Recent Groundings of the Boeing 777 explained
This Saturday as United Boeing 777-200, on flight UA-328, was through initial climb when the aircraft right-hand engine (PW4077) inlet separated associated with an engine failure.
The crew with 229 passengers on board, declared mayday and returned for landing at Denver.
Following this incident, United Airlines grounded all of its active Boeing 777 aircraft powered by the Pratt and Witney 4000 engine while other airlines from Japan and South Korea grounded the same aircraft. UK has banned the aircraft with the same engine type being flown over their airspace.
According to Boeing, 69 777 jets are in service which are powered by the same engine, while 59 such aircraft are in storage.
What led to the grounding of these aircraft was the Emergency Airworthiness Directive (EAD) released by FAA which required immediate inspections of Boeing 777 aircraft with certain PW4000 engines.
"We reviewed all available safety data following yesterday's incident. Based on the initial information, we concluded that the inspection interval should be stepped up for the hollow fan blades that are unique to this model of the engine used solely on Boeing 777 airplanes." - FAA
An Airworthiness Directive (AD) is a notification to owners and operators of certified aircraft that a known safety deficiency with a particular model of aircraft, engine, avionics, or other system exists and must be corrected.
ADs are divided into two categories:
Those of an emergency nature requiring immediate compliance before further flight, and
Those of a less urgent nature requiring compliance within a specified period of time.
An aircraft that does not follow an issued Airworthiness Directive is not considered airworthy thus it's mandatory to comply with an AD.
ADs are issues mainly as a result of service difficulty reported by operators or from the results of aircraft accident/incident investigations.
They are issued either by the national civil aviation authority of the country of the aircraft manufacture.
The aircraft would remain grounded until inspections are complete and it is determined that the aircraft is safe to fly.