Cessna C337 SID

[skymstr02]

Originally Posted by tropical

Yes you can delineate it. Separate by O-2, 336 and civilian 337. It's not a matter of "exclusion" but rather model. And it's a known fact the O-2's lived a harder life and also had wing hard points.

What I'm saying is that some civil registered 337's may have experienced the same stresses that an O-2 has. If you are not the original purchaser from Cessna on your aircraft, you do not know what kind of stresses have been accumulated on the airframe. i used to work on a 337G, N200ZF, that was a fish spotter. It had a 175 gal fuselage fuel tank to give it 22 hour endurance. It was not uncommon for that airplane to take off at 6100 lbs, and seven leg it from Houston to Cape Town South Africa. What kind of stresses have been placed on that wing structure?

Fatigue is cumulative on aluminum and it doesn't matter if Lt. Hamfist or commercial pilot Hamhand is at the controls.

O-2A wings are different from 337 wings, as there is additional structure on the rear spar to absorb the firing loads from the hard points. The wing spars and center carry thru spars are also physically larger than its civillian cousins. Even the wing attach bolts are two sizes larger than its 337 counterpart. An O-2 wing will not mate up to a civil fuselage.

There's no way that a prudent engineer could simply dismiss a portion of the population just because if was never in military service.

[WebMaster]

Originally Posted by skymstr02

What I'm saying is that some civil registered 337's may have experienced the same stresses that an O-2 has. If you are not the original purchaser from Cessna on your aircraft, you do not know what kind of stresses have been accumulated on the airframe. i used to work on a 337G, N200ZF, that was a fish spotter. It had a 175 gal fuselage fuel tank to give it 22 hour endurance. It was not uncommon for that airplane to take off at 6100 lbs, and seven leg it from Houston to Cape Town South Africa. What kind of stresses have been placed on that wing structure?

Fatigue is cumulative on aluminum and it doesn't matter if Lt. Hamfist or commercial pilot Hamhand is at the controls.

O-2A wings are different from 337 wings, as there is additional structure on the rear spar to absorb the firing loads from the hard points. The wing spars and center carry thru spars are also physically larger than its civillian cousins. Even the wing attach bolts are two sizes larger than its 337 counterpart. An O-2 wing will not mate up to a civil fuselage.

There's no way that a prudent engineer could simply dismiss a portion of the population just because if was never in military service.

You are absolutely correct. And when we ask if your airplane is used for low level work, even then we are not getting a good picture of what that means.

Take for example someone doing fire spotting, where they are making tight turns, maneuvering at low altitudes, with lots of thermals. At the other end of the spectrum, some one who is doing polar bear tracking, where, they are flying over a non-thermal environment, basically straight and level, though at a low altitude.

You can't simply say 0-2's had higher stresses. I would argue that the fire spotter gets more stresses, on a continuing basis, than most of the 0-2's in civilian service. Remember that the 0-2's that were beat up pretty badly were simply scrapped.

When you buy a plane, and you look at the log books, you can't tell what kind of use the aircraft had. My former aircraft had lots of hours, but it was a all used as a corp plane for a collection of companies, and for a number of years, was flying every day.

[tropical]

Originally Posted by larry bowdish

You are absolutely correct. And when we ask if your airplane is used for low level work, even then we are not getting a good picture of what that means.

Take for example someone doing fire spotting, where they are making tight turns, maneuvering at low altitudes, with lots of thermals. At the other end of the spectrum, some one who is doing polar bear tracking, where, they are flying over a non-thermal environment, basically straight and level, though at a low altitude.

You can't simply say 0-2's had higher stresses. I would argue that the fire spotter gets more stresses, on a continuing basis, than most of the 0-2's in civilian service. Remember that the 0-2's that were beat up pretty badly were simply scrapped.

When you buy a plane, and you look at the log books, you can't tell what kind of use the aircraft had. My former aircraft had lots of hours, but it was a all used as a corp plane for a collection of companies, and for a number of years, was flying every day.

By lumping O-2's into the mix with a civilian 337 you are asking for trouble. The FAA is not the smartest operation around and they tend to go with the worst case scenario. Back years ago the FAA issued a wing demating for PA28 and PA32 airplanes because a PA32 shed a wing in flight. But if one looked into the circumstances the plane that created the AD was flown in Alaska, off of rocky strips carrying cargo (overweight).

You are relying on the benevolence of the FAA. Look at it this way, this is a negotiation. You don't go in with what you feel is adequate. Go in with a lot more conditions because I will guarantee you they will cut them down to get right to the point. Unless you guys want to wind up with a cost prohibitive AD on these planes you better be careful. Cessna would love to get rid of all these old planes and the corresponding liability and the FAA would be all to willing to help them.

[Ernie Martin]

Please note that I've added a 6th poll to determine how often you fly with a cabin load which is roughly half the maximum. Sorry we didn't post this with the earlier polls.

Ernie

[Roger]

My original post was meant to discuss the possibility that the extreme use (and possible operations outside of the normal envelope due to military use) of 02's could perhaps cause harm to the data set used by the FAA. This has then brought up the question of operations of 336/337's in environments that are also outside of "normal".

The better question would perhaps be: If a 336/337 or 02 was used in a category other than "normal" and or was used under 91.323 in Alaska allowing for heavier gross weight, should it be used in the data set?

For precedent, the FAA should be asked if the 400 series data that was used to predicate the AD included aircraft that were "known" to have exceded their "normal civilian" operating parameters. If the answer is no, then clearly the FAA should not use 336/337-02 aricraft that were knowingly operated outside of the aircrafts civilian standard operating envelope and weight limitations.

Of course there are aircraft that have been operated outside of their normal envelope on "occasion or by accident" but that is something that would be virtually impossible to know. However if the non-standard operations are known, those aircraft should be excluded with out question.

[edasmus]

Thanks for the info Ernie. Just out of curiosity, do you have any idea if the FAA is looking into SID's for aircraft manufactured by someone other than Cessna or are they singling out Cessna for some reason?

[Ernie Martin]

No idea, but my guess is that all the manufacturers have been tasked and funded to do the same.

Ernie

[Ernie Martin]

We had a productive meeting with Cessna yesterday. There were 9 people from Cessna and these 7 guests/users: 3 owners (Steve Keller, Steve Walz and me, all very familiar with the aircraft), 2 from Commodore Aerospace (Don Nieser and his structures person, Larry Good) and 2 from AirScan (which operates 23 late-model Skymasters).

For context let me mention that this SID exercise is FAA driven and is expected to be followed by similar exercises for other Cessna aircraft models.

Here, in brief, are my impressions:

1. Cessna has been working on this for roughly 6 months or more. Some of the documents date to March and some of the Cessna people at the meeting visited Steve Keller about 6 months ago to get a first-hand look at his airplane (most of these people were unfamiliar with Skymasters because they were not around when they were designed, built and tested, and Cessna does not have a significant database of experience with the aircraft).

2. Unlike the 400-series SID program, this is an experience-based, not analytically-based program. No finite-element structural analysis of the aircraft is planned. Instead, the Cessna people went to the FAA's Service Difficulty Reports (SDRS) database and used that as the basis for the proposed SIDs. At the time of the meeting, Cessna had written draft SIDs and the meeting was in part intended to get the users’ inputs on these proposed SIDs.

3. Approximately 23 proposed SIDs were reviewed, some in more detail than others.

4. For some, the guests were surprised by, and expressed disagreement with, the area in question and/or the initial compliance requirement (for instance, 7,500 hrs or 20 years).

a) As an example, one may call for an inspection for cracks in a wing area where none of the users have ever seen a crack, either on very-high-time aircraft or aircraft that have seen high-load accidents, yet there were no SIDs for other areas of the wing which are susceptible to damage due to fatigue or excessive loads.

b) Or one may call for inspection at 20 years (from manufacture) when it’s a fatigue (not corrosion) issue, so that an aircraft which has sat in a hangar since manufacture and never flown would be subject to this SID looking for fatigue cracks. Or the SID may call for an inspection requiring massive aircraft disassembly even if there is no corrosion evident in easy-to-inspect adjacent/comparable areas.

5. As a result of these user comments, Cessna agreed to look more closely at the SDRS data (some of which are 15 – 20 years old) to try to determine whether they may have come from questionable aircraft or sources (e.g., an aircraft which may have had an earlier accident and/or improper repair) or misidentified the aircraft or part. Inquiries I performed after the meeting suggest that FAA SDRS data is generally considered suspect in the aircraft maintenance business. If true, then Cessna’s re-examination may bear fruit.

6. Moreover, Don (a retired Air Force Lt. Col. who has over 20 yrs experience with our aircraft, worked for years on aging aircraft and corrosion research for the Air Force, has disassembled and restored dozens of Skymasters, and has many Skymaster aircraft and parts which Cessna can examine) invited Cessna to visit him and see first-hand why he believes that some of the proposed SIDs need re-examination. Roughly, his words were “When you see this item, especially one removed from a high-load, high-fatigue aircraft, you’ll see right away that this item can’t fail that way, that other parts will fail first, that the SDRS data must be from a suspect aircraft or refer to a different part”.

7. Cessna also agreed to re-examine the initial compliance requirements, including the possible removal of years-since-manufacture requirement.

8. We were asked to estimate the manpower requirement for each SID.

9. I don’t have at this point a schedule of future activities. There wasn't enough time to review all of the proposed SIDs, so we are continuing their review. We talked about the next meeting of this group perhaps held both in person and as a WebEx Internet meeting. With the caveat that all of these points are my impressions, I believe that such a meeting will likely come after we have submitted our views on the unreviewed SIDs and after points 4 – 6 above are addressed. I’m hoping that Cessna goes to Don’s shop (it’s a 3 hour drive) and that Don (and perhaps AirScan and others) can furnish point 7 after that. I expect to contact Cessna and hope to get a better feel for future activities.

In summary, there are some issues that we’re all working through, but I found the Cessna people competent, professional and receptive to considering our points. The attendance of Don and Larry was crucial and I hope that they can continue contributing.

Ernie