Boeing 737-2H4 N733TW

Summary

On 8 January 2008 at about 23:45 local time, a Boeing 737-2H4 registered N733TW, operated by Ameristar Air Cargo, Inc., was involved in an incident near Lincoln, Nebraska, United States. 38 people were on board and nobody was injured. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

8 January 2008 at 23:45

Classification

Incident

Location

Lincoln, Nebraska, United States

Nearest airport

Lincoln Muni (LNK)

Coordinates

40.8514, -96.7653

Aircraft

Boeing 737-2H4

Registration

N733TW

Category

Airplane

Engines

2

Operator

Ameristar Air Cargo, Inc.

Operating rule

Part 121: Air Carrier

Phase of flight

Not recorded

Route

Austin → Lincoln

Aircraft damage

Not recorded

Weather

VMC

Light

Night

NTSB number

CHI08IA065

Nobody was injured.

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.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

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.

Quoted verbatim from the NTSB record.