CHI08FA050

On approach for landing, about 13 miles from the airport, the flight crew was informed that the cabin was filling with smoke. The cabin crew was unable to determine the source of the smoke. The captain declared an emergency in order to get the airplane on the ground as soon as possible. The first officer performed a normal landing and turned off on the first high-speed taxiway, at which time he noticed a low oil indication on the right engine. The engine was subsequently shut down. The captain elected to initiate an emergency evacuation due to the uncertainty of the situation and the possibility of a fire on-board. During the evacuation, one passenger sustained a fracture of a vertebra. Post accident examinations revealed a low oil quantity in the right engine, with metallic deposits on one of the engine chip detectors. A detailed teardown inspection of the right engine revealed the #2 bearing had failed. The compressor gas path exhibited oil deposits consistent with oil migration into the airplane's environmental system. The cabin pressurization system utilized 8th and 15th stage engine compressor bleed air. No evidence of an engine or cabin fire was observed. The engine manufacturer had released an improved bearing design prior to the accident. At that time, the operator began replacing the bearings on an attrition basis when the original bearings were no longer serviceable. However, the operator has revised that policy and is proactively replacing the original bearings, regardless of the condition, with the improved bearings.

History of flight

On December 14, 2007, at 1555 central standard time, a Boeing 777-222, N220UA, operated by United Airlines as flight 836, sustained minor damage when smoke entered the cabin during approach for landing at O'Hare International Airport (ORD), Chicago, Illinois. The international air carrier flight was being conducted under 14 CFR Part 121 on an instrument flight rules flight plan. One passenger was seriously injured during the subsequent emergency evacuation. The remaining 248 passengers, 11 cabin crew members, and 4 flight crew members were not injured. The flight departed Pudong International Airport (PVG), Shanghai, China, about 0900 UTC. ORD was the intended destination.

The captain was advised that the business class lavatory sinks were overflowing about 4 hours into the flight. He decided to close the affected lavatories for the remainder of the flight. There were no further issues until the flight began a descent from cruise altitude in preparation for landing at ORD. At that time, one of the Relief First Officers reported that the lavatory immediately aft of the flight deck also had water problems.

The captain stated that while on approach for landing, about 13 miles from the runway threshold at 5,000 feet mean seal level (msl), he was informed that the cabin was filling with smoke. The flight attendant commented that she could not see the aft end of the airplane due to the density and that it was getting worse. The cabin crew was unable to determine the source of the smoke. The captain elected to declare an emergency and to get the airplane on the ground as soon as possible.

The captain reported that approximately 5 miles from the runway, the Instrument Landing System (ILS) localizer and glide slope display indicated that the data was unreliable. The Engine Indication and Crew Alerting System (EICAS) indicated that the autopilot was operating in a degraded mode. The flight crew thought that these indications may have been related to the previous lavatory water issues. The captain elected to continue the approach, noting that the presence of a high broken cloud layer would still give them sufficient time to transition to a visual approach and land safely. The first officer performed a normal landing and turned off on the first high-speed taxiway. As the captain took control of the airplane, the first officer noticed a low oil indication on the right engine. The engine was subsequently shut down.

Due to the indications of multiple problems with the airplane, the captain elected to initiate an emergency evacuation. During the evacuation, one passenger sustained a serious injury.

Personnel information

The captain held an Airline Transport Pilot certificate with single and multi-engine class ratings, and a Boeing 777 type rating. He was issued a First-Class Airman Medical certificate in September 2007. He had accumulated 4,327 hours in Boeing 777 airplanes at the time of the accident. His most recent flight check was completed in March 2007.

The first officer flying at the time of the accident held an Airline Transport Pilot certificate with single and multi-engine class ratings, and a Boeing 777 type rating. He was issued a First-Class Airman Medical certificate in July 2007. He had accumulated about 4,597 hours flight time in a Boeing 777. His most recent flight check was completed in July 2006.

Aircraft information

The accident airplane was a Boeing 777-222 airplane. The airframe had accumulated approximately 26,287 hours at the time of the accident. The most recent inspection under the operator's continuous airworthiness inspection program was completed on August 10, 2007.

The airplane was powered by two Pratt and Whitney PW-4090 turbo fan engines. Each engine was capable of developing 90,000 pounds of thrust. The left and right engines had accumulated 22,211 hours and 39,502 hours time in service, respectively.

Meteorological information

The Chicago O'Hare Airport Automated Surface Observing System (ASOS) recorded conditions at 1551 as: Broken clouds at 2,200 feet above ground level (agl), 10 miles visibility, winds variable at 4 knots, temperature -4 degrees Celsius, dew point -9 degree Celsius, and altimeter 30.40 inches of mercury.

Wreckage and impact information

The airplane landed normally on runway 10 (10,144 feet by 150 feet, asphalt/concrete) and exited on taxiway M5. The emergency evacuation was conducted on the taxiway.

A post accident inspection revealed that white smoke was being emitted from the right engine. Further on-scene investigation noted a low oil quantity in the right engine. Metallic deposits were observed on one of the engine chip detectors. In addition, oil deposits were located in the compressor section of the engine. No evidence of an engine or cabin fire was observed.

Water infiltration was observed in the electrical equipment compartment located below the flight deck. The infiltration was in the area of the ILS navigation receivers. Further examination revealed that the business class lavatory drainage system was obstructed at the drain masts, due to a failure of the drain mast heaters.

Survival aspects

An emergency evacuation was conducted on the taxiway after landing. All exit doors operated without any reported difficulties and all exit slides deployed properly.

One 68-year-old passenger, who exited on the right side of the airplane, sustained a compression fracture of a vertebra. The remaining passengers and crew were not injured.

Tests and research

A detailed teardown inspection of the right engine revealed the #2 bearing had failed. The compressor gas path exhibited oil deposits consistent with oil migration into the airplane's environmental system. The cabin pressurization system utilized 8th and 15th stage engine compressor bleed air.

The right engine had accumulated 39,502 hours and 5,814 cycles in service. The #2 bearing had been in service 34,440 hours since new and 10,315 hours since it was last overhauled. The magnetic chip detectors had been inspected and cleaned 240 hours/26 cycles prior to the accident.

The engine manufacturer had released an improved bearing design prior to the accident. At that time, the operator began replacing the bearings on an attrition basis when the original bearings were no longer serviceable. However, the operator has revised that policy and is proactively replacing the original bearings, regardless of the condition, with the improved bearings.