NTSB Factual Report

HISTORY OF FLIGHT

On June 10, 2005, at 1125 central standard time, a British Aerospace Avro 146-RJ85A transport category airplane, N530XJ, operated by Mesaba Airlines d/b/a Northwest Airlink flight 3437, sustained minor damage after a hydraulic line ruptured during landing roll-out on runway 17L at the Will Rogers World Airport (OKC), near Oklahoma City, Oklahoma. The airline transport rated captain, the commercial rated first officer, two flight attendants and 54 of the 56 passengers were uninjured. Two passengers sustained minor injuries. An instrument flight rules flight plan was filed for the scheduled revenue flight that originated from the Memphis International Airport (MEM), near Memphis, Tennessee, about 1015. Visual meteorological conditions prevailed for the flight conducted under 14 Code of Federal Regulations Part 121.

In a written statement, the captain stated that he heard a "pop noise and a sound of pressure releasing" during the final portion of the landing roll-out and just prior to turning onto the taxiway. He noted that hydraulic quantity and pressure on the "green side" was falling rapidly and the associated caution lights had illuminated. The pilot said the forward flight attendant called him and reported fluid spraying in the cabin and that some of the passengers were having difficulty breathing. The captain subsequently ordered a full evacuation of the airplane.

According to the first officer, he had just transferred control of the airplane to the captain in preparation to the turn onto the taxiway, when he heard a "bang". He contacted ground control and informed them that they were going to hold on the taxiway to identify the source of a noise. The first officer said the HYD MWS annunciator had illuminated, and both pressure and quantity were "falling." During this time, the captain said that he was losing nose wheel steering and stopped the airplane on the taxiway. A flight attendant notified the captain that there were strong fumes in the cabin and the condition was critical. The first officer said that he could hear children screaming in the cabin and that he started to smell fumes in the cockpit. After the captain ordered an evacuation, he contacted ground control to report that they were evacuating and needed emergency assistance.

According to a flight attendant, who was sitting in the aft jump seat, when the airplane was turning onto the taxiway she heard a "loud hissing" sound. She looked back and saw liquid "pouring out of the overhead around rows 5 and 6." The flight attendant called the captain and reported that there was liquid, fumes, and fog in the cabin and passengers were having a hard time breathing. She said the airplane needed to be evacuated, and the captain concurred.

According to the second flight attendant, when the airplane was turning onto the taxiway she heard a loud "pop noise" followed by a "hiss and a lot of fluid." The cabin looked "smoky" and the fumes were "strong." The three children seated in row 3 were "soaked", and were crying and rubbing their eyes. In addition, the passengers in rows 3, 4, and 5 also had fluid on them.

A Federal Aviation Administration (FAA) inspector performed an on-scene examination of the airplane. According to the inspector, the interior of the cabin around rows 2, 3, and 4 on the right side of the airplane was contaminated with hydraulic fluid (Skydrol), with the highest concentration located at row 3. There was also a puddle of hydraulic fluid on the ground just forward of the right wing. A portion of the airplane was disassembled to expose the three, 10-foot-long hydraulic lines that ran vertically along the circumference of the fuselage just forward of the right wing. The center, high-pressure hydraulic line (Pipe Assembly to Wing Services, Part number: HC279B0004-000) exhibited an approximate 3/8-inch-long crack at a shallow bend in the line. This bend was designed into the line during the manufacturing process.

At the time of the incident, the airplane had accrued a total aircraft time of 11,432.41 hours and a total of 11,095 cycles.

The operator reported that on September 1, 2004, another like airplane in their fleet was taxing to the runway for departure when the same-type hydraulic line ruptured between rows 13 and 15 and subsequently filled the cabin with fumes and fluid. The flight crew, two flight attendants, and 41 passengers evacuated the airplane on a taxiway. There were no injuries during that event. The failed line from that previous event was shipped to the manufacturer for examination. Their examination revealed that the line failed at a bend due to a longitudinal defect on the inner diameter. The report concluded that the longitudinal defect occurred during the manufacturing process, and inspection specifications revealed that the line should have been rejected prior to entering service.

The failed hydraulic line from this incident was examined at the Safety Board's Materials Laboratory in Washington, D.C. The examination revealed that the hydraulic line also failed at a bend due to a fatigue crack on the inner diameter near a longitudinal defect that measured .0012-inches in depth. This defect was also noted on three other areas of the line and extended along the entire inner diameter surface at the base of a weld. Examination of the fracture features indicated the longitudinal defect occurred during the manufacturing process.

According to the manufacturer's inspection specifications, any line that had a defect measuring over .002-inches was rejected. If the defect measured below that standard, then the line was considered acceptable provided that the defect could be removed and the line continued to meet wall thickness and ovality requirements. As a result of this investigation, the Safety Board made several suggestions to the manufacturer in order to avoid and detect cracking, as well as identifying the ones in the field.

NTSB Probable Cause

Failure of a high pressure hydraulic line from fatigue as a result of a manufacturing defect.