Squawk Box: 01/06


Cessna 150M
Cracked Engine Mount

A mechanic found the R/H lower engine mount tube cracked. The crack is located within one inch of the nose wheel strut support. This crack is -inch in length, moving around the circumference of the tube. The mount (p/n 0451120-1) was replaced.Part Total Time: 5002.1 hours.

Cessna 172
Cracked Rear Wing Spar

A crack was found in the rear wing spar. A search of the SDRS database found three airplanes where cracked spars were detected. The total time in service (TIS) for these three airplanes ranged between 12,000 and 16,000 hours. The cracks are hidden between the lower skin and the flap track support rib. Use of a magnifying glass and a bright light or Borescope will assist the inspection.It is recommended the rear wing spar be thoroughly inspected at the next regularly scheduled inspection on airplanes with 12,000 or more hours TIS.

Cessna Model 550 Citation
Defective Autopilot Servo Drive

The crew reported that the controls were stiff in the roll axis. (While in flight…) the autopilot was turned off and the circuit breaker cycled with no change in the condition. After landing without incident, technicians trouble-shot the autopilot system. They discovered the aileron autopilot servo drive clutch (p/n 4006719-906) was not fully disengaging, causing the excessive force required to roll the aircraft. The aileron autopilot servo drive was removed and replaced. Both ground and in-flight operational checks were performed and no defects noted.Part Total Time: unknown.

Continental IO-520C
Cracked Cylinder Heads

An operator describes the cylinder heads he found cracked by compression testing during a 100-hour inspection: We are using a soap solution to detect cracks in the exhaust side of the cylinder while doing the compression checks. We are performing compression checks every 50 hours. Three cracked cylinders were found on the same engine at this inspection.Cylinder assembly part number noted as: TISN71.2ACA. Head cracks near the exhaust valves for cylinders 2, 4, and 6 were listed in this report. A second report on this aircrafts R/H engines number 3 cylinder was also found cracked, having 1851.0 hours. This operator describes cracking cylinders as an ongoing problem for his fleet of aircraft.Part Total Time: 400.0 hours.

Lycoming IO-360-C1C6
Failed Cylinder Stud

A mechanic gives his idea of why a cylinder attach stud failed: (I believe…) the probable cause is metal fatigue due to the age of engine crankcase studs, and the number of cylinder removals and replacements during the engines lifetime. This aircraft has spent most of its life as a training aircraft.Prevention: thorough inspection of and/or replacement of cylinder base studs during engine overhaul, with mandatory replacement time periods or cycles.Part Total Time: unknown.


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