Looking for a DER

Ted

Ted

The pilot formerly known as Twin Engine Ted
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iFlyNothing
I’m interested in finding an independent DER who can approve data for airframe limitations changes.

Maybe such a thing doesn’t exist. But I know it does for other aircraft systems.
 
Doc Holliday said:
What are you looking to change?
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N228WP (an MU-2B-20, F model) has a ceiling of FL250.

The Solitaire (MU-2B-40, still a short body and physically effectively identical, at least for the fuselage/wings/tail) has a ceiling of something around FL330.

I don’t see RVSMing the plane so FL330 doesn’t necessarily do much for me, but I’d like to be able to apply the ceiling of the later planes so I could legally fly higher (say up to FL280). The plane can do it performance wise for many weight/temp combinations (no I haven’t tried - but I can interpolate based on observed performance at 250). The extra efficiency, tailwind potential, and ability to get a little higher over some weather would be very helpful for the kind of flying I do.
 
What's the pressurization differential? What cabin do you have at 250?

Does the MU-2B-40 have a different cabin differential?
 
You are correct, the Solitaire has a higher differential. I suppose I wonder why that by itself matters. When I flew a Commander 690 (or even the Cheyenne II), the ceilings were in the 30s with a similar 5-5.2 psi differential, so you’d be above 10k cabin near the ceiling. Obviously can’t do that 135 but I’m flying 91.

At FL250 my cabin altitude is about 8,700 according to the plane’s gauge and the Guardian monitor I have.
 
So what would your cabin be at 280?

I can't put my finger on it right now, but the 250 limitation on some aircraft have a reason (certification).

BTW, 8700 at 250 is pretty good. Sounds like you have a fairly tight cabin with minimal leaks.
 
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Ted DuPuis said:
Maybe such a thing doesn’t exist.
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They exist. But there are 2 separate TCs involved between the -20 and -40, both still owned by Mit Heavy Ind. That in itself would be a hard nut to crack to use data between TCs. I'd recommend a prelim call to a ACO before a DER.
TCDS -20
https://rgl.faa.gov/Regulatory_and_...2F209D674754572086257F70005D6A14?OpenDocument
TCDS -40
https://rgl.faa.gov/Regulatory_and_...B2EF55D312BB0FCD8625768700528381?OpenDocument

Current DER listing:
https://www.faa.gov/other_visit/avi...gations/designee_types/media/DERDirectory.pdf
 
Doc Holliday said:
I can't put my finger on it right now, but the 250 limitation on some aircraft have a reason (certification).
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Does it have something to do with lack of testing in emergency descent?
 
Ted DuPuis said:
I’m interested in finding an independent DER who can approve data for airframe limitations changes.

Maybe such a thing doesn’t exist. But I know it does for other aircraft systems.
Click to expand...
I believe that you have one step beyond getting the DER (hard for me not to type RCE, ya know!) to sign off. Not many field approvals are being granted lately, it seems. If you are going to develop a saleable STC for the increased altitude, it may be worth it (and it may be worth finding out if the airframes are truly identical, so that perhaps the outflow valve, etc. could be upgraded to get higher differential).
 
What sort of emergency oxygen do you have for the cockpit and the cabin in the MU-2?
 
Doc Holliday said:
Perhaps. That 250 number sticks in my mind for some reason.
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The reason that came to mind is that I remember the MEL for the Lear 35 restricted flight to 250 when the spoilers were deferred. I was told that this was because it was certified for the emergency descent procedure with spoilers.
 
Doc Holliday said:
So what would your cabin be at 280?

I can't put my finger on it right now, but the 250 limitation on some aircraft have a reason (certification).

BTW, 8700 at 250 is pretty good. Sounds like you have a fairly tight cabin with minimal leaks.
Click to expand...

I’d expect the cabin to be right about at 10k at FL280. And yes, the cabin is very tight. It needed a door seal when we first acquired it but it does very well.

Bell206 said:
They exist. But there are 2 separate TCs involved between the -20 and -40, both still owned by Mit Heavy Ind. That in itself would be a hard nut to crack to use data between TCs. I'd recommend a prelim call to a ACO before a DER.
TCDS -20
https://rgl.faa.gov/Regulatory_and_...2F209D674754572086257F70005D6A14?OpenDocument
TCDS -40
https://rgl.faa.gov/Regulatory_and_...B2EF55D312BB0FCD8625768700528381?OpenDocument

Current DER listing:
https://www.faa.gov/other_visit/avi...gations/designee_types/media/DERDirectory.pdf
Click to expand...

You are correct that there are two different type certificates. I forget the reason. However MHIA is very supportive so I think they would help with supporting data, at least to some extent.

Kenny Phillips said:
I believe that you have one step beyond getting the DER (hard for me not to type RCE, ya know!) to sign off. Not many field approvals are being granted lately, it seems. If you are going to develop a saleable STC for the increased altitude, it may be worth it (and it may be worth finding out if the airframes are truly identical, so that perhaps the outflow valve, etc. could be upgraded to get higher differential).
Click to expand...

In my day job DERs have a bit of a different role. I’ve talked to independent DERs who have claimed that submitting their paperwork with a 337 will be approved. I talked to one DER about replacing the air conditioning compressor in the 414 with a much lighter weight (all electric) model and he said once he worked through his bits and gave me the paperwork I just needed my shop to install and file the 337.

However I never did that so I don’t know if he was blowing smoke. I do know that we used a DER to design and approve a repair on the Aztec when the wing skin cracked, and that was accepted, but this is different.

Doc Holliday said:
What sort of emergency oxygen do you have for the cockpit and the cabin in the MU-2?
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Standard masks for pilot and copilot. I forget what’s in back since I’m not there much and I don’t know if that is different on later planes.
 
Also I doubt I would want to bother with an STC. Frankly I think the market is minimal. Really just wanting approval for this plane.
 
Under Part 25, which is for transport category there is this:

25.841 Pressurized cabins.
(a) Pressurized cabins and compartments to be occupied must be equipped to provide a cabin pressure altitude of not more than 8,000 feet at the maximum operating altitude of the airplane under normal operating conditions.

(1) If certification for operation above 25,000 feet is requested, the airplane must be designed so that occupants will not be exposed to cabin pressure altitudes in excess of 15,000 feet after any probable failure condition in the pressurization system.

(2) The airplane must be designed so that occupants will not be exposed to a cabin pressure altitude that exceeds the following after decompression from any failure condition not shown to be extremely improbable:

(i) Twenty-five thousand (25,000) feet for more than 2 minutes; or

(ii) Forty thousand (40,000) feet for any duration.
 
That makes sense for part 25. I’m not sure if part 23 has something like that (specifically applying to class 3 aircraft in this case).
 
Ted DuPuis said:
That makes sense for part 25. I’m not sure if part 23 has something like that (specifically applying to class 3 aircraft in this case).
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Agreed. If I have more time I'll research it.

I believe your MU-2 was certified under the CAR's.

Certification basis
CAR 10 dated March 28, 1955. (Applicable regulations are CAR 3 dated May 15, 1956
including Amendments 3-1 through 3-8, plus the Special Conditions stated in FAA letter to
the JCAB dated May 14, 1965, modified by FAA letters to the JCAB dated January 25, 1968,
and May 12, 1971.
Type Certificate No. A2PC issued November
4, 1965.
Application for Type Certificate dated
November
25, 1964.
 
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Ted DuPuis said:
Really just wanting approval for this plane.
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Why not a one-time only STC? Not as complex. We did one that changed various structural airframe loading limitations and aircraft operating limits for a B212 to install some equipment for an EPA contract. I believe the ACO or MIDO recommended the Structures DER, who gave us the Flight Test DER. This was somewhat similar to your project??
 
dtuuri said:
Trading for a 690B comes to my mind.
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Being realistic about the value of this plane vs a comparable 690B (as well as operating cost differences) that isn’t a good option. Plus the 690 won’t fit in the hangar and I did not enjoy flying them.

Bell206 said:
Why not a one-time only STC? Not as complex. We did one that changed various structural airframe loading limitations and aircraft operating limits for a B212 to install some equipment for an EPA contract. I believe the ACO or MIDO recommended the Structures DER, who gave us the Flight Test DER. This was somewhat similar to your project??
Click to expand...

That could be a viable option, not something I’d considered.
 
Ted DuPuis said:
Being realistic about the value of this plane vs a comparable 690B (as well as operating cost differences) that isn’t a good option. Plus the 690 won’t fit in the hangar and I did not enjoy flying them.
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You wouldn't have to cross your legs to make coordinated turns anymore. :) Besides, the 690B I flew didn't fit in the hangar either, so the engineers modified a lawn tractor to lift the nose gear, thus lowering the tail enough to get under the door overhang when I pushed it in. I loved flying it. The single engine performance was better than the Citation we replaced it with. Max operating altitude was FL310. What didn't you like about it?
 
dtuuri said:
You wouldn't have to cross your legs to make coordinated turns anymore. :) Besides, the 690B I flew didn't fit in the hangar either, so the engineers modified a lawn tractor to lift the nose gear, thus lowering the tail enough to get under the door overhang when I pushed it in. I loved flying it. The single engine performance was better than the Citation we replaced it with. Max operating altitude was FL310. What didn't you like about it?
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In my case the 690 wouldn’t fit in the hangar by any dimension and would require a communal hangar, so that’s a negative.

I didn’t like the column for the controls and on long trips found that restricted my ergonomics enough to be uncomfortable. Taxiing it was ridiculous, the hydraulics for the nose gear I found dumb at best. I didn’t like the control harmony (so to speak). It was unrewarding to hand fly, much like the 414 was. The MU2 I love hand flying and almost never use the autopilot.

On the plus side a 690 would have a better layout for dog crates.

But again, if I look at realistic resale values, this MU2 is worth at least a couple hundred grand less than a similar 690 with -5s, which is not a delta we could swing. Operating costs? The highest shop visit for the MU2 so far has been $17k and that’s at a service center with extra work done for a 100/200/600. I haven’t heard of people paying close to that little for inspections on 690s, unless maybe it was a Grand Renaissance that got completely redone and then also cost a whole lot more to buy.

If someone wants to donate one it’d be another story but even then I’m not convinced that the math would make sense to switch aircraft. If someone donated a Solitaire or a Marquise (and that would solve my altitude problem) it’d be different, but I don’t see that happening, either.
 
Ted DuPuis said:
In my case the 690 wouldn’t fit in the hangar by any dimension and would require a communal hangar, so that’s a negative.

I didn’t like the column for the controls and on long trips found that restricted my ergonomics enough to be uncomfortable. Taxiing it was ridiculous, the hydraulics for the nose gear I found dumb at best. I didn’t like the control harmony (so to speak). It was unrewarding to hand fly, much like the 414 was. The MU2 I love hand flying and almost never use the autopilot.

On the plus side a 690 would have a better layout for dog crates.

But again, if I look at realistic resale values, this MU2 is worth at least a couple hundred grand less than a similar 690 with -5s, which is not a delta we could swing. Operating costs? The highest shop visit for the MU2 so far has been $17k and that’s at a service center with extra work done for a 100/200/600. I haven’t heard of people paying close to that little for inspections on 690s, unless maybe it was a Grand Renaissance that got completely redone and then also cost a whole lot more to buy.

If someone wants to donate one it’d be another story but even then I’m not convinced that the math would make sense to switch aircraft. If someone donated a Solitaire or a Marquise (and that would solve my altitude problem) it’d be different, but I don’t see that happening, either.
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I can't tell you how to squeeze one into your small hangar or pay for one (I sold our 1977 690B in 1984 for $390K), but I CAN tell you how to steer with the hydraulic nose steering/differential braking system: Don't listen to anybody else! The conventional wisdom is to block the rudder with your legs and use your toes to modulate the brake pedals for steering. Nah, don't do that. My feet wouldn't easily bend back enough to avoid uncommanded steering inputs. So, I learned to let the rudder pretty much have its way and only use one foot at a time, the other one completely off the pedals. Worked great. I'm not an autopilot junkie either, so I find it interesting you didn't like to hand-fly the 690B. I only steered the MU-2 around once, IIRC, and I thought IT was a mess! YMMV, I guess.
 
dtuuri said:
I can't tell you how to squeeze one into your small hangar or pay for one (I sold our 1977 690B in 1984 for $390K), but I CAN tell you how to steer with the hydraulic nose steering/differential braking system: Don't listen to anybody else! The conventional wisdom is to block the rudder with your legs and use your toes to modulate the brake pedals for steering. Nah, don't do that. My feet wouldn't easily bend back enough to avoid uncommanded steering inputs. So, I learned to let the rudder pretty much have its way and only use one foot at a time, the other one completely off the pedals. Worked great. I'm not an autopilot junkie either, so I find it interesting you didn't like to hand-fly the 690B. I only steered the MU-2 around once, IIRC, and I thought IT was a mess! YMMV, I guess.
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I flew with people who had thousands of Commander hours and told me once I got used to it it was “better”, and found they didn’t do any better than me. :)

But I did not try your method. I’ll try to remember that if I fly one again.

And yeah, most people think I’m nuts for not liking how Commanders fly, which is fine, we all have our own preferences. I just know I didn’t like it at all.
 
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