MD-11 Louisville accident Nov 4, 2025, versus Chicago DC-10 accident May 25, 1979
- bart
- Jan 16
- 5 min read
Updated: Jan 18
The tragic accident of the Louisville MD-11 on take off which killed the crew and 11persons on the ground reminds many people familiar with both MD-11 and DC-10 aircraft of the accident with a DC-10-10 at Chicago O'Hare on May 25 1979.
The DC-10 accident is referenced in the MD-11 preliminary report on page 11 (document at the bottom of this article).
There are certain commonalities between the two accidents, but the totality of circumstances and extent of investigation (so far) of both accidents are vastly different.
Here are the similarities;
Wing pylon structural architecture of MD-11 and DC-10 are the same.
Failed structural members on both accidents are te same (Wing pylon aft attach point between the wing and pylon aft bulkhead)
Flight phase of the failure are the same. Structural failure occurred during take off roll past V1.
Primary failure effect are the same. Engine at take off thrust rotated over the top of the wing.
That is where the similarities stop!
Below are the differences in secondary failure effects;
The separation of the engine on the DC-10 caused a loss in electrical busses, hydraulic system and, most importantly, caused the slats on the left hand wing to retract. This in turn caused the aircraft to stall asymetrically, roll through 90 degrees to an unrecoverable roll angle and subsequently crash. Details in the NTSB report at the bottom of this article.
On the MD-11, the separated engine rotated over the top of the wing, ignited streaming fuel and hit the centre engine, which surged and likely lost thrust, preventing the aircraft to climb above 30 ft.
The last page on the investigative update contains a graphic desplate of some DFDR parameters. Document posted at the bottom of this post.
Clearly the parameters on engine #2 went haywire, most likely due to the impact by the separated engine from the left hand wing.
Investigation Progress as of Jan 2026 on the MD-11 accident:
NTSB has located the failed parts in the MD-11 pylon and reported such in the preliminary report. The failed parts were the aft pylon bulkhead and the spherical bearing still attached to the wing clevis fitting.
The cause of the failed pylon aft mount; a split spherical bearing outer race was identified as the root cause of the structural failure that initiated the cascade of failures that caused the aircraft to crash.
The theory is that the cracked and split spherical bearing outer race initiated fatigue cracking in the pylon aft mount fitting which consist of a dual lug fail safe configuration..
So far, no other causal factors contributing to the occurance of the accident have been identified.
In order to better understand the cascade of events and contributing factors to the accidents, further analyses would be required. Photo of the failed part below.
A fully assembled aft pylon joint is shown below. One can observe that the pylon aft bulkhead lugs are mostly shielded from view by the wing clevis and only accessible from the sides. This makes a visual inspection virtually ineffective for detection of damage prior to failure.
Investigation elements of the DC-10 accident:
From the wreckage a selection of structural parts were retrieved and a sequence of events could be reconstructed by exhaustive investigation.
Subsequently the following studies were conducted post-accident;
Post accident fleet inspections revealed potentially catastrophic cracking in a number of previously in service aircraft.
Post accident static and dynamic stress tests were conducted on undamaged and damaged structure to determine practical damage tolerance (residual strength and crack growth rate)
Post accident flight tests have been conducted by McDonnell Douglas to confirm stresses on relevant structural parts in certain maneauvering conditions both airborne and on ground).
Simulator tests with multiple crews in order to determine the effectiveness of existing published flight techniques and survivabilities of the upset as experienced during the accident with particular attention on asymetrically retraced slats.
Investigation into effectiveness of published maintenance procedures and adherence to these procedures, including equipment mainteance and what is currently known as human factors.
After the DC-10 accident investigation had been completed, a number of 12 safety recommendations were issued by NTSB.
The current investigation on the MD-11 accident has not been finalised and has not yet progressed to the level of detail of that of the DC-10 accident at O'Hare.
Existing Airworthiness Management information on MD-11 pylons aft attachments
General Visual inspections and Detailed Visual inspections on the aft attachments are stipulated by the operators Approved Maintenance Program (AMP) at 72 months interval. These inspections were last carried out in 2021. So roughly two years to go until the next scheduled inspection would come due.
A lubrication task was stipulated in the operators AMP at a 24 months interval. Last carried out at 18-Oct-2025.
A Special detailed Inspection (SDI) was due at 28000 Flight Cycles and still had 6957 Flight Cyles to go, which realistically was a few years away.
After four reported spherical bearing outer race failures on three different aircraft, Boeing released Service Letter MD-11-SL-54-104-A, which suggests a periodic visual check of bearing outer race migration, which would supposedly detect a disintegrated outer race as found in the accident wreckage. This was likely the SDI metioned in the previous bullet.
The SL also stated that an improved spherical bearing was approved for installation without the recess where cracking initiated on the accident aircraft.
After the accident FAA issued an emergency Airworthiness Directive 2025-23-53 (supersedes 2025-23-51), stipulating Inspections and corrective actions are performed, using a method approved by the manager AIR-520, Operational Safety Branch FAA before further flight.
Tentative conclusions and open questions
An in flight engine separation is almost without exception catastrophic although different aircaft types have landed safely with a separated engine. Catastrophic factors may not be structural failures per se but system disruptions such as degradation by fire, hydraulic systems and uncommanded flight control movements or failures thereof.
The exact mechanism of a failed bearing race and subsequent development into the pylon aft mount lug failure needs to be better understood and reconstructed.
Clearly the phenomenon of a failed pylon aft mount spherical bearing failure was never perceived as a potential flight safety issue by the Type Certificate Holder (TCH) which is Boeing. If so, the prudent action would be to issue a Service Bulletin (SB) and not an SL. Why this was misjudged would be an issue to addressed in the final investigation.
Unclear is whether the FAA ever received reports of the failed aft pylon spherical bearing failures and wheather they questioned the TCH on this issue.
Both in the DC-10 as well as in the MD-11 accident, previous reports were known indicating structural damages that eventually led to these two fatal accidents. The reason why this never lead to adequate Airworthiness Management Actions is an extremely important question to answer.
In closing;
The contributing factors leading op to this accident indicate a systemic failure; in the chain of safety management, the same factors lead to both accidents.
The TCH and Oversight Authority play a prominent role but the roles of the operator should not be discounted either. Safety data collection from in-service aircraft and follow up and feedback to operators is supposed to be a closed loop which should mitigate potential catastrophic events.
With all the added regulations and procedures introduced in recent years (SMS Safety Management Systems) this accident still occurred.
Therefore the investigation should dive deep into the effectiveness of regulation and allow out of the box thinking pertinent to the existing regulatory structure and its monitoring.
Note that after a couple of (near) catastrophic events in the late eighties, (primarily the Hawaï 737 top fuselage separation), a global ageing aircraft drive was initiated with the emphasis on structural fatigue and corrosion management.
This involved renewed safety data collection and review, Service Bulletin Reviews and mandating terminating actions rather than repetitive inspections on Fatigue Citical Structure.
It also mandated existing structural repair evaluations and classification. This was supposed to successfully manage structural safety of all fleets globally.
The investigation should take this into account and recommend comprehensively on the effectiveness of the entire chain of responsibilities.
Below relevant source documents;
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