NTSB Recommends Partial Redesign For Boeing 737 Engines

Boeing has been asked to overhaul the design and retrofit thousands of Boeing 737 next-generation aircraft after a flaw was discovered that resulted in engine fan blades escaping the engine when broken.

Southwest Airlines Boeing 737
Boeing will have to fix thousands of Boeing 737NG aircraft. Photo: Southwest Airlines

What are the details?

According to a finding by the American National Transportation Safety Board (NTSB), the Boeing 737 next-generation (NG) aircraft has a problematic flaw with their engine casing. Essentially, when the fan blade breaks due to a contained engine failure (such as when the aircraft engine ingests an object) it can break off a chunk of the casing itself, hitting the site of the main pressurized compartment and place the passengers on board at risk.

This exact scenario happened to a Boeing 737 Southwest aircraft and killed a passenger.


According to CNN, this flaw only affects Boeing 737 NG aircraft, typically the very popular Boeing 737-800. There are around 7,000 of this type flying in the world today. Boeing will need to ensure that all 7,000 have this fix.


The problem with the 737NG is unrelated to the Boeing 737 MAX groundings however it is the same aircraft that is affected by pickle fork cracks.

There are roughly 7,000 Boeing 737 NG aircraft that need to be inspected. Photo: David Peacock via Wikimedia Commons 

What has been Boeing’s reaction to this finding?

Boeing has come out of the gate praising the efforts of the NTSB.


“Safety and quality are Boeing’s top priorities and Boeing is committed to working closely with the FAA, engine manufacturers, and industry stakeholders to implement enhancements that address the NTSB’s safety recommendations.” Boeing issued in a press release. “We commend the NTSB for its thorough investigation into this accident. Our common goal is to help prevent similar events from happening in the future.”

And that they are deeply sorry for the events that transpired on that fateful Southwest flight.

“Our thoughts remain with the family and friends of Jennifer Riordan, who died from her injuries, with those who were hurt, and with all of those onboard. We are committed to doing our part in making sure an event like this never happens again.”

A Boeing 737-800
The Boeing 737-800 is the best-selling variant of the Boeing 737. Photo: Aero Icarus via Flickr

What will Boeing do to fix this issue?

Boeing has outlined several steps that they will take to tackle this issue.

First, they will be working with the engine manufactures to ensure that each of these engines on all of the aircraft are inspected as quickly as possible.

Additionally, engines that may be affected will be redesigned (and enhanced) to prevent the engine fan blade from being able to break out of the inlet and the fan cowl.

Boeing has said that no aircraft will need to be grounded nor any of the general public to be worried. This is a very rare occurrence and this minor tweak will settle the issue for good.

“All 737 NGs are safe to continue operating normally as the issue is completely mitigated by the fan blade inspections. In addition, Boeing is working on the design enhancements to fully address the safety recommendation from the NTSB. Once approved by the FAA, that design change will be implemented in the existing NG fleet over the longer term. This issue is limited to the 737 NG and does not affect the 737 MAX.”

The enhancement needs to go before the FAA in the USA before being rolled out.

What do you think? Is Boeing handling this situation correctly? Let us know in the comments.


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So, in addition to rampant pickle fork cracks, we now learn that the engine nacelle on the 737 NG has a sub-standard design. What’s next?

I note that, in the event of the recent uncontained engine failures of the A380 above Greenland and the A220 above Italy, puncture of the fuselage by engine parts did NOT occur.


To be fair, the much-reported Quantas A380 incident with an uncontained engine failure did puncture parts of the aircraft, resulting in reduced flight control and a fuel leak, as well as a partial loss of engine throttle control. It was sheer luck that the passenger shell was undamaged on that occasion.


It punctured parts of the wing…not the fuselage


Some more info in the link below. The failure of the engine fan casing is specifically associated with the “flattened bottom” shape of the engine, which was necessary to ensure adequate ground clearance on the 737NG (which has larger engines than on the preceding 737 Classic). So, yet again: a fatality caused by trying to squeeze extended service life out of an old 1960s design… https://www.flightglobal.com/news/articles/boeing-commits-to-ntsbs-recommended-cfm56-fan-cowl-462417/ In particular: “Murphy says the radial restraint fitting’s purpose was to help flatten the bottom of the CFM56 turbofan. The flat-bottom design allowed Boeing to address ground clearance issues that arose when it re-engined… Read more »


Interesting how the classic 737s (300,400,500) flat nacelles were even more pronounced don’t remember any failures with even a flatter bottom. The failure of the dovetail at the hub is in question. When was the last fan blade inspection? Who performed it? What process was used?


Is the cowling of CFM56 powered A320 ceo vulnerable in a similar way? I suspect not,.


Apparently not: the problem is specifically associated with the flattened bottom of the cowling on the 737 NG


Boeing has been alluding to a B737 replacement airframe for at least 10 years, possibly more.?
A new aircraft was promised & instead they just redesigned the wing attachment.!

TBH, I’m just waiting for them to go cap in hand to Airbus, asking them to take over their civil aircraft division, the way Bombardier had to.?


Over 10,000 airframes built and operating world wide since 1966. I’m sure Boeing would’ve loved to replace the 737 BUT the operators who fly and maintain the aircraft want continuity and familiarity for crews and mechanics. The push for the MAX included a lot of factors one of the biggest was the influence from the operators to maintain familiarity of the type.


Day after day, we are informed of security compromises in name of money making. Of course, Boeing is a major and proven actor in airplane conception and production, but the role of certification authorities is to disable commercial companies to act beyond security standards. Such modifications of the cowling should have been verified to keep the same level of confidence of previous cowlings . And don’t tell that operators dictate design of 737 NG. Once more, business dictate security compromises as for 737 Max. USA should be aware of such risks when leaving FAA without enough budget for independent security… Read more »

Norman clark

So, another problem…..I’m going to avoid all boeing…..they’re disastrou…


Boing earns billions and has friends in high places, it will just shrug off fatal crashes, groundings, bad press, cowling problems, fork cracks, lawsuits, structural failures, engine problems, tanker problems, battery problems…

S Walker

From an engineering point of view. The airline industry is in trouble. Very serious trouble. There is a divergence. Demand for economical to operate aircraft has never been at this level. At the same time cost cutting in getting the aircraft built and delivered is also at the highest it has ever been since WWII. But the mass production of WWII aircraft had only a small fraction of the complexity of aircraft built today. So the question comes up, can safe reliable aircraft that meet today’s demand be built without compromises or leaks in the safety bucket? It is possible,… Read more »