<p><strong><font color = "blue">Sigma-Tek Air Pump: 1U478; Faulty or Broken Drives, (5 ea); ATA 3710</font> </strong></p>
<p><em>(An FAA Principal Maintenance Inspector submitted five hard copy discrepancies reports of this engine driven, dry air pump. Essentially similar as discrepancies—same ATA code—the following is a composite of the group. </em></p>
<p><em>Served aircraft are all Grob G120A's sporting Lycoming AEIO-540 engines.)</em></p>
<p>A repair station submitter writes, “During engine start suction pressure was reading zero. During further trouble shooting the technician found the engine driven dry air pump had a broken shaft <em>(two aircraft </em>). Probable cause could be from vibration or hard start. <em>(Part time listed as 194.0 hours.)”</em></p>
<p>Another report states, “The pilot reported suction was below limits and the aircraft returned to base. Upon troubleshooting the mechanic removed the air pump and noticed the shaft was very easy to rotate—it had no resistance to it <em>(three aircraft </em>).” </p>