Incident Summary
During preparation for landing, the flightcrew selected the landing gear handle to the down position, but the gear did not extend electrically. The crew followed the abnormal checklist, which included using a mechanical hydraulic pump, but the landing gear remained retracted. The flightcrew subsequently landed the airplane with the gear retracted.
Findings
Examination of the landing gear system revealed that maintenance personnel had improperly installed the landing gear service valve six days prior to the incident. The installation error involved reversing two hydraulic lines. The reason for the electrical malfunction of the landing gear service valve could not be determined.
Maintenance Manual
The airplane's maintenance manual did not include a requirement to cycle the landing gear, either mechanically or electrically, after replacement of the landing gear service valve.