Questions About UPS Flight 2976

 

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.

The Morani Bridge Collapse: Style Over Substance?

Riccardo Morani (1902-1989) was an Italian civil engineer and bridge designer who was one of the earliest proponents of designs that used mainly prestressed concrete, rather than mostly steel.  In 1967, a bridge he designed was put into service in Genoa, Italy.  It spanned a river, some railroad tracks, and other portions of the city with three tall pylons, each of which had concrete stays reaching diagonally down to the roadway, which was suspended some 145 feet (44 m) above the ground.  It came to be known as the Morani Bridge, after its designer.

On Tuesday, August 14, during an intense rainstorm one of the tower-supported sections of the bridge suddenly collapsed.  As of today (Aug. 26), a total of 43 people have died as a result of the accident, not to mention injuries and property damage, which will total in the millions.  Government officials have called for the revocation of the contract with Autostrade per l’Italia, the private firm that handles highway maintenance in Italy.  One mourner at the state funeral held for many of the victims said that “In Italy, we prefer ribbon-cuttings to maintenance.” 

Engineering experts consulted by the media all said it was too soon to draw any conclusions about what might have caused the bridge to fall.  Bridges designed by Morani have a history of requiring more maintenance than more common designs do.  The stark elegance that may have appealed to clients around the world who were looking for something distinctive to add to a city skyline was achieved at a cost of asking a lot of the material that was used in the bridges Morani designed.  As we have mentioned before, pure concrete has almost no strength in tension, so to use it as a structural material, it has to be reinforced with steel “rebars” and other components that can withstand pulling stresses.  This would be especially true of the stays that slanted down from the tops of the towers to support the roadbed.  Over time, corrosion can attack these tension members, sometimes invisibly deep within a vital member of the structure. 

The evidence of why the bridge collapsed is buried inthe huge piles of rubble that workers will need to clear meticulously and carefully, and because such work is both a huge project on its own and demanding of attention to detail, it may be months or even years before we have an answer to the question of why the bridge collapsed.  After a bridge in Minneapolis collapsed in August of 2007, it took over a year for the U. S. National Transportation Safety Board to issue its final report on the accident, which attributed the collapse to a design flaw that made a gusset plate too weak. 

The problem with forensic investigation of prestressed-concrete bridges is that concrete is a much more complex material than steel.  Unlike steel, which is fabricated under carefully controlled conditions in a steel mill, concrete is often formed onsite, and the way it is mixed, poured, and treated after pouring can influence its ultimate strength and other properties.  Nevertheless, most prestressed-concrete bridges withstand the stresses they were designed for, and so the reasons for the Morani collapse will be interesting to discover, if they can be found.

While we still do not know whether the collapse was due to an initial design flaw or faulty maintenance, the question of maintenance for bridges and other vital pieces of infrastructure is an urgent one that industrialized nations all around the world are struggling with.  In 2017, the American Society of Civil Engineers (ASCE) gave the U. S. a D+ in its “infrastructure report card,” saying that 56,000 bridges (about 9% of the total) were “structurally deficient” in 2016.  While the situation has not reached such a crisis that we see bridges falling down every month, tragedies like the Morani collapse remind us that the price of deferred maintenance is sometimes much higher than anyone would like to pay. 

It’s a little bit like preparing for war.  The only way you know you didn’t spend enough money on preparing for a war is if you lose it.  You can win with barely enough resources, or with three times more resources than you need, and the result is the same.  The art and science of maintenance consists in doing enough to prevent nearly all major tragedies and to do something about minor problems fast enough, while not simply wasting resources on painting a wall that doesn’t need painting, for example. 

Judging by the rarity of bridge collapses, most bridges were either built well enough to start with to survive many decades with whatever maintenance they’ve received, or have been maintained well enough to keep standing.  But the shock value of a major bridge collapse is one of the main motivators for public funding of infrastructure maintenance, which has none of the appeal of new construction. 

Engineers are mostly used to working out of the limelight, doing dull but necessary things like scheduling expensive maintenance that takes money away from more flashy and popular government activities.  Riccardo Morani was somewhat an exception to this rule, attaching his name to striking bridge designs that caught the eye of the public time after time.  If there’s the equivalent of an Internet connection wherever he is, I’m sure he’s sorry to see what has happened to his creation in Genoa, whether the failure is due to him personally or due to insufficient maintenance over the five decades the bridge has carried traffic since it opened.  But maintenance is a job for the living, not the dead, and engineers in charge of maintenance owe it to their constituent publics to be sure that tragedies such as the Morani bridge collapse don’t happen.  We look forward to finding out what went wrong in Genoa a couple of weeks ago, and applying those lessons to future problems so that they can be avoided before more people get killed.

Sources:  I referred to news reports on the accident carried by Time’s website at http://time.com/5367757/italy-genoa-bridge-collapse-death-toll/ and The Guardian at https://www.theguardian.com/world/2018/aug/14/unusual-span-of-collapsed-genoa-bridge-had-seen-frequent-repair-work.  I also referred to Wikipedia articles on Riccardo Morani and the I-35W Mississippi bridge, and the ASCE report card at https://www.infrastructurereportcard.org/.