"A Northwest Airlines pilot's decision to shut down an engine, combined with a hydraulic problem, caused the May 2005 ground collision of two Northwest jets at the Minneapolis-St. Paul International Airport, federal investigators have concluded.
The Boeing DC-9 pilot's action just after landing in the Twin Cities meant that the plane lost all power to its steering, brakes and thrust reversers, causing it to strike an Airbus A319 that was being pushed back from a gate, according to a report issued last week by the National Transportation Safety Board.
The report detailed the events leading up to the accident and the investigation.
The DC-9, with 94 passengers on board, experienced problems with its right-side hydraulic system that powers its steering and brakes soon after leaving Columbus, Ohio. The captain decided to continue flying and declared an emergency as the plane neared the Twin Cities' airport.
After landing, the captain shut down the left engine, which powered the only fully functioning hydraulic system. As a result, the flight crew couldn't steer the plane or use the brakes and thrust reversers. The DC-9 hit a wing of the A319, with 38 passengers aboard, damaging the DC-9's cockpit and spilling fuel. Both planes were evacuated. The DC-9 pilot was seriously injured and seven passengers and crewmembers from both planes had minor injuries.
The NTSB report cited a "fatigue fracture" of the DC-9's rudder shutoff valve, which caused the loss of right-side hydraulic pressure, as a contributing factor in the accident.
Since the accident, Northwest developed an inspection procedure for its fleet in which "any rudder shutoff valve found to have a crack indication was replaced prior to further flight," said company spokesman Roman Blahoski. He declined to comment on the NTSB report.
A spokesman for Air Line Pilots Association at Northwest said the union could not comment on the report.
The NTSB report noted that Northwest recorded 38 instances of DC-9 rudder shutoff-valve housing failures from May 2000 to April 2005. "Northwest reported that they were aware of the cracked valve housings of the rudder shutoff valve prior to the accident" and after a 2003 analysis, according to the report. "The failure of the valve by itself was not determined to be a safety of flight issue and was therefore deemed solely a reliability issue."
After the accident, Boeing issued a "service letter" regarding the replacement of rudder shutoff valves."
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