(dramatic instrumental music)
- [Narrator] This is the engine of a Boeing 777
that failed on February 20th, 2021.
- [Pilot] United 328 heavy mayday, mayday aircraft.
- It was flying from Denver to Honolulu
with 241 people on board.
Parts of it rained down
on a residential neighborhood near the airport.
Pilots were able to land the plane safely.
- [Passenger] Yay! (passengers cheering)
- [Narrator] And no one was injured.
But it wasn't the first time this happened.
The same type of engine, the Pratt & Whitney PW4000-112,
also failed on a Japan Airlines flight in December 2020
and another failed on a United Airlines flight
in February 2018.
In each case, regulators found that the engine fan blades
fractured due to fatigue or cracks.
In the 2018 incident,
the National Transportation Safety Board, or NTSB,
found that flawed inspections
by the engine maker Pratt & Whitney were the root cause.
The agency is still investigating all possible causes
of the most recent failures.
- [Controller] Denver-departure of United-
- [Narrator] Including Pratt & Whitney's inspection process.
(dramatic instrumental music)
The 1990s brought a lot of changes to commercial aviation.
New planes, like the Boeing 777 were introduced,
along with new engines to power them,
like the Pratt & Whitney PW4000.
Modern engines like the PW4000
feature lighter and more aerodynamic blades.
Instead of a solid piece of metal,
some fan blades have a hollow honeycomb interior.
But this style of fan blade
required new methods of inspecting them for wear and tear.
In 2005, Pratt & Whitney developed a new inspection method
using an existing technology
called thermal acoustic imaging.
The fan blades are hit with sound waves
that cause the structure to subtly vibrate.
If there's a crack somewhere
in the interior of the fan blade,
the vibration will cause friction and therefore heat
which an inspector's instruments
can detect on the fan blade's surface.
- [Announcer] The PW4000 has a state of the art design.
The result of more than 10 years of research
and hundreds of tests.
- [Narrator] In the 1990s,
the aerospace industry took a more active role
in setting training and certification requirements
for aircraft inspections.
The FAA maintained oversight,
but the industry had more input in developing standards.
The aerospace industry maintains standards
for a list of established inspection methods.
Inspectors are required to go through
hundreds of hours of training
to obtain certifications to use these methods.
But when an aerospace company, like Pratt & Whitney,
introduces a new inspection technique,
like thermal acoustic imagining,
it's classified as an emerging technology.
This classification allows manufacturers,
like Pratt & Whitney, to start using a new inspection method
without first developing a training program.
With oversight from the FAA,
the manufacturer is supposed to formalize
the inspection method over time.
But the NTSB found that because thermal acoustic imagining
was still classified as an emerging technology,
Pratt & Whitney never developed a formal training program,
even thought they'd used it to inspect
more than 9,000 fan blades over the course of 13 years.
Pratt & Whitney declined to comment,
citing ongoing investigations.
But the company previously said
that it would work with regulators on new inspections.
An FAA spokesman said the issue with the 2018 failure
was with the interpretation of the inspection result,
not the execution and that Pratt & Whitney
has since corrected the errors.
When the engine that failed in 2018 was last inspected,
the P&W employees that inspected it
did not attend one of the training sessions
on how to use the technology.
This was only possible
because it was classified as an emerging technology.
After the NTSB's report on the 2018 engine failure,
Pratt & Whitney agreed to formalize training
for thermal acoustic imagining.
The Pratt & Whitney engine that failed in February 2021
was last inspected in 2016,
before the new training standards,
raising questions about its accuracy.
Pratt & Whitney reexamined the records from that inspection
and refined how it interpreted the results
after the 2018 failure.
The reexaminations did not find any cracks in the blades,
according to the FAA.
Still, the inspection process
remains one of the focal points
in the NTSB's investigation into the 2021 failure.
- [Pilot] The United 238 heavy mayday aircraft
just experienced an engine failure.
Need to turn immediately.
- [Narrator] In this video
taken by a passenger on the February flight,
you can see the broken fan blade.
- Regarding the fan blade that was fractured at the root,
a preliminary on-scene exam
indicates damage consistent with metal fatigue.
- [Narrator] An NTSB spokesman said
their investigation of maintenance and inspection records
related to the most recent incident is ongoing
and that it's too early to draw conclusions about the cause.
Boeing said it was working with regulators
and that it supports the FAA's guidance
on inspection requirements.
- [Woman] It's so weird.
There's, like, smoke coming out
of one of the engines on that plane.
- [Narrator] The FAA ordered new inspections
that must be completed before planes
with this type of Pratt & Whitney engine
can be returned to service,
citing the likelihood of further fan blade failures.
(tense music)