Safety event: February 13th 2018
*click images for source*
United Airlines flight 1175 service from San Francisco (SFO) to Honolulu (HNL) suffered an uncontained engine failure of the number 2 engine (Pratt & Whitney PW-4077) approximately 35 minutes prior to arrival at Honolulu International Airport. The flight was operated by Boeing 777-222 registration N773UA, which was the 4th 777 ever built and was the first ‘service ready’ airframe, which conducted the original 1,000 ETOPS certification test flights before delivery to United in January 1996.
The aircraft made an uneventful emergency landing on runway 8R, with ARFF (aircraft rescue fire fighting) equipment at the ready. The aircraft taxied to the gate where the passengers disembarked normally.
Based upon early images of the aircraft on the ground after the event, it appears that a fan blade of the number 2 engine (on the right wing) became detached, damaging a second blade and subsequently resulting in the loss of the engine inlet, cowl/nacelle and part of the kevlar reinforced fan casing. A passenger of the flight posted a video of the damaged engine and the vibration in flight to Twitter shortly after the landing.
The engine would have been shut down immediately to avoid further damage and risk to the aircraft, so the vibration seen in the video would come partially from the windmilling of the damaged fan disk, but mostly from the disruption of the airflow around the engine due to the missing section of the nacelle. The engine casing is designed specifically to guide the airflow around itself and onto the wing.
The heroes of the day here are the crew, who performed a flawless descent and landing under very testing conditions. If we look at the path of the approach and landing, we can see how the crew made a looping right turn onto finals. Due to the loss of power on the right hand side of the aircraft, it would have a natural tendency to turn to the right, as the left side is providing the power, while the damaged engine acts like a brake due to the drag it is generating. Therefore the right turn is far less stressing for the crew and aircraft. All twin-engined aircraft are designed to operate on a single engine for extended periods of time, including during take-off.The Boeing 777 features a system called TAC (thrust asymmetry compensation) which automatically uses the rudder to counteract the yaw generated by asymmetric thrust once the aircraft is over 70 knots, which reduces the work load of the crew.