The Federal Aviation Administration (FAA) has stated through three proposed airworthiness directives that, subject to inspections and modifications, 777-200s equipped with Pratt & Whitney (PW) engines could be back in service in only a few months.
On February 20, United flight 328, operated by a 777-222 (line number 5 and built-in 1994, one of the first units of the model to enter service) on its way up from Denver to Honolulu, Hawaii, suffered a catastrophic failure of the number 2 engine just four minutes after takeoff. Although the event ended up leaving a two-kilometer debris field over the town of Broomfield, Colorado, there were no people injured on the ground; the plane landed safely twenty minutes later. Following this incident, and after analyzing several engine failures of almost identical characteristics on PW4000 series equipped aircraft, United – as well as several other world operators of this type – decided to ground the aircraft powered by these engines. A total of 124 aircraft were suspended from operation.
According to the NTSB’s preliminary report, the engine failure was caused by the detachment of a fan blade with compatible evidence of a material fatigue failure. While strictly speaking the fault was controlled – as no internal engine parts were ejected – the impact of the fan blade against the casing caused the aerodynamic cowling to detach and rupture oil and fuel lines, resulting in a fire at the rear of the engine. Three days after the incident, the FAA ordered an immediate inspection of 777s equipped with PW4000 engines.
As part of the return to service approval, the FAA mandated that engine cowlings be reinforced, blade inspection is improved, and «certain systems and components be inspected». The directives will require remediation based on the results of these inspections.
According to Reuters, United stated that the proposed directives «will be beneficial for the industry», adding that » the majority of the affected engines have already been subject to these inspections before the FAA ordered it». For this reason, United indicated that the aircraft should rejoin its fleet early next year. United is the only U.S. operator of 777s equipped with PW engines, with 52 aircraft of the type.
This was echoed by Boeing. The manufacturer recommended to the airlines -days after the February incident- to stop operating the model until determining the steps to be taken to ensure safety. Pratt & Whitney, for its part, indicated that the inspection of the blades, which must be carried out by means of thermo-acoustic visualization technology, «is already in progress».
