’Tis the Season of Flight Delays

I am writing this short article as news of Omicron, the new COVID variant, emerges and countries worldwide are already placing travel restrictions. 

However, I was already planning to write this article, anticipating the major travel disruptions we would be experiencing this holiday season, even without new strains.

Let’s take a look at what happened during Thanksgiving. According to the Sun,

“American Airlines have hundreds hiccups on Wednesday and again on Thanksgiving, with 56 cancelled flights and 471 delayed flights over the last two days, according to the flight-tracking website FlightAware.”

In their response, American Airlines said that there weren’t “any major operational issues this week while carrying a lot of customers given the Thanksgiving holiday.”

Can they both be right? 

From the customer’s point of view, any delay during the holiday season is a terrible disruption. From the airline’s point of view, this is really a small incidence compared to the 1,200 flights that were canceled a month ago. 

But travel delays and flight cancellations are not the only disruptions. Over the last few weeks, I got more schedule change emails from airlines than I have received in total throughout the last decade (I am not exaggerating…I counted). 

For example, American Airlines changed a direct flight from Philadelphia to Salt Lake City, and added a layover in Chicago. The time change and short transit in Chicago (in the winter, no less) made the flight impossible. So I ended up canceling the flight altogether, and re-booking with a different airline. 

In another case, I only noticed the change when looking at the app about another flight. When I called and asked why I didn’t get a notification, the very nice and apologetic customer service representative was alarmingly honest and said that the changes were just too many to keep up with the emails. 

Some of these changes happen before the flight, and while they cause quite a bit of inconvenience, they at least allow customers ample time to be annoyed, vent, and ultimately reschedule. But the changes that happen in real-time cause significant pain, especially when they occur around or during the holiday season. 

Of course, these two types of disruptions are not unrelated in their root cause, which is why I actually anticipate significantly more flight delays this coming season. 

Air Travel Disruptions

Even during calmer days, airlines have never been known for handling travel disruptions well. Whenever there are delays, they can most certainly expect long lines in front of their customer service desks. 

Several years ago, my family and I traveled to Israel, along with our dog. We lived in Chicago and traveled through JFK (on the way to Israel) and Newark (on the way back). On the way to Israel, flight delays resulted in my dog being stranded at JFK for 72 hours while I was still in Chicago (the vets there took good care of him, so no worries). On the way back, we missed the connecting flight, and spent 14 hours in Newark with two kids, a dog on a leash, and 10 pieces of luggage. In both cases, minor travel delays caused a great amount of inconvenience. 

What exacerbated the issue was the fact that we traveled with two different airlines, El Al and Delta (which still collaborated, at the time). 

Following that experience, we never flew with our dog again, and I didn’t travel with El Al for another ten years. 

But this is not to say that other airlines are much better. 

The point is that, as long as planes are airborne, running an airline is easy. There is not much to do or worry about. Pilots follow the route they have been allocated, passengers more or less take care of themselves in terms of food and drinks, the plane stays clean enough without additional efforts, and passengers are always reminded to check that no personal belongings are left behind.

But planes cannot remain airborne forever, and the rest of the travel process has multiple steps (handoffs, layovers, catering supplies, refueling) which are linked to one another. These links, however, are potential breaking points in the process which only increase the likelihood of disruption. And the more these links break, the bigger the magnitude of the disruption. 

Why are Things Only Getting Worse?

Since COVID, airlines have gone (and are still going) through difficult times. The travel restrictions between countries, the risk of getting COVID on a flight (something that has not yet been resolved), and the fact that business travel has not fully resumed, are all real problems airlines have had to deal with.

And indeed, as demand decreases, airlines cancel more flights, which means that the overall capacity becomes tighter. During the early days of COVID, flights were quite empty. This is no longer the case. If you have traveled recently, you would know, as the following graph shows, that the load factor is increasing. 

Load factor is the percentage of the utilized capacity of an airline’s seat miles. At the beginning of the century, the load factor was approx. 70%. This rose to 85% for the majority of the decade, and when COVID hit, it dipped to approx. 15%. As the panic around COVID subsided, it increased to almost 50%, from July 2020 to April 2021, and with a steady vaccine rollout, soared to 85% in July 2021. 

The implication of high utilization is twofold: when a flight is canceled, the passengers need to be reassigned. But the existing flights are already quite full, which makes it hard to reassign those whose flight was canceled without disrupting those whose flights were not. 

But recently, we had one more layer of disruption: Airlines are facing a new pilot shortage as planes, but not personnel, return.

“...experts expect the return of a more structural pilot shortage in the coming years as flight operations eventually ramp up to 2019 levels but without the pilots who took advantage of early retirement offers put forward by airlines in 2020.”

And the reason (among many):

“Fueled by a surge of pilots reaching the mandatory retirement age of 65 and augmented by industry growth and a reduction in the number of military-trained pilots who could quickly be hired, the U.S. airline industry was struggling with a pilot shortage prior to the pandemic.”

Notice the similarity with the supply chain world: Fewer pilots, fewer flights, more country-mandated bans, restrictions, and border closures, increase volatility. And who is going to suffer: the travelers and their families.

The Root Cause

Flights are like supply chains, and not only in terms of the number of links and stakeholders in the process. They also have one more characteristic in common: as they reach capacity, they react poorly to disruptions. 

This is explained by one of the main concepts in The Goal, my all-time favorite operations book: the effect of the combination of statistical fluctuations and dependent events.

The notion of dependent events is that in every operating system, you need multiple steps to accomplish a task. These steps usually depend on each other. For example, a flight can leave only after the previous flight has arrived. 

The notion of statistical fluctuation is best explained as variability. Given airport congestion and weather, every flight has some variability in its length. 

However, the main point is that the combination of the two really exacerbates the impact of variability, resulting in the system never achieving its actual capacity.

Why?

If there was only one link (e.g., one flight a day), we could expect some variability in the on-time arrival. But some flights would arrive ahead of time, and others would arrive late, so on average, things would balance out and be ok. 

Since all flights using the same plane are linked, this averaging cannot happen. If a flight arrives ahead of time, because the leg was shorter due to tailwind, for instance, it still has to wait until the scheduled departure time. The airline cannot keep an inventory of this “excess time.” However, when a delay occurs due to a headwind or congestion on the tarmac, all subsequent flights will be delayed. 

In fact, the tighter the system is, the more amplified the small disruptions become. The system just doesn’t have enough of a buffer to recover from them. 

In order to mitigate this, traditionally, airlines have used schedule padding. They could also opt for a lower load factor, but as shown above, this is not the case anymore. We are back to pre-COVID levels, but with fewer flights. 

And the impact when utilization is close to 80-90% is quite dramatic:

This graph is borrowed from queueing theory, but can be used to explain many of these phenomena. An increase of utilization from 80% to 90% means more than doubling of the waiting time.

All this shows me that things are not just going to get worse, they are going to get much, MUCH worse. 

My advice?

If you are planning to travel this holiday season, apart from your personal belongings, make sure to also pack ample patience, and go to the airport with an adventurous mindset.