At 5:15 PM on Tuesday, November 4, UPS Flight 2976 bound for Hawaii took off from Louisville Muhammed Ali International Airport in Kentucky. Louisville is the main worldwide UPS hub from which millions of packages are shipped weekly on aircraft such as flight 2976's three-engine McDonnell-Douglas MD-11. The MD-11 is somewhat of an orphan, as it was originally developed to be a wide-body passenger aircraft in competition with Boeing's 767. But only a couple hundred of them were built before production shut down in 2000 after Boeing acquired McDonnell-Douglas. As with most of the existing MD-11s, this one, owned originally by Thai Airways, was converted to freight service later, and was 34 years old at the time of takeoff.
Almost simultaneously with rollout, the left engine and its supporting pylon separated from the wing, and a fire broke out. An alarm bell went off in the cockpit, and for the next 25 seconds Captain Richard Wartenberg and First Officer Lee Truitt struggled to control the plane. But after reaching an altitude of only 100 feet, the plane began to roll to the left. It tore a 300-foot gash in a UPS warehouse south of the airport, left a blazing trail of fuel along its path, and collided with oil tanks at an oil-recycling tank, leading to explosions and a much bigger fire before the bulk of the plane came to rest in a truck parking area and an auto junkyard. Besides the three crew members including Relief Officer Captain Dana Diamond, eleven people on the ground died and about as many were injured, some critically. This was the most fatalities incurred in any UPS flight accident. On Saturday, the FAA temporarily grounded all MD-11s to perform inspections in case a mechanical defect is at fault.
This crash was one of the best-documented ones in recent memory, as it was in full view of a major road (Grade Lane), many security cameras, and numerous stationary and moving dashcams. One dashcam video posted on the Wikipedia site about the crash shows a blazing trail of fuel sweeping from right to left across the scene, engulfing trucks and other structures within seconds. An aerial view from south of the airport looking north shows what looks like the path of a tornado, as a wide swath of destruction leads from the runway to the foreground.
As the integrity of the support pylons is necessary for the structural integrity of the entire aircraft, aerospace engineers normally make sure that the engines are fastened really well to the rest of the plane. Typically, there are multiple points of attachment between the engine and the pylon, but the pylon itself is a structural member that is permanently affixed to the wing. While it's possible that the last time the engine was detached from the plane, somebody didn't finish the job reattaching it, because of the multiple attachment points it's unlikely that any mistakes would lead to the whole thing falling off.
Instead, my uninformed non-mechanical-engineer's initial guess is that fatigue or some other issue weakened the pylon's attachment to the wing, causing a crack or cracks that eventually led to the failure of the attachment point, which would let the engine and pylon fall off as they did. And it's natural that this would occur at a moment of maximum stress on the pylon, which occurs during takeoff.
Planes are supposed to be inspected regularly for such hidden flaws. But sometimes they can show up in inaccessible areas that might require X-ray or ultrasound equipment to detect. That is the main reason that the FAA has grounded the remaining fleet of MD-11s: so they can be inspected for similar flaws.
This early in the investigation, it's unclear whether the pieces of the aircraft will tell a definite story of what happened. It's a good sign that the left engine was recovered presumably without major fire damage near the runway, as the end of the attached pylon will give investigators a lot of information about how the thing came loose.
Inspections and maintenance are boring compared to design and construction, and so they sometimes get short shrift in an organization with limited resources. But there's an engineering version of the old saying, "the price of liberty is eternal vigilance." It goes something like, "the price of reliable operation is regular maintenance." I'm facing a much smaller-scale but similar situation here in my own home.
In Texas, air conditioning has become a well-nigh necessity, a fact recognized by everyone except the Texas legislature, which steadfastly refused once again this year to use some of the budget surplus to air-condition all Texas prisons. (Sorry for the soapbox moment, but I couldn't resist.) Anyway, every spring and fall I have an HVAC company come out and inspect our heat-pump heating and cooling unit. Last spring they said it needed a new contactor that was about to go out, and the fan motor bearing didn't look too good, but it was otherwise okay.
Things changed over the summer. Now the evaporator has sprung three leaks, the compressor has been working so hard that its insulation and capacitor are compromised, and to make a long sad story short, we need a whole new unit.
I could have just ignored matters till something major disabled the unit: the compressor shorting out, the fan motor freezing, any number of things. As often happens in such cases, it might have failed either in the middle of the coldest day of the year, or next August when the thermometer reads 102 in the shade. Not wishing for such emergencies, I choose to have regular maintenance checks, which have paid off, both for me and for the HVAC people who get to install a new unit under less-than-urgent conditions.
My sympathy is with those who lost loved ones both in the air and on the ground in the crash of Flight 2976. And my hope is that if lack of maintenance is found to be a contributing cause, that the grounding of the other MD-11s will prevent another accident like the one we saw last Tuesday.
Sources: I referred to an article on the FAA action at https://abcnews.go.com/US/final-moments-ups-plane-crash-detailed-ntsb/story?id=127313407, a comment on engine support pylons at https://aviation.stackexchange.com/questions/79872/what-are-different-components-of-an-engine-pylon, and the Wikipedia articles on MD-11 and UPS Airlines Flight 2976.
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