NTSB Preliminary Report – UPS Boeing MD-11F Crash [pdf]

Failure mechanics and fatigue

• Discussion centers on the aft and forward pylon mounting lugs: three of four fracture surfaces show fatigue cracking; the fourth is pure overstress, implying the aft lug failed first, then the forward lug tore in overload.
• Commenters parse the report and AVHerald diagrams: the engine stayed attached to the pylon; it was the pylon-to-wing lugs that failed.
• Several expect fatigue cracks of this type should be detectable with proper, timely inspections, raising questions about inspection intervals and access to the crack locations.
• The aircraft had ~21,000 cycles; a “special detailed inspection” of the aft lugs wasn’t due until ~29,000 cycles, so it was well short of the mandated threshold. Debate ensues whether that points to an underspecified inspection regime or just unlucky early fatigue.
• People discuss metal fatigue basics (endurance limits, non‑ferrous vs ferrous alloys) and note the failure looks “clean and brittle,” consistent with advanced fatigue.

Engine motion and forces

• One line of discussion attributes the engine’s “up and over” trajectory partly to gyroscopic precession of the spinning turbofan during rotation.
• Others argue gyroscopic effects are minor compared to simple thrust and hinge geometry: aft mount fails, engine thrust flips it over the wing, then drag and airflow drive it down.
• Consensus: gyroscopic forces may influence direction, but the motive energy is the engine’s own thrust.

Similarity to past accidents and safety culture

• Strong comparisons are drawn to American Airlines 191 (DC‑10): wing engine detaches during takeoff, strikes the airframe, catastrophic loss.
• Key distinction raised: AA191 was traced to improper maintenance that cracked the rear bulkhead; this case currently points to fatigue in the lugs, not obviously the same mechanism.
• Other reference points: El Al 1862 (747 engine/pylon failure), UA232 (DC‑10 uncontained failure destroying hydraulics), DHL Baghdad (severe wing damage yet controlled landing).
• Some worry about “backsliding” in safety and cost‑cutting in maintenance; others emphasize the rarity of such events and the age/lineage of DC‑10/MD‑11 designs.

Trijet design and survivability

• Multiple comments stress that airliners are designed to survive a single engine failure on takeoff; this event involved loss/damage of two of three engines plus major wing/fuel‑tank damage, making survival unlikely.
• The incident underscores non‑independence of failures in trijets (wing engine failure affecting the tail engine) and prompts debate whether the whole trijet configuration is now an obsolete, marginal design.
• Some note trijets originally solved 1970s engine reliability and ETOPS constraints; with modern engines and rules, big twins are preferred.

Grounding and fleet implications

• Grounding of remaining MD‑11s and DC‑10 variants is seen as impactful but manageable: almost all are cargo, firefighting, or specialized refueling aircraft; no passenger service remains.
• Speculation that fleetwide inspections, possible redesign/replacement of rear pylon lugs, and shorter inspection intervals will decide whether any return to service is economical.

Report access, formatting, and side topics

• Several comments note OCR artifacts and typos (e.g., misread acronyms) in the PDF, likely from scanning; NTSB later replaces it with a cleaner image‑only version.
• Users share updated NTSB links after the original URL breaks.
• Brief side-thread on AVHerald blocking Cloudflare/VPN IPs, and on the intensity of the surveillance and vehicle video showing how fast the accident unfolded.