[Paul462]

Mike Busch, author of Cessna 400-Series Wing Spar Update, and who had considerable involvement in that situation, has this to say:


Paul, I'm not sure why you're so concerned about this. The Cessna SIDs have no regulatory impact in the US, except possibly for Part 135 operators who have committed to comply with service bulletins in their op specs. (I don't think there are a lot of 337s in Part 135 service.) We've seen absolutely no evidence that the FAA intends to mandate any of the SIDs via Airworthiness Directive, except for the 400-series twins where they've already done so. It looks to me as if Cessna ultimately will issue SIDs on all their piston GA aircraft. The FAA is not involved in this: SIDs are essentially giant service bulletins issued unilaterally by Cessna without FAA involvement or concurrence. Unless the FAA makes some radical course change, Part 91 operators can simply ignore the SIDs. Unless you're aware of some actual safety-related aging-aircraft issues with the 337 that could trigger FAA rulemaking action, I would not lose any sleep over this.

The situation is different in some other countries, where the local CAAs require Part 91 operators to comply with the SIDs. The Cessna SIDs program has been a real disaster for owners in Australia, for example. But in the U.S., it has been more or less a non-issue (except for the 401/402/411/414 aircraft affected by the spar-strap AD).

I don't think it's worth trying to oppose the SIDs unless the FAA issues an SAIB or NPRM that suggests they are planning to mandate any of them. In the absence of such a signal from the FAA, making a big deal over the SIDs can only be counterproductive by focusing FAA attention on the subject. My thoughts, for what they're worth.

Best...Mike


We asked Mike about the reasons that the 337 SID may not come back to haunt us as an AD, and he responded:


The 400-series spar-strap ADs were triggered by a series of unfortunate events and decisions.

There was a fatal accident in a 402C where the wing came off in flight. The airplane had 20,000 hours, and the NTSB investigation revealed that the origin of the spar fatigue failure was a pre-existing flaw in the spar that was there when the aircraft originally rolled out of the Cessna factory. In addition, the aircraft had previously had a hard-landing incident that tore a main gear leg out of the wing and overstressed the spar beyond design limits. Despite both of these problems, the airplane flew 20,000 hours before the wing came off. This was a one-time freak accident, but it put the 402 on the FAA's radar screen anyway -- specifically the aging aircraft folks (notably Marv Nuss) at the FAA Small Airplane Directorate in Kansas City. That is never a good thing.

Then, the FAA became aware of some spark cap cracks (not failures) in a few old high-time tip-tank 402s that had been in Grand Canyon sightseeing service, and had been operated at an extreme corner of the loading envelope with extremely heavy cabin loads and extremely light fuel loads in turbulent conditions, thereby placing tension stresses on the lower spar cap far in excess of what is ever experienced in airplanes operated with more normal cabin and fuel loads. (I strongly suspect that these aircraft were operating over-gross, but of course can't prove it.)

Under the circumstances, an AD mandating lower spark cap reinforcement for the 402 was inevitable. We tried very very had to persuade the FAA to limit the scope of the AD to the 402, because no other 400-series twin has ever exhibited any spar cracking and no other 400-series twin operates in the extreme corner of the loading envelope that these 402s did. Despite our best efforts, the FAA rejected our arguments and issued a spar-strap AD that affected 401s, 411s and 414s, none of which had ever exhibited any problems because they're never operated in the extreme loadings that the problem 402s used. Owners of those models were unfortunately caught in the crossfire over the 402 spar issues, and I feel bad that we were not able to prevent this (and heaven knows we tried).

Unless and until actual cracks or other clear safety-of-flight issues appear in other Cessna models (and I sincerely doubt that they will), I see no reason for the FAA to consider ADs against 300-series Wallace twins, Skymasters, or Centurions..

I don't have a crystal ball, so I could be wrong. I hope not.

Best...Mike



Thanks for the input, Mike!