The pilot reported that, shortly after the skydiving flight departed, the Cessna 210’s engine experienced a “mechanical failure,” so he made a forced landing in a farm field south of the airport near Sussex, N.J.
The airplane nosed over in the mud, which resulted in structural damage to the airframe.
During a post-accident test run of the engine on the airframe, lower-than-normal exhaust gas temperature indications were observed on the engine’s left-side (Nos. 2, 4, and 6) cylinders. Excessive soot and smoke were also observed on the engine’s left side.
During a subsequent test run, the engine initially did not achieve full power. Further examination revealed that both of the No. 2 cylinder intake valve springs were fractured, and visible rust was observed on the surfaces of the springs.
The springs showed evidence of fatigue fractures that had originated from rust pits on the fracture surfaces.
After the valve springs were replaced, the engine was capable of operating normally at full power.
An annual inspection was completed on the engine less than two months (13 engine operating hours) before the accident. As part of the annual inspection, the engine manufacturer’s operating manual required the removal of the cylinder rocker covers and inspection of the valve area for breakage and proper lubrication.
It is likely that maintenance personnel did not adequately inspect the No. 2 cylinder valve area during the annual inspection, which allowed the rust to go undetected and resulted in the in-flight failure of the No. 2 cylinder valve springs.
The NTSB determined the probable cause as maintenance personnel’s inadequate inspection of the No. 2 cylinder valve area during the most recent annual inspection, which resulted in the in-flight failure of the intake valve springs due to rust on the spring surfaces and subsequent fatigue cracking.
NTSB Identification: ERA15LA071
This December 2014 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Well, there aren’t many aircraft engines (Hall Scott, OX 5/9), built now that have “open valve/spring and stems”, so maybe I will jump forward 80 years.
Corrosion in the cylinder heads is formed by moisture condensation under those valve covers or introduced by an “air oil separator” a popular STC offered by several companies during the last three decades.
I have never taken off valve covers on engines unless there was a problem suspected or directed by SB’s or AD’s. I have seen dropped valves on more Lyc engines than Cont. which get more than their share of stuck valves (reason to remove valve cover).
The inspection was not arbitrary:
“As part of the annual inspection, the engine manufacturer’s operating manual required the removal of the cylinder rocker covers….”
A&Ps and IAs chime in here but I believe you are supposed to have the service manual open to the section that covers the work you are performing.
I guess that is why they write these pesky maintenance manuals??
To prevent stuff like this.
This is also why I am not an A&P.
I have pointed this out to a few A&Ps and they laugh when I bring it up.
I bet this guy or guys aren’t laughing.
“maintenance personnel’s inadequate inspection of the No. 2 cylinder valve area during the most recent annual inspection”
?????
Since when was inspecting the valve springs part of routine maintenance inspection criteria? If there is no cause to inspect the valve springs, who would arbitrarily remove all the rocker covers, and possibly even remove all the springs to perform a corrosion inspection? Where do we draw the line? Was the cylinder removed or repaired during the previous inspection?
Perhaps there are some details missing from this article that would add some clarity to this.
This is a sky dive plane. Those planes are flown a lot, which makes rust on the valve springs a real mystery. On a routine annual, I wouldn’t be pulling the valve covers on a plane that is in the air a lot. Maybe the skydive club had just bought this plane after it sat for a few years as a ramp queen??? If so, then a closer look may have been warranted.
But the article doesn’t clarify. Also, in the NTSB Full Narrative, the NTSB investigators and their hired mechanic tried to troubleshoot the engine and couldn’t find the problem. It was shipped back to the manufacturer where they also spent a lot of time attempting to diagnose the fuel system before the failing valve spring was finally discovered. So this was something that was not so obvious to either the investigators mechanic, or the manufacturer’s experts. So laying the problem at the fault of the local mechanic that performed the annual is bogus.
As far as I know, Lycoming require a rocker box inspection every 400 hrs; but I think the 210 has a Continental.
I guess the good news is they can’t blame it on the dead guy.
Thank you again to general aviation news. I read these synopsis (sp ? ) every day. Rusted valve spring on #2.
Another failure mode for me to be aware of while I’m up there. The longer I read these articles, the longer that list gets.
I have a book called “the repair of modern aircraft ” published in 1918 ,this does go into inspecting valve springs and rockers on a “daily” basis.
This may be of some help.
Tony