Squawk Box

The aft canted bulkhead (p/n 2612060-5) at station 474.40 was discovered with two cracks, each approximately 1.5 inches in length. During removal, other damage was found. Both vertical stabilizer webs (p/ns 2631021-15 and 2631022-2) were replaced because of significant fretting, as was the aft bulkhead assembly (p/n 2612059-1).

During inspection, the forward upper l/h wing attach point was found to have corrosion on the wing attach fitting (p/n 08113507). After removing the upper wing-fuselage fairing, inspection revealed intergranular corrosion on the fitting, and severe rust on the mounting bolt heads. The fitting was replaced due to the severity of the corrosion. Probable cause of this corrosion is the fuselage-wing fairing not being sealed properly in the area above the fitting.

The bulkhead (p/n 0450046-5) was installed in 2007 at 1476.4 flight hours and has been inspected each 100 hours since. At the latest inspection, a crack was discovered at the base of the propeller hub; after removing the hub, severe cracking was found, comprising 85 percent of the distance around the center of the bulkhead. Mandatory propeller removal should take place at least every 200 hours of operation for a more thorough inspection of the bulkhead.

During an annual inspection, the right ruddervator trim control cable was found routed incorrectly and cutting through the right ruddervator control tube approximately 75 percent. The tube also had signs of a crack originating from the damaged section of the tube (cut area), and had begun to bend as a result of weakening. There were no maintenance entries noted in the logbook to determine when this may have occurred.

During an annual inspection, technicians found the l/h elevator balance weight (p/n 96-610022-7) detached from its mount. The r/h elevator balance weight was found both broken and loose on its mount. The detached l/h weight was able to shift position inside the elevator and cause an out-of-balance condition. This damage appears to be caused by vibration.

When a new rear wing strut was received from the manufacturer, there were two longitudinal cracks in the strut in the electrically welded seam of the seamless strut tubing one foot from the upper wing strut fitting. The defect is obviously due to the tubing manufacturing process and not by secondary operations or weldments. It is likely the entire batch of raw tubing has multiple defects and should be located and inspected. It is also likely this batch of tubing was disseminated to multiple customers in addition to the manufacturer.

Inspection of the sidewall structure revealed a failed crosstie at fuselage station 227.125. The part cracked fully in two pieces and is deformed from its original flat shape, apparently from compression. Two rivets immediately above the break have failed. No other crossties (p/n 101-420013-1122) display any deformation, cracking or evidence of preload.Part Total Time: 8186 hours

Engine oil was observed dripping out of the port side wing root. The ¼-inch aluminum oil pressure line (p/n 5600107-11) was routed over the top of a section of three-inch SCAT tubing. The SCAT tubing’s wire chafed a hole in oil pressure line. This airplane’s starboard line also was routed the same way and was rerouted to prevent chafing.

The nose landing gear failed to extend when the gear was lowered for landing-a nose-gear “up” landing followed. Examination revealed the uplock bellcrank forward arm (p/n: 204303112) was bent and cracked through 90 percent of its material. It would not allow the uplock to disengage. The probable cause: severe side loading during landing at an unknown time. A new part was installed and a gear-rigging check made. No other problems were noted.

The pilot reported a burning smell in the cabin. Inspection revealed the taxi light circuit breaker switch had burned internal components. This switch (p/n 35-380132-105) is the improved model required by AD 2008-13-07. Unfortunately, when these switches overheat, it can be impossible to determine if the insulators had been installed improperly, or installed at all. This was the second post-AD switch failure in this fleet.