Updated: 3 days ago
Graphic picture and video's have been circulating on the internet of an incident with a Boeing 777-200 which showed a partially disintegrated engine #2 nacelle and the engine on fire.
This obviously generated massive media coverage and an abundance of public opinion.
Early investigation points to a fan blade failure of the engine and cascading effects of excessive vibration, as a result of which nacelle parts were shed and landed in a populated area near the departure airport of Denver. By sheer luck, nobody was hurt.
In addition, the engine caught fire in flight, which fortunately had no detrimental effect on the safety of the structure of the aircraft. As a consequence of the excessive vibration of the damaged engine, there was likely much more damage inflicted on the powerplant itself and the pylon structur, but further investigation will reveal the details.
Thanks to a capable crew and fortunate circumstances, the aircraft landed safely back at Denver with no injuries reported both on the ground and in the aircraft.
This article attempts to produce some more in depth documentary information about the background of the incident and its airworthiness aspects:
The B777 type aircraft has been certified and produced with different engine configurations with engines from different suppliers (Pratt $ Whitney, General Electric, and Rolls Royce). The event aircraft was equipped with Pratt & Whitney 4077 type engines.
See below the type certificate for more info.
Couple of factual remarks:
The Boeing 777 has an impeccable safety record and is one of the safest, if not THE safest commercial airliner design ever built.
Powerplants are complex subassemblies and type certificated in their own right.
This means that product development, design and production are managed and the ultimate responsibility of the Type Certificate holder, in this case Pratt and Whitney.
As a Type Certificate holder, Boeing carries for the safety of the complete type design and as such is a heavy stakeholder in engine type design.
The UK Civil Aviation Authority has issued a Safety and Operational Directive that prohibits the operation of Boeing 777 aircraft equipped with Pratt & Whitney 4077 engines into UK Airspace. See below
Another United Boeing 777-200 series aircraft on Februari 13, 2018 suffered a fan blade failure on the exact same engine type that was installed on a sister ship of the most recent event aircraft.
This failure was well documented and has striking similarities with the most recent event that occurred on 20-Feb-2021.
The fractured blade (in 2018) had been overhauled twice before it fractured, and had been subject to a Thermal Acoustic Imaging (TAI) inspection twice; in 2010 and in 2015.
It had accumulated 76704 flight hours and 14129 flight cycles when it failed.
Investigation of the inspection records after the event showed that there were minor indications with both TAI inspections on that particular blade but were misclassified as "paint".
Note that non visual non-destructive inspections often show indications that are caused by other factors than material deficiencies. It often takes experience to correctly classify indications.
After the February 2018 event, FAA mandated Thermo Acoustical Imaging Inspections on the fan blades by AD 2019-03-01. Downloadable below
On 24-Feb-2021 FAA issued an Emergency AD 2021-05-51 (downloadable below) pertinent to Pratt & Whitney 407x and 408x and 409x series engines.
This AD stipulates to, before further flight, inspect "certain" fan blades as per Thermal Acoustic Inspection (TAI) method as stipulated in Pratt & Whitney SB PW4G-112-A72-268 .
Implications will be that every individual fan blade's history needs to be retrieved and is applicable by SB, needs to be removed from the engine, shipped to an approved inspection facility and tested. After successful pass, it can be reinstalled and a complete engine can be returned to service. The AD notes that it is an interim measure, so additional rule making can be expected. Most likely after the NTSB (National Transportation Safety Board) have completed the investigation.
Compliance with the Emergency AD does not imply that the type can be operated into UK and Japanese airspace as there is a Safety Directive valid that effectively bans operation of the type.
Please note that the Emergency AD does not supersede the required actions as per AD 2019-03-01 which stipulates an initial TAI inspection on blades before accumulating 7000 engine cycles or before 6500 cycles at a flange split, whichever occurs first.
Subsequently, these inspections need to be carried out at 6500 cycles interval or 1000 cycles at flange split.
Any blade that fails inspection is to be discarded.
Below some of the NTSB investigation documents related to the February 13, 2018 event.
The captain written statement:
NTSB Powerplants group chairmans factual report:
NTSB Materials laboratory factual report:
Pratt and Whitney metallurgic final report:
Boeing Root Cause analysis
To be updated...