SID Formation Data...?

[Ernie Martin]

I can help with your first three questions:

#1: No. As you point out, no finite-element structural analysis of the aircraft was done or is planned. My guesses: at best Mr. Oliver is misinformed, at worst he carefully crafted his statement to make 2 accurate but unrelated statements and hope that the reader think they are connected (read the statement again: 1. Cessna is proficient in fatigue analysis; 2. the twin-boom design of the 336/337 has higher loading; it doesn't say that there was analysis).

#2: Cessna does not have a labor estimate and asked the user community to provide one.

#3: After considerable scrutiny of the SDRS data it appears that N2FOR was the N-number designation used by one facility for any foreign-registered aircraft SDRS. That N-number appeared in several Skymaster SDRS with different serial numbers, all serviced by the same facility. A more comprehensive search of all SDRS found the same N-number used by that facility for other aircraft (Pipers, Boeings, Lears, etc.). It caught your attention because this Skymaster was the only one with a wing-attach SDRS, but note that the service was in 1976 on a relatively new 337G with 570 hours, so clearly not a fatigue issue.

Ernie Martin

[Skymaster337B]

Sounds like "they" want me to believe that Cessna had no idea about high loading from the tail booms during the design. Give me a break. I bet the engineers with slide-rules back in the 60's knew more about design and fatigue/loading then the guys working at Cessna today -- using their "Proprietory/Trade Secret Analysis" i.e., some computer model. I bet they're using the same computer model the U.N. is using to prove global warming.

My point. I think Cessna should collect (purchase) a random sample of high hour Skymasters and analyze the wing mounts. Then let us know if there really is something to worry about or not. I hate it when they create a boogie-man.

[Dave Underwood]

So let me understand the situation here.

Cessna has taken a single SDR for wing attach fittings from a low time 337G in 1976 from a foreign maintenance organisation on a ficticous aircraft N2FOR and on the basis of that figures the entire fleet is at risk?

OK, I suppose I have heard stranger things.

As for the twin boom loads, if you look at the the design, they had that one all figured out. In fact in that time frame they were doing FEM analysis (Finite Element) and should still have the results of that. Is it worthwhile trying to ask some one at Cessna?

As for the SDR, if you can send me the European operator's name and details, maybe I can get a bit more information as I am still here in Europe. The reason for asking is 337's were a pretty small group here in Europe and there may well be some recoverable history.

What were the particular serial numbers of the aircraft involved? If those aircraft are still around, maybe we should have a look at them or pay an engineer to have a look at them. If those aircraft are no longer on the N register, it would be worthwhile finding out where they are now. There may even be historical paperwork which lead to the filing of the SDR.

The other thing to consider is that Cessna kept records by serial number of build history and build issues. If we have the serial number data, there might be information there. I know they did this as the leading edge skins and position of the stall warning system were not in the correct place per the manual due to a factory approved production change for my aircraft only.

I am more than willing to try and locate what I can. Please let me know.

Regards - Dave

[Ernie Martin]

On the idea of Cessna checking several high-time Skymasters for wing-attach problems, there's no need. Don Nieser's Commodore Aerospace has done it as part of their restorations and found none.

On Dave's idea of tracking the fairly new aircraft with the single wing-attach SDR, it's serial number 01633. The facility may not be in Europe. For those of you eager to look at the Skymaster SDRS, you may find them at www.consultresearch.com/337SDRSC7.html arranged by area of the aircraft (the single wing-attach SDR is the fifth in the Wing section).

Keep in mind that thse SDRS may be the result of hard landings or manufacturing defects. You need to analyze the data carefully, then go to the Form 337 database to see if there were prior accidents, but some are not reported. In this case, the newness of the aircraft (a 337G inspected in 1976 with 570 hours) says it all.

One final thought as to why this SID exists, and please allow me some editorial license: since the 400-series aircraft had problems in the wing attach areas (including an in-flight wing separation) and since separation of a wing is the aircraft structural engineer’s worst nightmare, Cessna chose to include a wing-attach SID for Skymasters. The inclusion ignores the vast differences in loading between the low-wing 400-series and the high-wing Skymaster, the massive over-design of the Skymaster wing-attach area, and the absence of any fatigue problems in many disassembled high-time aircraft.

So it seems sort of knee-jerk reaction. There are compelling reasons for excluding it -- it is unnecessary, its cost threatens to ground many aircraft, and it actually increases the risk of Skymaster accidents -- but to date Cessna won't budge.

Ernie Martin