NTSB Identification: CHI08IA065.
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Nonscheduled 14 CFR operation of Ameristar Air Cargo, Inc.
Incident occurred Tuesday, January 08, 2008 in Lincoln, NE
Probable Cause Approval Date: 07/30/2008
Aircraft: Boeing 737-2H4, registration: N733TW
Injuries: 38 Uninjured.

NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.

Two days before the incident flight, the airplane was placed in maintenance for a "[Left/Hand Main Landing Gear] swivel valve leaking." The corrective action was accomplished by one of the operator's mechanics. The mechanic reportedly removed both the swivel valves on the left main landing gear. The aft swivel valve was removed and replaced with a new valve. The forward valve was removed and reinstalled. That valve was checked for leaks and the airplane was returned to service prior to the incident flight. The airplane, on a non-scheduled domestic passenger flight, was taxiing after landing, exited the taxiway, and became stuck in snow and mud despite the pilot's attempts to maintain directional control. The captain reported a total loss of all hydraulic systems. The airplane's maintenance manual 32-41-61 contained a warning that stated, "WARNING: MAKE SURE THAT THE SWIVEL JOINT AND HYDRAULIC LINES ARE ORIENTED AS SHOWN ... . THE HYDRAULIC LINE TO THE BRAKE ASSEMBLY MUST BE CONNECTED TO THE SWIVEL HOUSING AND THE HYDRAULIC LINE FROM THE ANTI-SKID VALVE TO THE SWIVEL FITTING AS SHOWN ... . IF THE ASSEMBLY OF THE SWIVEL AND THE HYDRAULIC LINES ARE ROTATED 180 DEGREES, THE HYDRAULIC LINES CAN BE CONNECTED BUT THE SWIVEL WILL NOT OPERATE. THIS CAN CAUSE THE HYDRAULIC LINES TO BREAK DURING EXTENSION AND RETRACTION AND CAUSE THE BRAKES PRESSURE TO BE LOST." Examination of the swivel valves after the incident revealed that both valves were not installed as depicted in the maintenance manual.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

The improper installation of the swivel valve fittings by the operator's mechanic leading to the total loss of both hydraulic systems. Contributing to the incident were the swivel valves leaking and the total failure of the hydraulic system.

Full narrative available

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