MD-11F Engine Separation: What the Preliminary Investigation Report Reveals

In this day and age of aviation, sudden structural failures are less common than they used to be, especially for fixed wing aircraft.

So when structural failures do happen, like this engine separation that UPS flight 2976 experienced on 4 November 2025, they hit very hard 💥

We’re going to cover what the preliminary investigation report reveals, what we can learn from it (while we wait for the full report), and what the remaining unanswered questions are.

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💥 Accident Overview

On 4 November 2025, UPS flight 2976, a McDonnell Douglas MD-11F (N259UP), crashed shortly after takeoff from Louisville Muhammad Ali International Airport.

Seconds after rotation, the left (#1) engine and pylon separated from the wing:

This ignited a fire, causing the aircraft to lose control, roll left, and impact the ground about 3,000 ft from Runway 17R:

The aircraft managed to clear the blast fence at the end of the runway, but the left hand side of the main landing gear struck a UPS warehouse.

The aircraft then made impact with a few other buildings, including a petroleum recycling facility.

All three crew members and 11 people on the ground were fatally injured. In addition to this, the crash caused a total of 23 injured people on the ground.

🔎 Investigation Findings

Engine + Pylon Separation

The investigation team confirmed that structural separation of multiple components of the left pylon to wing attachment was a key element to this crash.

The MD-11’s number 1 and 3 (the wing mounted) engines are attached to the wing via pylons. These pylons are attached to the wing with what the investigation refers to as a forward and aft mount:

This aft mount consists of an aft and forward lug, which is normally attached to the wing clevis via attachment hardware and a spherical bearing, like this (although the spherical bearing is obscured by the wing clevis):

The team managed to find this component at the crash site, and noticed that the forward and aft lugs (as well as the spherical bearing) looked fractured:

They examined the fractures, and found evidence of fatigue cracks and areas of overstress failure.

On the aft lug, both sides showed fatigue cracks starting where the bore meets the forward facing bit of the lug.

On the forward lug, the inside surface showed fatigue cracks too, but the outside surface broke purely from sudden overload (overstress failure), with no evidence of fatigue cracks.

Maintenance + Inspections

Another relevant note is that the aircraft had a total flight time of 92,992 hours and 21,043 cycles.

UPS’s maintenance program includes 3 main checks that covered the assembly mentioned earlier:

🔸 The left mount requires to be inspected every 72 months (6 years), which last took place on October 28th 2021 (4 years ago).

🔸 The pylon spherical bearing requires an inspection every 24 months, and was last completed on October 18th 2024.

🔸 A special detailed inspection was due at 29,200 cycles, and the left wing clevis support was due at 28,000 cycles. As the aircraft had 21,043 cycles, these had not been completed yet.

Similar Events

A similar event has happened before.

In 1979, American Airlines Flight 191 (a DC-10, which shares a lot of design principles with the MD-11) lost its entire left engine and pylon during takeoff in Chicago.

Part of the wing’s leading edge broke off with it. The aircraft initially climbed but immediately rolled uncontrollably to the left and crashed into an open field next to a trailer park.

All 271 people on board were killed, along with two people on the ground. The aircraft was completely destroyed.

This accident was fully investigated by the NTSB (Report AAR-79-17).

Flight Data Recorder / Cockpit Voice Recorder

Both the FDR and CVR were retrieved, and showed 63 hours of flight data, and about 2 hours of cockpit voice recordings.

They both stopped at 17:13:30 EST, which is consistent with the time of impact.

More details of these recordings were not shared in the preliminary report, but we’ll publish this when they are available in a follow up article.

💡 What can we Learn from This?

While the investigation is still ongoing, the findings here can teach us a few lessons:

🔸Metal fatigue remains a very relevant threat in modern aviation: The aft mount lug displayed fatigue cracking.

🔸 Legacy designs can carry legacy risks: The similarity to Flight 191’s failure mode is noteworthy.

🔸 The seconds after a structural failure are unforgiving in most cases. For this event, ADSB data shows the aircraft barely climbed, giving the crew no time and no performance margin to recover.

🔸 Ageing fleets might require evolving maintenance strategies: This airframe had 90,000+ accumulated flight hours and over 21,000 cycles, which is considered a lot for any commercial airliner.

🔸 Additional redundancy doesn’t always exist for major structural points: This continues to be the case for both fixed wing and rotary aircraft to this day.

🔮 What are the Unanswered Questions?

There are a few remaining questions that the preliminary report does not clarify or answer quite yet.

🔸 Why exactly did the fatigue crack occur?

🔸 Was it undetected overloading in the past, subtle alignment issues, corrosion, meterial degradation, or a manufacturing error?

🔸 Did the inspection intervals account for high-weight cargo operations?
🔸 What were the specific loading conditions during rotation?
🔸Are other MD-11 or DC-10 series aircraft showing similar fatigue issues?
🔸 Will the crew’s perspective on the CVR allow investigators to help find the root cause?

💭 Conclusion

This preliminary report shows that the MD-11’s No. 1 engine didn’t just break off by chance, there were fatigue cracks already growing inside the pylon mount.

While investigators still need to figure out why those cracks formed, it’s seems to highlight that even with modern inspections and better engineering, aircraft can still hide problems in high-stress areas.

What happened to UPS 2976 is a reminder that when a major structural part fails, it fails fast and the crew has almost no chance to recover.

As the investigation continues, the big questions now are what exactly caused the fatigue, whether the current inspection intervals were enough, and if other MD-11s might show similar signs of wear.

It’s a grim reminder that material fatigue is a threat that can still be very hard to manage properly.

You can find the preliminary NTSB report here.