Airbus A320 N442UA

Summary

On 26 February 2008 at about 04:16 local time, a Airbus A320 registered N442UA, operated by United Air Lines, was involved in an incident near Jackson, Wyoming, United States. 125 people were on board and one had minor injuries. The aircraft was slightly damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

26 February 2008 at 04:16

Classification

Incident

Location

Jackson, Wyoming, United States

Nearest airport

Jackson Hole (JAC)

Coordinates

43.6061, -110.7386

Aircraft

Airbus A320

Registration

N442UA

Category

Airplane

Operator

United Air Lines

Operating rule

Part 121: Air Carrier

Phase of flight

Not recorded

Route

Denver → Jackson

Aircraft damage

Minor

Weather

VMC

Light

Night

NTSB number

DCA08IA044

1 person had minor injuries.

the loss of braking action on the left main landing gear due to the cross connection of the wheel speed tachometer wires that was caused by inadequate maintenance performed on the airplane during the installation of the main landing gear.

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

Read the full NTSB narrative

The flight crew reported that prior to the approach into KJAX, the captain performed an approach briefing which included that the Mu readings indicated "good" breaking; it was determined that if the airplane did not touchdown in the first 2,000 feet of runway, they would perform a go around.  The touchdown was "firm" and the captain believed it was within the first 2,000 feet of runway.  The deceleration was normal until the airplane reached about 80 knots when it started to slide.  The captain then applied maximum manual braking and the airplane started to slide toward the right side of the runway.  The airplane exited the end of the runway and came to rest in the snow.  The runway friction measurements taken before and after the incident were all above 0.45, which according to the Aeronautical Information Manual, is above the level when braking action would start to deteriorate. Therefore, the airplane braking performance was not deteriorated by the runway conditions. There were no faults logged in the maintenance systems that were relevant to the antiskid or brake systems, however, the inboard (IB) and outboard (OB) tachometer wires on the left main landing gear (LMLG) were found to be cross connected. With the wires crossed connected, when the IB tire began to skid (stop rotating) the Brake Steering and Control Unit (BSCU) would have commanded a reduction in the hydraulic pressure to the OB brake, instead of the IB brake, causing a loss of braking on the OB wheel. At the same time, the BSCU would have continued to command an increase in hydraulic pressure to the IB brake, causing it to fully skid and fail. Therefore, when the captain applied full manual braking, the braking action on the LMLG was almost fully lost while the right MLG braking remained normal, resulting in the airplane veering to the right and exiting the runway. A review of the maintenance documents and practices showed that there were no specific inspections required when the landing gear and wiring harnesses were received to ensure they were routed to the correct axle. Additionally, installation documents did not specify the exact wire number connector that needed to be installed on each tachometer for a given position. Finally, a proper functional check should have identified the cross connected tachometers, even though maintenance personnel indicated no discrepancies when tested. After the incident, United Airlines took numerous actions to prevent similar incidents from reoccurring.

Quoted verbatim from the NTSB record.