reliabilty – The OM Blog by Heizer, Render, & Munson

Guest Post: The Dangerous State of Air Traffic Control in the U.S.

Temple U. Professor Misty Blessley brings up a very timely OM issue-air safety.

Newark Liberty International Airport (EWR) has recently experienced multiple air traffic control outages, during which radar and communication systems used to track aircraft temporarily went offline. These disruptions have lasted up to 90 seconds in several incidents. Flights into and out of EWR have decreased by approximately 35% as a result.

When an outage occurs, air traffic controllers may issue a ground stop, essentially a pause in departures, similar to a real-life game of “red light, green light”—for planes awaiting take off. While Module D of your Heizer/Render/Munson textbook introduces queuing theory, the real-
time queues at EWR are available here. In practice, incoming planes may be directed into holding patterns that resemble stacked racetracks in the sky.

However, when radar and communication systems go dark, there’s no safe way to guide aircraft into these stacks or maintain proper separation. Once communication is restored, controllers must work through the resulting queues to safely sequence and clear aircraft for landing. Outages lead to flight delays and cancellations while also raising serious safety concerns. How can the skies be stabilized?

Modernize Technology – Many Federal Aviation Administration (FAA) systems still rely on outdated technology, including some that operate on decades-old hardware such as floppy disks. The federal government is actively working to modernize these systems by investing in updated
software, hardware, and communication networks.

Support and Expand the Workforce – During the recent incidents at EWR, some air traffic controllers have taken trauma leave, underscoring the high-stress nature of the profession. The U.S. has been facing a persistent shortage of qualified air traffic controllers, due in part to limited training capacity—currently, only one FAA facility is responsible for training controllers. With low acceptance rates and rigorous requirements, meeting demand has been challenging. However, efforts are underway, including the involvement of new schools, to expand training opportunities and help grow the workforce.

Classroom discussion questions:
1. In Ch. 17, Maintenance and Reliability is discussed and Ch. 6 covers Managing Quality. What lessons can be applied to make the skies safer?
2. What domino effects are likely to ensue once the plane has safely landed? What do you think can be done to attract more air traffic controllers?

Guest Post: Safety and Maintenance at the DC Metro

Professor Howard Weiss, creator of our Excel OM and POM for Windows software, provides his monthly guest post.

The Maintenance chapter of your Heizer/Render/Munson text points out that “poor maintenance can be disruptive, inconvenient, wasteful and expensive in dollars and even in lives”. The Washington DC metro is a prime example of this situation. Last month, a DC Metro train derailed. Fortunately, only one of the 187 passengers was hospitalized. The derailment was caused because the original specifications for manufacturing the wheels for the most recently purchased cars, the 7000 series, were not correct. The new cars went into service in 2015 and have been received in batches since then.

The Metro agency had received approximately 470 7000-series railcars by the end of 2017, 610 by the end of 2018, around 730 by the end of 2019, and all 748 delivered by the end of 2020. Correspondingly, as more 7000 series cars entered the system, the failure rate on the axles has increased from .01% in 2017 to 1.3% in 2021. Typically, about 150 cars are in maintenance on any day but due to the derailment, all 748 of the newest cars were pulled from service causing the Metro to operate with only 22% of its fleet.

Your text notes that to improve reliability individual components should be improved. This was the case with the cars in that the specifications improved for the most recent batch of cars that were delivered. The book also notes that improving preventive maintenance is useful. This is what the Metro is now doing for the 748 cars removed from service.

Classroom discussion questions:

How might the Metro increase its car capacity during this inspection time.
What are the repercussions of the fleet being reduced to 22% of normal?

OM in the News: The Boeing 737 MAX and Reliability

The troubled (and grounded) Boeing 737 MAX, as widely reported, included a new system (MCAS) that automatically deployed when a single sensor detected the danger of a stall. MCAS strongly pushed the nose of the plane down, and pilots could not successfully countermand the activation unless they turned MCAS off. Astoundingly, writes MIT Prof. Arnold Barnett in OR/MS Today (Oct., 2019), “Boeing told airlines nothing about the existence of MCAS, let alone about the procedure to disable it.” Put bluntly, says Barnett, “MCAS was directly responsible for two fatal crashes, Lion Air Flight 610 in Indonesia and Ethiopian Airlines Flight 302.”

Why did Boeing initially say nothing about MCAS? The dependence on one sensor violates the principle of redundancy, under which no single failure can cause the loss of the aircraft. Boeing argued that redundancy did exist: the pilots (who were not even told of the existence of MCAS) were the backup system that would disable an improperly deployed MCAS.

There were actually 2 angle-of-attack sensors on the MAX, one of which did not affect MCAS. Boeing devised a cockpit warning light that would come on if the 2 sensors gave highly divergent readings. But a production error meant that the light that was supposedly a standard feature of the MAX could never come on, except when the airline customer bought some optional equipment. Boeing discovered the error in 2017 but did not mention it to airlines until after the first MAX crash a year later.

Now Boeing is fixing the problems with MCAS, with 2 sensors. If one detects a dangerous tilt while the other does not, MCAS will not deploy. But what if the erroneous sensor is the one that says things are normal? More prudent is the policy followed by Airbus, which uses 3 sensors and goes with the majority when there is disagreement. “Given that the feature is standard on Airbus planes,” writes Barnett, “it is far from obvious that having 3 sensors is infeasible or prohibitively expensive.”

Classroom discussion questions:

Which formula in Ch. 17 (Maintenance and Reliability) applies to this issue?
What impact on airline scheduling is the MAX grounding having?

OM in the News: Reliabilty and Maintenance Secrets of the Airlines

“Airlines are pouring lots of time and money into understanding fleet reliability,” reports The Wall Street Journal (Oct. 12, 2017). Delta put together a team of mechanics, engineers and data geeks to find ways to make specific types of planes less prone to breakdowns. American has renewed efforts to schedule flights so each type of plane performs better.

“It’s not necessarily the airplane itself. It’s how we’re operating it,” says American’s VP. If no planes are reserved as spares, fleets become less reliable. Small fleets spread out among multiple hub airports often suffer higher cancellation rates because there aren’t opportunities to swap planes. Time scheduled for routine maintenance can get crimped if the planes get to mechanics late day after day. In 2016 American had 6 different kinds of wide-body jets flying international trips from Chicago. Reliability suffered. When glitches hit, the airline had little ability to swap planes.

Summer reliability is critical for airlines. Among the worst-performing planes were United 747s, which arrived on-time an average 63% of flights during the past 2 summers. United says it has worked the last several years on improving the reliability of the wide-bodies to achieve better on-time performance. Wide-body cancellations are down 60% since 2014.

Delta’s technical data team can not only predict which parts are liable to break, but also redesign some parts to make them more reliable and add monitors to track the health of parts on older jets. Suspect parts get replaced proactively ahead of manufacturers’ recommended replacement schedules, dramatically cutting cancellations. In 2010, Delta had 5,600 flights canceled by maintenance problems. Last year breakdowns caused only 303 cancellations, and the airline has suffered only 70 so far in 2017. Delta also loads seven 40-foot trailers each summer and sends mechanics out with the equipment to small cities to create temporary maintenance bases for specific types of planes. Last summer they were positioned in 7 spoke cities to do preventive maintenance on planes parked overnight there.

Classroom discussion questions:

Why do reliability figures differ dramatically among airlines and plane models?
What is the “secret” to picking an on-time flight?

OM in the News: Airlines Still Mastering the Role of Technology

A Delta employee hands out snacks to passengers waiting to check in at Newark airport this week

Just as we have seen rapid advances in technology in the manufacturing sector (see Ch. 7), so do we see the critical role of technology in services. This week, for example, a power outage at Delta Air Lines grounded thousands of passengers, wreaking havoc on the carrier’s reservations system and drawing attention to antiquated technology that has plagued many airlines. The outage canceled hundreds of flights and snarled Delta’s efforts to alert passengers to the problems via its apps and on airline flight-information displays.

When departing flights can’t take off, tie-ups at hub airports follow because gates aren’t available for arriving flights. Further delays arise because planes and crews are out of position to follow the published schedule. It can take days for a carrier to recover and get all of its passengers to their destinations.

The technical problems will cost Delta millions of dollars in lost revenue and damage its hard-won reputation for reliability, reports The Wall Street Journal (Aug. 9, 2016). The meltdown highlights the vulnerability in Delta’s computer system, and raises questions about whether a recent wave of U.S. airline mergers that created 4 large carriers controlling 85% of domestic capacity has built companies too reliant on IT systems that date from the 1990s. Delta merged with Northwest Airlines 8 years ago.

These IT systems—which run everything from flight dispatching to crew scheduling, passenger check-in, airport-departure information displays, ticket sales and frequent-flier programs—gradually have been updated but are still vulnerable. Following the loss of power, some critical systems and network equipment didn’t switch over to Delta’s backup systems. Delta aimed to limit customer backlash, but customers unleashed their frustration with 43,000 social media complaints.

Classroom discussion questions:
1. What did Delta do wrong IT-wise?

2. Why is a technology error more damaging in an airline than in a restaurant or university?

OM in the News: Now Comes the Hard Part for General Motors

“Less than a month after General Motors announced it would recall 1.6 million cars because of a defective ignition switch,” writes The New York Times (March 10, 2014), “the automaker now faces an arduous task: fixing the cars.” The process, particularly for older vehicles like the ones G.M. is recalling, is time-consuming and requires many steps, from designing the new parts, testing them to make sure they solve the problem, finding and informing owners, and actually completing the repairs.

The company has just started to send out the recall letters with a stern, if unusual, warning: “Remove all items from your key ring, leaving only the vehicle key.” That is because if the defective ignition switch is jostled, or even if the key chain is too heavy, it can turn off the engine and the car’s electrical system, disabling the air bags. G.M. said it had linked the defect to 31 crashes and 13 deaths since it was first alerted to the problem in 2004. The letter also tells owners that the replacement parts “are not currently available.” G.M. said the supplier, Delphi, needed to prepare the machines that would make the part before mass production could begin. In some recalls, parts suppliers have already sold off those machines, making it even more time-consuming.

The G.M. recall is large, but it is one more than 900 recalls in the past 7 years, covering 50 million vehicles. While recalls are not unusual, the number of fatalities involved and the way G.M. handled this one stretching over the past decade has the potential to cost the company hundreds of millions of dollars in fines and possible legal damages, in addition to tarnishing its reputation. This is a great story to bring to your class both in the context of Chapter 17 (Maintenance and Reliability) and as an Ethical Dilemma in Chapter 5 (Design of Goods and Services.)

Classroom discussion questions:

1. Why did G.M. wait so long to recall a defect it knew existed for a decade?

2. Why is this recall going to be difficult?

OM in the News: Boeing’s Dreamliner Nightmare

By now, you likely know that the Federal Aviation Administration (FAA) ordered U.S. airlines to ground the Boeing 787 Dreamliners in their fleets until the lithium-ion batteries on the planes could be proved reliable. The FAA’s action, writes USA Today (Jan.17, 2013), came after Japan’s two largest airlines grounded their combined 787 fleets because an All Nippon Airways (ANA) plane had to make an emergency landing when the crew detected a battery’s burning smell.

The 24 Dreamliners flown by ANA and Japan Airlines represent nearly half the 50 that Boeing has delivered to airlines. More than 800 of the planes are on order. The Dreamliner is Boeing’s newest and most technologically advanced jet, and the company is counting heavily on its success; it is the first commercial aircraft to be made largely of lightweight, fuel saving, carbon composites rather than conventional aluminum and steel. Passengers like the airy cabins, large windows and comfortable humidity.

But the Dreamliner has had technological and supply chain problems from the start, which resulted in its being 3 years late in delivery. Last month, United Airlines and Qatar Airways had to divert or ground planes because of electrical issues. The 787 relies heavily on electricity and thus needs the large lithium-ion batteries to power it. Batteries, though, aren’t the plane’s only problem: On Jan. 8, a fuel leak on a Japan Airlines flight to Tokyo was detected before takeoff from Boston. On Jan. 11, cracks were spotted in the cockpit window of an ANA in Japan. The same day, another ANA flight was delayed because of an oil leak from an engine generator.

Boeing has said the 787’s reliability is “well above 90%.” As you teach reliability in Chapter 17, however, recall that the overall reliability of the Space Shuttle was .98–and, indeed, 2 Shuttles crashed out of 100+ flights.

How do passenger’s feel about the plane? “The uncertainty surrounding the Dreamliner makes it a plane that isn’t one that you can book and expect to fly reliably,” says one travel analyst.

Discussion questions:

1. What is the major operations issue facing Boeing right now?

2. What was the reliability of other technologically new planes introduced in the past 50 years?

OM in the News: NASA’s Last Space Shuttle Launch

When the final Space Shuttle launch took place on July 8th, an era of tragedy and triumph that dominated space travel for a generation drew to a close. I worked at NASA headquarters in the late 1970’s during the planning for the 1981 inaugural launch of Columbia, and always followed the program closely–to this day I can watch every launch from my backyard in Central Florida! In 1982, Prof. Paul Meising (SUNY-Albany) and I published four OM-related cases about the Shuttle, which appeared in earlier editions of the Heizer-Render OM text. They dealt with Shuttle reliability (Ch.17), astronaut assignment (Ch.15), forecasting demand (Ch.4), and ordering external tanks (Ch.12).

Looking back on the Shuttle program 30 years and 135 missions later, several facts stand out. First, with a 98% reliability rate (Rs=.98), one would expect a major problem every 50 launches. And indeed, with the explosions of Challenger in 1986 and Columbia in 2003, NASA was almost statistically due for a 3rd disaster. The Wall Street Journal (July 9-10, 2011) quotes Duke space historian Roger Launius as follows: “It was a magnificent failure. It was the most technologically sophisticated launch vehicle ever, but it never made human spaceflight safe, reliable, or economical”.

Launius was correct. Our 1979 forecasts at NASA for 500 flights within the 1st decade–basically a launch a week starting in 1986–were off by 90%. Our pricing structure assumed that private companies, foreign governments, and the Defense Dept. would cover all the bills as full-paying customers. We budgeted each launch at $15 million, when in reality the average cost rose to $1.5 billion–100 times the promised price. Now, as the Russians are charging us $20-30 million per seat to ride to the Space Station, a piece of American history draws to a close.

Discussion questions:

1. Was the Shuttle program a success overall?

2. Why did the program never reach its budget and schedule targets?