10% over gross. See disregarding FARs above.
3) In the minutes just before the accident, the plane was recorded on radar at a TAS of up to 307 kts. :eek: That's full cruise speed in moderate turbulence!
4) The wings broke DOWN, not UP. :bugeye: This plane was shredded by the rough air.

This leads me to the conclusion - these guys would have eventually broken any plane they were flying. The Commander had little to do with it.

PS - Va for this airplane was 148kts, not 137kts.

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 Post subject: Re: 685 Commander
PostPosted: 26 Mar 2015, 11:07 
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Jim,

"...a TAS of up to 307KTS."

Radar doesn't show TAS it shows Ground Speed

At FL230 a GS of 307KTS = about 210KTS Indicated (with ZERO Wind), factor in a 60KT tailwind (not unreasonable at FL230), and the pilot might well have reduced to an Indicated Air Speed of 148 KTS. and still have indicated 307KTS on the radar.

Something to keep in mind....

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 Post subject: Re: 685 Commander
PostPosted: 26 Mar 2015, 11:15 
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Username Protected wrote:
Radar doesn't show TAS it shows Ground Speed

Which can be converted to TAS by using winds aloft data and soundings.

Mike C.

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 Post subject: Re: 685 Commander
PostPosted: 26 Mar 2015, 11:25 
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Username Protected wrote:
2) The plane was more than 10% over gross.

Oddly enough, this can improve resistance to turbulence.

Quote:
4) The wings broke DOWN, not UP.

Typically, this indicates the tail broke first, then the nose tucked under rapidly and the wings fail in negative load.

Note that a prop change CAN create new stresses and vibrations in the tail. Ask Cessna about the 441 tail issues when it first came out which were related to prop wash vibrations.

Quote:
This leads me to the conclusion - these guys would have eventually broken any plane they were flying. The Commander had little to do with it.

If you presume equal amounts of stupidity exist over other types, then the weaker airplanes will break more often than the stronger ones since all planes are being subjected to stupid pilots.

The Commander, by the nature of that large wing, is going to be more susceptible to inflight break ups. That's just the nature of having a big wing.

The inflight breakup history of Commanders is different than other airplanes, too many have happened to simply say they attract more stupid pilots somehow.

Mike C.

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 Post subject: Re: 685 Commander
PostPosted: 26 Mar 2015, 11:27 
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Username Protected wrote:
Jim,

"...a TAS of up to 307KTS."

Radar doesn't show TAS it shows Ground Speed

At FL230 a GS of 307KTS = about 210KTS Indicated (with ZERO Wind), factor in a 60KT tailwind (not unreasonable at FL230), and the pilot might well have reduced to an Indicated Air Speed of 148 KTS. and still have indicated 307KTS on the radar.

Something to keep in mind....


In NTSB reports, that is taken into account. This report was quite specific about indicated airspeed vs true airspeed calculations but it didn't mention the exact calculations adjusting for winds aloft. It did mention KTAS and not groundspeed.

Also, (#5) they intentionally flew into areas of heavy precip. Perhaps they could have gone around it, perhaps not, but they did choose to go straight through it at cruise speed.

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 Post subject: Re: 685 Commander
PostPosted: 26 Mar 2015, 11:38 
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Oddly enough, this can improve resistance to turbulence.

NO!!! Extra weight can improve your perceived ride, but it INCREASES the stress on the airframe and wing! See the thread I linked to above for a more thorough discussion.
Quote:
Typically, this indicates the tail broke first, then the nose tucked under rapidly and the wings fail in negative load.

Note that a prop change CAN create new stresses and vibrations in the tail. Ask Cessna about the 441 tail issues when it first came out which were related to prop wash vibrations.
That's a very good point. I hadn't thought of that.

Quote:
If you presume equal amounts of stupidity exist over other types, then the weaker airplanes will break more often than the stronger ones since all planes are being subjected to stupid pilots.

The Commander, by the nature of that large wing, is going to be more susceptible to inflight break ups. That's just the nature of having a big wing.

The inflight breakup history of Commanders is different than other airplanes, too many have happened to simply say they attract more stupid pilots somehow.

Mike C.

MU-2s are more likely to crash after an engine failure, Commanders are more likely to lose wings. Pick your poison - stupid pilots can find the design limits of any airplane. Both airplanes can be made safer with proper training.

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 Post subject: Re: 685 Commander
PostPosted: 26 Mar 2015, 13:25 
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Username Protected wrote:
NO!!! Extra weight can improve your perceived ride, but it INCREASES the stress on the airframe and wing!

In smooth level flight, yes.

In a potentially damaging gust, no.

The wing can only generate so much lift. The heavier airplane is operating closer to that when the gust hits. Thus the airframe gets less added force and is heavier which translates into less acceleration, which is safer for all the parts of the airplane.

This is a decent try at explaining it:

http://www.meretrix.com/~harry/flying/notes/va.html

The confusion exists because it is counter intuitive.

When a heavier airplane flies with more weight, that doesn't allow the wing to generate more lift (force). The maximum force a wing can generate is purely a function of air flowing over the wing.

You are in more danger in turbulence in a lighter airplane than a heavier one.

Mike C.

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