The 777 has been flying for 25 years with almost no fatal accidents. Unless your flight will be flying over Russian anti-aircraft missile batteries or through a wormhole above Malaysia, you should be perfectly safe.
Another way of looking at it is that after flying and accumulating 25 years of wear and tear without major incident, we now have seen a repeatable flaw that these aircraft may encounter due to their age.
Aircraft undergo regular preventative maintenance checks, with letter codes A - D. The D check being the most comprehensive, it occurs every 6-10 years and basically the entire aircraft is taken apart and inspected, looking for among other things anything like stress fractures, corrosion, unusual wear, etc.
A commercial aircraft does not just accumulate wear and tear for 25 years until something breaks. They can basically fly indefinitely, but in reality after two or three D checks they are usually retired because the cost of the D check is more than the value of the aircraft.
Great context. I gained a lot of respect for aviation's use of checklists and procedures from the book 'The Checklist Manifesto'
In this case, something obviously went awry and it's both engineering, planning, and a miracle no one died or was crushed from debris from above. Regardless, comments like yours leave me feeling far more confident in this sort of thing.
> In this case, something obviously went awry and it's both engineering, planning, and a miracle no one died or was crushed from debris from above. [...]
Yes, though even something going wrong doesn't necessarily mean that we'd need to change any procedures.
Sensible procedures bring risks down to acceptable levels at an acceptable price. That level of risk is generally still more than 0%.
Beware of the dangers of preventative maintenance, where sometimes while replacing or inspecting or re-mounting inspected parts, the maintenance crew breaks something that was OK and probably going to be working fine for years.
But yeah, a D check is so expensive I've heard there's a habit of dumping the aircraft on less observing flying companies some thousand miles before it comes up...
And in a similar incident in February 2018 on a 777 (referred to upthread), one of those checks was found to have failed: the NTSB determined that the root cause was a cracked engine fan blade that should have been detected on a previous inspection (and that would have resulted in the blade being replaced), but wasn't. If this incident turns out to have a similar root cause, that means there are issues with the preventive inspection and maintenance process.
It's not taken totally apart, but it is stripped of the interior down to the bare metal, all wiring is checked/replaced as needed. All mechanical parts like the flaps and landing gear are removed and checked for wear. The skin is checked for cracks. This is done every 5 years for planes, taking about 5-6 weeks to complete.
As well as two demonstrations that the aircraft meets the design specification that even a catastrophic failure in the worst stage of flight is easily recoverable. I'd expect an increased inspection rate, possibly some new mandated ND testing for fractures and discontinuities (the last one was an LP shaft failure, IIRC).
One thing that does bug me, though is that we now have two events where the shroud was lost. Were these uncontained failures (problematic because of potential for wing damage) or contained faiLures followed by aerodynamic shedding of the damaged shroud (system functioning as designed). I'm also somewhat concerned about the fire remaining in the burner stage. Might have just been lubricants, but I'd want to make sure the fire handle had been pulled and investigate whether it worked correctly.
It looks it’s the “cowling” that was lost, not the protective shroud / containment around the fan (and the rest of the engine) that keeps the fan/compressor/turbine blades from becoming high speed radial projectiles when they break off at full speed.
Agreed. The last one was pretty clearly a failure of a shaft or turbine, and the damage was much more obvious. This might be something completely different.
> As well as two demonstrations that the aircraft meets the design specification that even a catastrophic failure in the worst stage of flight is easily recoverable.
But in that type of failure, you can't control where the pieces go.
Kinda.
While the 2018 incident was "contained", it still resulted in damage to the fuselage.
"Two small punctures were found in the right side fuselage just below the window belt with material transfer consistent with impact from pieces of an engine fan blade"
Not 'kinda'. Debris exiting the engine housing with sufficient energy and in a direction that leads to damage of other systems is the literal definition of an unconfined engine failure (i.e. it can spit as many parts as it wants to out the exhaust). There is a band of armour around the plane of the fans that should prevent any blades leaving the engine perpendicularly. If there was fuselage or wing damage from debris, that was an unconfined failure and would require investigation as a major fault.
However, loss of the shroud doesn't necessarily imply there was a confinement failure. Damage to the shroud during the event can easily lead to the cowling shedding aerodynamically, which is also part of the design: the last thing you need is more drag on the dead engine side. We can't tell which that was in this case, but it's important that we do---the design criteria specifying that the aircraft can be safely recovered from a catastrophic single engine failure during any stage of flight would assume the failure is confined to the engine.
Engine age isn’t the same as airframe age, and components don’t age linearly with calendar time; they age with flight hours or pressurization cycles. Without access to a log book, it’s impossible to know how old an engine is or when it was last overhauled.
Indeed, for a 25-year-old airframe with the utilization it would have at a major carrier like United there's basically no way the engines hanging on it now could be the same engines it was delivered with.
Unlike some codebases, aircrafts actually have mandated maintenance. Which is why most accidents are due to human error and not massive technical failures.
(That's a feature, not a bug! The pervasive checklists and general professionalism mean that most 'normal' human errors are recovered from without enough consequences to make it into the news.
So only the really unlucky and incompetent are what we usually hear about.)
Engines are separate from the airframe; on big commercial aircraft the engines get swapped/moved around all the time (the engines may well be on lease, separate to the lease on the airframe). Thus, in this sort of situation it's the engine's history that'll be important, rather than the airframes.
Until the NTSB investigates, there's no way to know whether age has anything to do with it. It might. It might not. There could be a common cause, or there isn't.
>> a repeatable flaw that these aircraft may encounter due to their age.
There are hundreds of flaws. Aircraft are not perfect. Any large airframe sees lots of little things break every year. That's what inspections and maintenance are for. But the system is designed so that such things never add up into something really bad. Be worried about the aircraft without flaws. To me, that means it either never gets used or isn't being inspected properly.
Or also if your pilots have just finished their type rating and used to fly A320s. Hopefully they remember that you actually need to manage your throttle on a Boeing!
