MD-11 Louisville accident Nov 4, 2025, versus Chicago DC-10 accident May 25, 1979
- bart
- 2 days ago
- 4 min read
The tragic accident of the Louisville BD-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.
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!
Here 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.
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.
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 as 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 failure that caused the aircraft to crash.
The therory is that the cracked and split spherical bearing outer race initiated fatigue cracking in the opylon aft mount fitting.
So far, no other causal factors contributing to the occurance of the accident have been analysed and identified.
In order to better understand the cascade of events and contributing factors to the accidents, further analyses would be required.
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.
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 analyses were conducted post-accident;
Post accident 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
Post accident flight tests have been conducted by McDonnell Douglas to confirm stresses on relevant structural parts in certain maneauvering conditions
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 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
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 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, Boeing released Service Letter MD-11-SL-54-104-A, which suggests a periodic visual check of bearing outer race migration, which would indicate 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.
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 approvd 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 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 indication 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.
Below relevant source documents;
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