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http://avherald.com/h?article=41254f9f&opt=0
Report: United A320 at Chicago on Oct 9th 2007, brakes wiring reversed
By Simon Hradecky, created Friday, Dec 26th 2008 12:05Z, last updated Friday, Dec 26th 2008 12:05Z

A United Airlines Airbus A320-200, registration N431UA from Seattle,WA to Chicago O'Hare,IL (USA) with 122 passengers and 5 crew, veered off runway 22R to the right, impacted runway lights, before returning onto the center line of the runway and subsequently taxiing to the gate. No injuries occured, however one flight attendant and a passenger went to hospital for examination, but subsequently released themselves. The airplane sustained damage to the engine nacelles and the left inboard tyre was blown.

The NTSB released their final report concluding, that the probable cause was

"The misrouted and reversed antiskid wiring by vendor maintenance personnel leading to the runway excursion. Contributing to the incident were the runway sign, the vendor's maintenance personnel not understanding the entire maintenance procedures in the dual tachometer replacement, and the operator's maintenance procedures being unclear to the maintenance personnel."

The captain was flying the airplane. The flight was uneventful until landing. Autobrakes were set to low. The airplane touched adown in the touch down zone a bit harder than anticipated. Reverset thrust was activated, but there appeared to be no autobraking. After the speed came below 100 knots, the captain applied manual brakes. The airplane immediately swerved hard right. Left full rudder and full left brake were applied to correct, but to no avail. The captain then used the nose wheel steering. At that time the airplane left the right side of the runway parallel to the runway impacting at least one runway sign, then began to track back to the left. The aircraft stopped on the runway. The captain knew there was some damage, but no fire, so he decided to taxi clear of the runway and to the gate. At the gate there was no temperature rise of the left brakes (indicating about 60 degrees Centigrade), while the right hand brakes showed overheating at 375 degrees Centigrade.

The first officer reported, that the right main and nose gear had departed the runway. Once stopped the captain informed the tower of the runway excursion, who in turn commanded the next airplane on approach to go around. The left brake temperature remained low as if the brakes had never been applied.

The wiring harnesses for number 1 and number 2 tachometers were mislabelled. The tachometers showed no anomaly.

Maintenance history showed, that the airplane had been in service between September 18th and 23rd for "Left Hand Main Landing Gear Sliding Tube Replacement". It was the last time during that maintenance, that the anti skid connectors for the #1 and #2 tachometers were disturbed. According to the maintenance manual a functional test - in order to identify cross wiring - was to be performed if more than one tachometer was replaced or disconnected.

The maintenance facility reported, that the Built In Test Equipment (BITE) would verify the wiring harnesses connections. The BITE test however did not verify the connection position.

United Airlines followed up with a letter (Dec 10th 2007) stating, that instructions regarding the functional tests were unclear. Only the incident airplane as well as one other airplane were found to be erroneously assembled in an extraordinary inspection of the tachometer assemblies on 45 aircraft. The documentation was revised by United Airlines.

However, on February 25th 2008 another United Airlines Airbus A320, registration N442UA departed the right side of the runway at Jackson Hole Aiport following a cross wiring of the left inboard and outboard tachometers (see also Incident: United A320 at Jackson Hole on Feb 25th 2008, slid off runway on landing).

The full NTSB report can be found via: http://www.ntsb.gov/ntsb/brief.asp?ev_id=2...023X01635&key=1

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