Washington: Damage to a fan blade on an engine that failed on a United Airlines Boeing 777 flight is consistent with metal fatigue?

CPT Gurinder (Gene) Rana — Wed, 24 Feb 2021 08:20:52 -0500

What exactly is metal fatigue in the engine of a Boeing 777, especially post takeoff; doesn't engineering endure air worthiness of the plane before it is placed into service and; who is to blame?

Response by MSG Private RallyPoint Member made Feb 24 at 2021 8:47 AM

MSG Private RallyPoint Member — Wed, 24 Feb 2021 08:47:08 -0500

Everything has a breaking point, whether it be people or objects. Perhaps no one is to blame.

Response by SFC Melvin Brandenburg made Feb 24 at 2021 11:12 AM

SFC Melvin Brandenburg — Wed, 24 Feb 2021 11:12:43 -0500

sometimes things fail. Everything man made is going to fail eventually. But, nobody knows when eventually actually is.

Response by LTC Jason Mackay made Feb 24 at 2021 11:51 AM

LTC Jason Mackay — Wed, 24 Feb 2021 11:51:02 -0500

Could be a flaw in the titanium structure. Something mundane as a few degree temperature shift during the forging process (like a cold draft be opening a door). Could be a few thousands or tenths of an inch off tolerance during a very complicated 5 axis mill process (blades are curved in three dimensions and hollow. Titanium is challenging to machine and weld.)

Everything has a statistical mean time to failure, but statistically there are outliers. Always are

Response by SSG Bill McCoy made Feb 24 at 2021 2:57 PM

SSG Bill McCoy — Wed, 24 Feb 2021 14:57:56 -0500

I am NOT an expert, nor am I a metallurgist. After the Army, I was the head of security for the largest Specialty Steel producer of stainless, titanium and other alloys used in aerospace, military and automotive applications. I do know that when those metals were produced, stringent testing was done prior to whatever metals were delivered to our customers. Just from our product brochures, it was also obvious that, in addition to testing, our end products sold were with information about expected lifespan as related to "metal fatigue."

That said, the fatigue can be a product manufacturing issue, or an issue with using the final product beyond it's intended lifespan. While there is always a area of "between" point A and point B, the recommended parameters in aerospace are pretty stringent. When components go beyond their maximum (point B) lifespan, "fatigue" becomes a major issue.

Response by SFC Ralph E Kelley made Feb 24 at 2021 5:21 PM

SFC Ralph E Kelley — Wed, 24 Feb 2021 17:21:50 -0500

I blame COVID-19. ~sarmark~

Response by LtCol Robert Quinter made Feb 25 at 2021 6:06 AM

LtCol Robert Quinter — Thu, 25 Feb 2021 06:06:42 -0500

When an aircraft is designed, every part has an anticipated life dependent upon either the failure rate of similiar parts in similiar installations or the estimated life in the particular installation. The estimated life of a part is used to create the inspection or phased maintenance schedule of the particular model aircraft. Whenever a specific situation occurs where the stress on a part or system occurs, the "overstress" circumstance is reported and/or recorded and appropriate modifications to the inspection schedule are made. While every effort is made to anticipate problems, not all situations can be anticipated or failures predicted because of all the variables. In recognition of this, other systems are installed to indicate failing systems, but the fact is, failures will occur at unanticipated times and minimization of the damage falls on the ultimate safety system, the pilot. Even then, variables in training, retention of the training and unanticipated failures in the pilot system will occur (stroke, heart attack, et.) might occur to determine the outcome. Not everything can be predicted with so many variables.

Response by LTC Ken Connolly made Feb 25 at 2021 11:17 AM

LTC Ken Connolly — Thu, 25 Feb 2021 11:17:24 -0500

Over time heat and stress will weaken metal. Just like if you take a coat hanger and keep bending it back and forth. It will eventually break. There are tests that can be conducted on engine parts, but to do that the engine has to be disassembled.

Response by SGT Clarence Gilbert made Mar 9 at 2021 5:26 PM

SGT Clarence Gilbert — Tue, 09 Mar 2021 17:26:54 -0500

In the words of Forged in fire.... "you had a crack that could not be seen"