Happy 2024 everybody! If you flew this holiday season, you probably had nothing go wrong at all. That was the case for nearly everyone… except for those who flew Southwest to and from Chicago’s Midway Airport just before Christmas. I’ve seen some reports call this a meltdown. That’s laughable. But what went wrong is actually a very interesting story.
Looking at Anuvu data for December 16 through December 26 to cover the Christmas ramp-up, no airline but Southwest canceled more than 1 percent of flights. JetBlue and Spirit hovered around having 65 percent of flights arrive within 14 minutes of schedule (pretty good for JetBlue), but no other airline was below 75 percent. The big three were all above 80 percent. It was a good time.
Southwest, however, had more cancellations, so let’s unpack that by day.
Southwest Operational Performance Late December 2023
As you can see, Southwest was running a spectacular operation up until December 23, and that’s when things got ugly for three days. The airline canceled 134 flights on the 23rd, 299 on the 24th, and 110 on the 25th.
The problem child here was Chicago. On the early evening of the 23rd, dense fog settled in over the Chicagoland area. It was so dense that visibility was below minimums for safe operations at Midway, and Southwest had no choice but to take action. It first diverted the airplanes that were on their way before the fog settled. Then it canceled the rest of the day plus the early morning departures the next day. On the 23rd, 128 of the 134 systemwide cancellations touched Midway.
The next morning, the fog was still there, but the forecast was for it to lift by mid-morning. The Terminal Area Forecast (TAF) put out by the National Weather Service (NWS) at 3am CT on the 24th said that fog would remain until 9am and then it would lift. But the weather improved more rapidly than that. A look at the reported conditions (METAR/SPECI) for Midway that day shows that at 4:53am, fog had lifted and visibility was up to 2 miles. By 5:01am it was up to 6 miles, and then just before 6am it was still at 4 miles.
As I understand it, Southwest was hesitant to believe this, but after consulting with the NWS, it decided that the forecast was good enough that it could send flights toward Midway again. Oops.
By 6:30am, the fog was back with a vengeance and visibility was less than 1/2 mile. On top of that an overcast settled in at 200 feet. That overcast didn’t get above 300 feet until the 11:16am METAR which means it went a lot longer than planned. Those airplanes that headed toward Midway ended up diverting.
That day, Southwest canceled 299 flights but only 181 touched Midway. The rest were mostly downline impacts where those airplanes were supposed to go. This did cause a jam up at Midway, however. Airplanes eventually made their way in, but there weren’t enough gates. Usually, the taxi-in time at Midway for Southwest is around 7 minutes. On the 24th, the average for the day was just over 59 minutes.
The weather ended up being fine after that, but Southwest had to play catch-up. Would it be able to fix the operation or would this end like the last holiday season where it truly melted down and fell apart for days on end? In this case, it was the former.
On Christmas Day, there were only 8 cancels at Midway. The total of 110 cancels was residual damage from the day before, but the airline rebounded to operating 77 percent of the flights that did fly on schedule that day. By the 26th, only 4 flights were canceled through the entire system, though on-time performance has lagged somewhat and didn’t climb back above 70 percent again until the 28th.
This wasn’t a meltdown by any stretch. While I’m sure some things could have been handled better with hindsight, there was a real, safety-related disruption that Southwest couldn’t avoid. Midway is a huge station for the airline, and almost nobody else flies there. But over at O’Hare, the weather was marginally better. Why wasn’t there as much of an impact there?
The problem is that while O’Hare has multiple runways set up for Cat III landings using the Instrument Landing System (ILS), Midway’s best runways have only Cat I capability. What the heck does that mean?
The ILS allows airlines to make approaches with limited visibility. How “limited” the visibility can be depends upon a variety of factors Airports, aircraft, and crews all need to be approved to use each category of ILS, or it can’t be done.
The three categories — I, II, and III (subsets A, B, and C) — have different rules based on decision height and runway visual range (RVR). The decision height is the altitude at which the decision to land has to be made based on ability to see the runway. The RVR is how far a pilot on the center line of a runway can see the runway markings. Here are the basic FAA rules on each category:
- Cat I – Decision Height >200 feet, RVR >2,400 feet
- Cat II – Decision Height >100 feet, RVR > 1,200 feet
- Cat IIIa – Decision Height n/a, RVR > 700 feet
- Cat IIIb – Decision Height n/a, RVR > 150 feet
- Cat IIIc – Decision Height n/a, RVR n/a
The thing is, as I understand it those numbers will vary by airline, aircraft, etc. It can also vary by runway depending upon equipment. Frankly, I got far down this rabbit hole and then gave up. The point being, I believe Southwest’s minimum RVR at Midway is 3,000 feet, and it was below that for much of this time.
Meanwhile at O’Hare, Southwest can go down to an RVR of 600 feet, because O’Hare has runways with Cat II/Cat III capability. So why doesn’t Midway have that?
The big issue here is that Cat II and Cat III have requirements for runway approach lighting to enable low visibility approaches. And Midway just isn’t physically able to comply. Why not? Have you seen Midway?
Midway is a very old airport that is completely hemmed in by roads and neighborhoods. They were able to realign Cicero on the east and put some of the terminal on the east side, but the runways are where they are. And there isn’t room to put all of the required lights. Or shall I say, the Federal Aviation Administration (FAA) doesn’t have the appetite to do so because of what’s involved.
Here’s how the FAA explained it to me:
Establishing CAT II / CAT III approaches requires specialized equipment and clear areas that would call for significant land acquisition deep into residential neighborhoods and commercial areas around Midway Airport.
That’s understandable. And the reality is that this kind of dense fog that requires Cat II/III landings doesn’t happen all that often. I can’t imagine it being worth the disruption to the lives of residents and the expense. So when it just happens to fall right before Christmas, we just have to deal with it.
I realize this has been a very deep dive, but the point is that Southwest was impacted by something that almost no other airline faced. As usual, weather caused trouble, but this time, Southwest recovered just fine. While I’m sure there will be learnings from this that could have helped reduce cancellations and delays, the end result wasn’t bad at all, especially compared to what happened last year.
54 comments on “Blame the Design of Midway Airport for Southwest’s Holiday Struggles”
Interesting. I flew Southwest on December 24, LGB–ABQ–BWI, and was surprised to find that both flights were nowhere near full. If Southwest had a bunch of cancellations at Midway, wouldn’t they try to flow as many passengers as possible through other stations? Perhaps Albuquerque is too far out of the way.
Incidentally, both of my flights on the 24th were delayed, though I’m not aware that either of the planes touched Midway. Then again, I didn’t look too deeply into the history of these flights; I was just concerned about making the connection (which would have come down to the wire if the second flight hadn’t been delayed, especially after our aborted takeoff at Long Beach due to a runway incursion).
Cranky,
I always start my mornings by reading your inevitably superb ruminations, but you have overachieved this morning, even by your lofty standards. Lots of people, in the 80s and even into the 90s, thought that Southwest’s strategy of entering (and usually dominating) smaller, older airports that had the side effect of being close to the city centre of smaller towns (remember that even Dallas used to be a smaller city) was brilliant because 1. better on-time, due to less traffic at secondary airports and 2. greater convenience for passengers, as far as proximity went.
What people didn’t realize when they were pontificating is that newer airports, almost always farther out, have more room for just about everything, as you point out. Not only are runways further apart now, but the equipment, from radar/lighting/etc. is more as well as superior at newer, larger airports. Of course this isn’t a problem most of the time, but when it hits, it hits with a vengeance. Just read an interview with the director of the (necessarily corrupt) O’hare reconstruction, and you can see that the reliability of backup runways, with regards to varying winds, is dominant in the placement of the newer runways.
Let us also notice that older airports usually are at a relatively low height relative to surrounding neighborhoods, which is great if you want a giant detention pond to protect the neighbors. Most passengers, however, disagree with that viewpoint. Witness HOU invariably flooding, relative to IAH. As far as runways spaced too closely, look at United with SFO.
You have covered many seemingly related topics, and tied them together in one wonderful essay. Hats off, cranky!!
Great analysis and explanation.
The only thing I’ll add is that MDW is almost exactly a 1×1 mile block (with the exception of the terminal realignment, as noted above). That lines up with the traditional way that flatter land was surveyed & plotted in the Midwest grid pattern (sections every 1×1 mile, townships every 6×6 miles).
These days, a 1×1 mile airport (especially one not constrained by a river/way/water feature) is on the smaller side for mainline jets. That helps to explain why MDW’s runways run from corner to corner across the block, despite those runways not being as well aligned with the prevailing winds as might be preferred.
There is no CAT 2 approach at MDW. Best published approach is 4000 RVR. WN may have a proprietary approach slightly lower. These events at MDW are well known. When I was a dispatcher for ML (Midway Airlines) in the late 1980s we had the same issue. Every airline has an independent weather service provider like WSI to give them specific forecasts that may be different from the NWS. Tough decision making for the network director.
Surprised that when the fog became heavier MDW didn’t call in Rex Kramer!
“Sorry, Clarence. Latest weather report shows everything socked in from Salt Lake to Lincoln (Park).”
:-)
Captain… maybe we should turn on the searchlights now? No… that’s exactly what they’ will be expecting us to do.
Did most of the diversions just go to ORD? If so, most people could likely still make their connections? Origin pax would be out of luck, but Destination pax would still be close to where they wanted to go.
Outer Space – I don’t know specifically but I would imagine they went to nearby large Southwest stations. I don’t think Southwest has the excess capacity at ORD to get people on and off easily.
So here’s some perspective on that. Southwest only has 5 gates in ORD, and only goes to 10 of the 100+ cities that SWA operates. On Christmas Eve, many of those flights were full already so they couldn’t just easily transfer onto one of those flights. At MDW, SWA uses 30+ gates to over 60 cities. That doesn’t even include any potential crew legality issues that would occur or the logistics associated with it.
…..and those 5 gates in T5/M-Concourse are shared and rotate. NOTE: Long walk from TSA and a longer walk from aircraft to exit, located near Delta Gate M8
The layout of the airport, short runways, and close proximity to surrounding neighborhoods does not provide much room for error. Better safe than sorry.
Remember UAL Flight 553 in December 1972. Safety first
Side question – any idea for the issues at JetBlue and Spirit? Media here in Tampa was reporting that delays seemed to be due to ATC – more issues at FAA Jacksonville?
If you ever get curious about ATC constraints or see news reports like that, check out the National Airspace System Status ( https://nasstatus.faa.gov/list ).
If you scroll down and click on “View Full Operations Plan” (which is updated/reissued multiple times daily to reflect latest conditions) you can see details on constraints, including any ATC staffing issues that are causing (or that are expected to cause) issues. ZJX (the FAA Jacksonville ARTCC) and ZMA are the ARTCCs that cover almost all of Florida, so you may want to look for those areas, plus FL-area airports.
Thanks! I’ll check that out!
Only flew in and out of MDW once, about 20 years ago. I was struck by how close the houses are, just across the street. Brett, you are correct, this was not SW’s fault. Man proposes and God disposes, although perhaps it did offer SW ops the chance to review and tweek some processes to help in the future.
As for the comment re SW’s strategy of choosing smaller airports (earlier in its development life-cycle), well, that was a good marketing strategy. Everything does have its downside risks, though.
Great read. I also tried to go down the rabbit hole last week figuring out BOS ILS and diversions (737s, E70/E75s, even a DL A321) — it’s not easy to understand. Need a pilot to weigh in here.
(Also: why do BOS diversions go to SYR, ROC and BTV? Do they really need to go 45-60 minutes away? Seems like PWM and MHT would be easier. There was one to ORH, that makes sense.)
I was wondering about those as well.
Looking at the flight history for the tail number on a flight I took on a “Delta” (Republic Airways) RJ, I saw that earlier in the week the plane had diverted to BTV instead of landing at BOS. BTV is 181 miles from BOS, and about as far away from BOS as you can get and still be in New England, excluding Maine.
The only thing that I could figure (uneducated guess as a non-pilot) was that maybe the other (closer) airports in New England, such as PVD/MHT/PWM/BDL were also socked in, especially those closer to the coast (BDL & MHT aren’t that that close to the ocean, but still much closer than BTV/SYR/ROC).
Off the top of my head:
This is not like a GA aircraft arriving at their destination and having to go missed approach and divert. The diversions are not happening after arriving in the Boston terminal area, but while enroute. Probably before even starting the arrivals from the west that would pass by SYR, ROC and BTV, as well as ALB and BDL (GDM4/JFUND2). In point of time, the further stations are closer.
Another factor is airport / company facilities available – and how many other flights may have already arrived at any possible diversions site. More than just a few diverting aircraft can create havoc at even decent size airports like PVD, MHT, BDL or ALB.
Also; low visibility conditions can be very localized (as small as just one end of the runway) or very widespread (ie, the entire northeast) which would impact pre-flight alternate / in-flight diversion planning.
The whole process can be very dynamic and convoluted with seemingly endless parameters that need to be accounted for and considered to come up with not only the safest outcome, but also taking into account passenger and economic concerns. All with a hard limit on fuel available which very literally equals time available. If your’e enroute with only enough fuel to reach your desitnation, miss and proceed to your planned alternate with reserves(minimum required fuel) and you expect any further delays – you must come up with another plan of action.
Thanks, appreciate the insights.
I’ll have to look for a detailed breakdown on YouTube from a commercial pilot that explains how the pilots & dispatch determine the fuel & potential alternate airports for flights where they are expecting to encounter dicey weather.
It’s amazing how much traffic can flow through such a small footprint. I wonder if MDW is the most “efficient” airport by a standard of (passenger enplanements) / (airport land area).
Okay, now I’m curious.
LGA: 29.0M pax / 680 acres = 42,647 pax / acre / year
MDW: 19.9M pax / 650 acres = 30,615 pax / acre / year
DCA: 24.0M pax / 861 acres = 27.848 pax / acre / year
ATL: 93.7M pax / 4700 acres = 19,936 pax / acre / year
HND: 64.2M pax / 3761 acres = 17,070 pax / acre / year
Well, LGA beats it. Any other obvious candidates?
I was going to suggest BUR but then I DiD mY rEsEaRcH and realized how few passengers it has
Now I need to look up the busiest helipad in the country
Interesting question.
Busiest “helipad” (including airports with multiple pads) in terms of aircraft movements? My guess would be Fort Novosel (formerly Fort Rucker), where the US Army trains its helicopter pilots, but that’s not commercial.
In terms of commercial helipads, I couldn’t find a quick/definitive answer on that, but could be the downtown Manhattan helipad or a helipad in the Gulf that delivers roughnecks to the oil platforms.
BUR actually limits the airlines on how many passengers they can bring in
Correction: I’m getting BUR and SNA confused.
SAN is 663 acres – smaller than LaGuardia. Not sure what year you are using for total enplanements though.
Just getting the passengers / year stat out of Wikipedia.
So then SAN has:
22,009,921 enplanements (for 2022 from Wikipedia)/663 acres = 33,197 pax / acre / year
…which places it right behind LaGuardia but still ahead of Midway.
That (of course) begs the question about the most “efficient” single-runway airport, as SAN only has one, but LGA and MDW have multiple runways.
Thinking of small-footprint airports that may (but actually don’t) rank up there:
LCY 3.0M pax / 150 acres = 20,000 pax / acre (was 5.1M in 2019 or 34,000 pax/acre)
SNA 11.3M pax / 504 acres = 22,000 pax / acre
Could also go look at SAB, SXM and SBH, but doubt any of those rank.
In fairness, MDW performance when weather affects the Chicago area has actually been very good! Before ORD built new rwys and realigned existing ones my impression was that ORD performance was usually relatively poor, while MDW ran very well in poor weather situations. Nowadays, ORD has more than enough rwy capacity for most of these situations.
However, in response to some of the observations above, ORD’s ability to handle diversions is still very limited because of a gross shortage of gate space. While there are major expansion plans actually under construction, the place – especially T-5, where WN has its operation – is a shambles – it’s awful!
The fact that WN recovered well from the MDW snafu speaks volumes.
It is a commercial decision to operate into airports that are too small and not up to modern design standards, when there are nearby alternatives. It is also a consumer decision to purchase a ticket to such an airport. #BUR #DAL #MDW
Those who make such decisions must suffer the consequences. The rest of us will be in and out of DFW, LAX and ORD.
In other words… “they bought their tickets, they new what they were getting into…” etc… right?
Why are you lumping Love Field in with those? DAL has parallel runways well spaced, and one is short of 9000’ long.
It’s not at all unsafe.
Maybe reread my comment? I never said anything was unsafe.
I just said small, and not meeting modern design standards. MDW, DAL and BUR are relics of an earlier era. DAL is stuck being small because of litigation, but it was also supposed to close decades ago.
What isn’t modern about Love Field? It has well spaced parallel runways, easily long enough to land just about any plane. It has a brand new terminal with great facilities.
It is a very similar design to places like Fort Lauderdale, Indianapolis. Hartford, or Kansas City.
What’s not modern? It’s just intentionally kept with fewer gates to limit passenger traffic.
The only thing not modern about DAL these days is it can only handle CAT II landings. Better than MDW for landing capabilities but not as good as DFW.
BUR needs 1 mile vis to land and only on Rwy 8.
The biggest story of 2023 regarding airline operations was that on-time in the US was the highest in more than 5 years – going back pre-pandemic. After a rough summer, airline operations were near flawless during the fall and even the Christmas/NY holiday went very well. Yes, weather cooperated but airlines are better staffed and have more standby resources. While WN’s operations were a mess in December 2022, UA’s June meltdown was the worst the industry saw in 2023 and it was contained much faster.
Some of the ATC holds at MDW were WN staffing related so it wasn’t all airport capability related. The few other airlines that have flights there did not suffer the same rate of delays and cancellations.
Part of WN’s problem in situations like this is their linear scheduling system; there are crews and planes that arrive at MDW in the morning, flow thru the “hub” (base) and then continue for an entire day via “non-hub” and “hub” cities. WN does overfly cities at times but you can’t recreate the efficiency of the original schedule, including not having crews run out of time in a non crew base city.
WN’s business plan was built around using secondary airports, many largely abandoned as new, more modern airports opened but WN has managed to keep air transportation closer to many people because of serving secondary airports; HOU and IAH are on opposite sides of the city as are MDW and ORD. Only its home airport of Love Field is about as close to the larger major airport as are any two major airports in the US.
Since WN has had runway overrun incidents at some of its physically smaller airports, they know the risks and have hopefully reduced those risks.
Given the vast improvement over Christmas 2022, WN gets 3 gold stars.
It’s important to remember that Midway was originally built in the 1920s when air traffic was a fraction of what it is today and the aircraft were propeller driven.
Between ABQ-AUS, AUS-STL, STL-AUS, and AUS-ABQ flights (all on WN) between the 20th and the 27th, only the last two (26th and 27th late night) were delayed, each by an hour-ish. Guessing those were spillover from MDW, as I believe inbound A/C changed, resulting in the entire flight number being delayed from the get-go. Silver lining was both flights ended up on ViaSat-equipped, big-overhead-bin MAX8s, and the delays had far enough advance notice that we just left for the airport later.
Such is the risk of being a passenger on an airline that doesn’t do out-and-back routings, so fair enough.
I have to say, Midway is a lot of fun for small GA planes. I’ve landed there in Piper Warriors a couple dozen times. You take the “Blue Hotel Visual” by flying up Cicero to the big blue hotel (the Holiday Inn on the SW corner of Cicero and 65th), then turn 45 degrees left to land on runway 31 Left. It’s very important that you turn, because a Southwest 737 might be landing next to you on 31 Center.
Also, I’ve got a weather website that uses METAR data directly, with an intuitive URL scheme to see historical weather:
https://www.wx-now.com/History/KMDW/2023/12/24
Enjoy.
Do you remember the crash between a Cirrus and a Metroliner at Centennial airfield in Denver a couple of years ago? Parallel runways like that… the Cirrus missed that left turn at Albuquerque.
Very interesting article, I’ve always thought the compact nature of Midway made it a more efficient operation compared to ORD but clearly that’s not the case. I flew MKE>DEN late on Christmas Eve and the entire plane had 15-20 people on it, it was a wild experience. Fun crew though and everyone was in the holiday spirit.
ORD is not my favorite airport by a long stretch, but it is an extremely efficient machine in situations like this. That runway realignment project was one of the best investments a US airport has made in the recent past. Now if they could just figure out how to fix the terminals to add more gate space and reduce traffic jams on the ramp.
I flew MSN-ORD-SFO on United while Southwest was dealing with all of this at MDW and the most that happened was a 5 minute hold on the ground at MSN for flow control at O’Hare. Try doing that flying on a 10am flight from SAN-SFO when SFO has a single low cloud near the approach end of the 28s that will burn off by 1pm.
I nearly ran a full CRJ900 off a runway in MDW because of a false MU report showing breaking action “Fair” when it was actually “NIL.”
It was a late-night landing in heavy snow. As a flying pilot at the time, I recalled the 2005 SWA1248 MDW overrun and took all precautions. I landed five knots below ref speed, landed hard to dissipate energy near the edge of the runway 800 feet in front of the touchdown zone, and rapidly applied full braking & full reverse. Halfway down the runway, the other pilot asked me if I was breaking—we were both standing on the brake pedals. We came to a stop 100 feet from the end of the runway EMAS system. Turning the plane taxi off the runway so close to the edge was difficult.
If I had not briefed and performed any one of the above precautionary landing techniques the CRJ900 would have come to rest in the EMAS. We told the tower the airport breaking was NIL and the tower closed the runway for the night. The false tower breaking action report was attributed to no recent landings and someone driving a truck, slamming the breaks to test friction and either not doing the test right, or doing the test on an area of the runway, ramp, or taxiway with fair breaking while the overall runway friction coefficient was effectively NIL.
Instead of fighting continuous foreign wars, the USA should fund our domestic infrastructure more. MDW has serious operational limitations that pose an added risk and the airport should be expanded by 3,000 feet in all directions. Until such a change occurs, MDW passengers face added risk from the possible reduction of airline pilot qualifications that the Regional Airline Association is fighting so hard for.
I was with you til you went on about pilot qualifications.
Those extra hours that these guys are required to get now? I’m sure flying around with me in a (Cessna) 172 in beautiful weather, dry pavement, and light winds will make them safer pilots in bad weather. Won’t they?
That’s the myth. Somehow more hours will make a pilot safer. I disagree…because those hours are almost going to be teaching students in perfect VFR and without any issues to deal with.
I would rather require those hours (or something like them) in a simulator dealing with real world issues that commercial pilots face and flight instructors never do.
John G,
Part 135s don’t fly these 172 aircraft. CFIs may be instructing in C172 to build time, but the act of building instruction and managing the training progress of students in a C172 or any other light single or multiengine airplane brings tremendous predictive value and professional growth. In the case of MDW, a pilot who spends an extra 750-800 hours flight instructing—building the demographic pyramid of pilot training will build experience teaching short field landings, icing, and landing aircraft in the setting of MU reports.
Probably just going to have to disagree.
My experience is that the vast majority of the time these guys build is in VFR, doing slow flight, stall recovery, and touch and gos. Over and over.
I just don’t see how doing that again and again is anything that prepares you for a sudden realization once the wheels are down that there is no braking happening.
Or what to do when you are landing an A350 and a Dash 8 rolls right under you.
Not sure that 300 landings at some GA airfield with crosswinds under 10 knots, no clouds, no ice, and no passengers or scheduling issues is really going to make that much difference in an emergency.
But again, we probably won’t agree. Props to you for your quick reaction that kept your plane intact and having everyone walk away.
Given the state of augmented reality and headup displays, seems like “we don’t have the room for traditional Cat III equipment at MDW” shouldn’t necessarily be the end of the discussion, but more of a jumping off place to discuss if there’s more modern tech that could do the same thing without the same footprint.
It’s been a long time now since Alaska was able to land in Juneau in all kinds of crappy weather because of essentially, as I understand it, an augmented reality head-up display that allows them to thread the needle every time.
Just seems like it’s worth asking the question if maybe there’s not a more modern system that might be able to substitute for traditional Cat III.
Hi Cranky,
A question about Southwest operations: I’m currently in Austin, connecting between a Southwest flight from New Orleans (442) to a flight to Long Beach (2865). The two flights are operated by the same aircraft. I thought that when an aircraft continues in the same general direction, Southwest typically gives the segments a single flight number and sells it as a through flight, but this obviously isn’t the case here. Do you know how Southwest decides when to consider two segments as a through flight?
That’s a weird one, Ron. They usually do try to keep single flight numbers when the airplane continues going in the same general direction. I’m not sure why it’s not the case here.
Two further comments from a Chicago resident, and longtime WN customer at MDW.
1. The fog was very patchy. The previous night, I drove home from downtown to Lakeview* around 11:00 PM. Going 4 miles up Lake Shore Drive and another mile inland, we went in and out of deep fog four times. (And no, I didn’t take RVR readings.)
2. With its runways that intersect in the middle, MDW is essentially a one-runway airport. (Contrast with LGA, where the intersections are near the end, and they can interleave use of one for takeoffs, and one for landings….. carefully). And it operates pretty close to capacity during its busy blocks. Any weather significantly short of CAVU requires additional spacing, and can cause backups.
* For those of you ignorant of Chicago geography, think Wrigley Field.