Update: Monday Dec. 27 travel
Cancellations abating; weather may disrupt operations at SEA during mid-morning and PHL early evening.
Welcome to any new readers — we're grateful that you're here! We're building deep learning algorithms to democratize flight delay predictions; until we launch, we're eager to synthesize things manually in our outlooks. These feature several recurring themes that we recognize may be unfamiliar or intimidating, so we’ve written explainers that tackle airport arrival rates, queuing delays in the airspace and different tools to distribute those delays. If there’s a topic or mechanism you’d like to see unpacked, please let us know (same goes for special travel occasions).
We were relieved to open FlightAware this morning and find that Delta and United seemingly had cancellations headed in the right direction. After both airlines combined to cancel 550 Mainline1 flights scheduled to operate yesterday, they’ve managed to knock that down to 269 cancels today (as of Sun 8:00 p.m ET). While we expect today’s cancel count will inflate a bit as the day closes out, if yesterday’s trend holds, it should still finish around 275. To the airlines’ credit, they’ve stayed ahead of this about as well as could be hoped—at least operationally—with the cancellations generally input well before scheduled departure.
For their part, American continues to be relatively successful in keeping a lid on cancellations, with “only” 97 Mainline cancellations yesterday and 81 on the books for today (equal to 2% of their operation). We’re a little more reserved in our assessment of JetBlue, where no deterioration is apparent, but cancellation rates remain elevated. On an absolute basis, their 126 cancels today aren’t particularly voluminous (between Delta’s 165 and United’s 114 cancellations), however they operate a relatively small schedule—that smaller denominator means 12% of their operation has cancelled (Delta’s cancellation rate today is 6%, United’s is 5%). Southwest Airlines has entered the fray, having cancelled 68 flights today, though it represents “just” 1% of their schedule. With the exception of perhaps Mesa, regional carriers remain a relative safe haven and we’re just as surprised as we were in yesterday’s first look (which also revealed some geographic and aircraft type tendencies lurking in these schedule reductions).
Mon 09:00 a.m. ET update: Skywest, the nation’s largest regional carrier, really stumbled across the finish line yesterday, finishing atop the cancellation laggardboard (with 280 cancels). Winter weather at SEA yesterday, which makes up more than 2% of Skywest’s network, no doubt put upward pressure on cancel counts, though doesn’t fully account for the deterioration. It seems reasonable to assume Covid-related crew constraints have spread to Skywest; this is likely reinforced by their position atop today’s cancellation laggardboard as well (sitting at 183 cancels).
With a mostly improving cancellation picture, today’s outlook will shift back to a weather and air traffic focus. A steady barrage of Pacific moisture will combine with anomalously cold temperatures to produce wintry weather in the Seattle metro area. Meanwhile, a storm system that emerged from the Intermountain West this morning will bring precipitation to the northern Mid Atlantic. Let’s start off in the Pacific Northwest.
The most organized snow should occur today as an arctic boundary moves through, however the next system will already be passing by to the west tomorrow and could bring light snow for the afternoon and evening. SEA has been in and out of ground stops for much of today on account of deicing issues and surface conditions—we don’t expect that level of disruption tomorrow, though things may be slow to spool up as they recover from today’s disruption. (We don’t want an explainer to go to waste, though, so we’ll link to ours on winter operations.) Independent of recovery efforts, ceilings will need to be watched during the 10 a.m. hour, when 49 flights are scheduled to arrive. The TAF2 calls for ceilings to lift from 2,500’ to 5,000’ by mid-morning: if this verifies, we think there’s about a 1 in 4 chance for an arrival rate of 42 or lower. If a 42 rate is realized, delays would actually start in the 9 a.m. hour, though average length3 would be kept under 10 minutes4 when spread across all arrivals.
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We’d bet against an instrument that distributes delays so broadly, however, and think a first-tier ground stop is more likely (which focuses delay on arrivals originating from within 600 miles or so). We’ve modeled delays averaging 15 minutes for captured flights in such a scenario. Low to mid-level clouds linger throughout the day and 42 arrival rate would also be problematic in the 6 p.m. hour (44 scheduled arrivals) as well as 10 p.m. hour (when demand is front loaded). We anticipate miles-in-trail (MIT) could manage these later overages, in which case average delays are not modeled to exceed 10 minutes. MIT is more indiscriminate in where it allocates delays (i.e. first tier arrivals will absorb a more proportional delay), though can be difficult to track.
Weather models are in good agreement that much of Monday stays dry, as the approaching storm system initially runs into high pressure. Precipitation looks to be light when it arrives sometime during the afternoon; we’ll need to keep an eye on precipitation type, as some low probabilities for freezing rain nose into the area during the evening (otherwise rain expected).
Perhaps most interesting is the demand story that plays out in New York City this week. Airline schedules are strictly slotted at LaGuardia (LGA) and Kennedy (JFK) while they are “facilitated” at Newark (ultimately functions similar to slotting). Slot usage requirements at LGA and JFK are relaxed from December 24 through the first Saturday in January, however we’re not aware of any such exemption at EWR. For Monday, this has resulted in substantially reduced demand at LGA (down 34% week-over-week) and JFK (down 13%), while EWR schedules have only slackened somewhat (down 4%). For travelers transiting LGA or JFK this week, it should spell reduced delay chances; for travelers transiting EWR, it means more of the same.
Thankfully, 40 looks to be a reasonable arrival rate floor (less than 1 in 20 chance for lower rates), which limits downside. Nonetheless, with scheduled arrival demand between 37-42 in the 3 p.m., 4 p.m. and 7 p.m. hours, we expect some minor delays. Like the later overages in SEA, we anticipate EWR would be managed with MIT: we’ve modeled maximum delays of 10 minutes, though this low level of delay percolates for much of the late afternoon and evening.
Precipitation looks to start more like late morning in PHL. A rain/snow mix is possible at the onset of precipitation before a changeover to all rain by early afternoon. While clouds will be on the increase ahead of the precipitation’s arrival, we don’t expect capacity constraints for the 8 a.m. hour, when scheduled arrival demand peaks at 47. By 6 p.m. however, when 45 arrivals are scheduled, we think there’s at least a 1 in 8 chance for a 32 arrival rate. We’ve modeled a first tier ground stop for this case that produces average delays of 25 minutes for captured flights (with delays lingering into the 7 p.m. hour). A slightly more likely, though still bad scenario would call for a 40 arrival rate: we put chances around 1 in 4 for capacity reductions to reach this rate. A scheduled demand overage of 5 is a more marginal case as to what tool the FAA would reach for to administer delays, though we’ll want to keep in mind unforeseen unscheduled activity (see footnote 4). That said, we’ve modeled a MIT solution for the 40 arrival rate case that produces average delays of 12 minutes (spread across all flights).
Odds and Ends
There’s a few airports that we should mention, but didn’t warrant their own sections due to low predictability or low impact:
The arrival rate at Washington-Dulles (IAD) shouldn’t fall any lower than 62, which is equal to the scheduled arrival demand peak (in the 9 a.m. hour). IAD is busier than its peers, however, when it comes to unscheduled activity (see footnote 4), and total demand could conceivably exceed capacity in the 9 a.m. hour.
Snow and wind may constrain capacity at Aspen (ASE) as well as Vail (EGE), however the absence of historical data for these airports seriously inhibit our forecasting efforts. Unfortunately, the mention of a possible GDP is about the best we can do when it comes to prognosticating these ski airports.
A cold front—and accompanying band of snow—should push across the Salt Lake City (SLC) area during late afternoon. Accumulations don’t look to require snow removal such that airport capacity will be materially reduced, however deicing delays for departures should be expected while snow is falling.
Itinerary risk tomorrow isn’t as high as a glance at the national weather chart might suggest. We wouldn’t want to be totally carefree tomorrow, however, so we’ll be keeping an eye on mid-morning at SEA and early evening at PHL. In both of these cases, we’d really only be concerned about connections scheduled underneath 50—maybe 60—minutes and whose inbound flight originates from a close-in airport (i.e. within 600 miles or so). If this describes your trip, we think it’d be prudent to at least explore rebooking options. The good news is airlines have meaningfully improved rebooking flexibility by eliminating changes fees for most tickets (though a fare difference may still apply). We’ve linked to the same-day change policies for Delta (who operates a SEA hub) and American (who operates a PHL hub).
We’ll be back later this week with a look at post-New Year’s travel (as well as CES, if it stays on the calendar).
American, Delta and United operate their own flights, considered their Mainline operation (on larger jets, with upwards of 100 seats). These airlines also “purchase capacity” from regional carriers (e.g. SkyWest), wherein the regional carrier operates smaller aircraft (i.e. less than 100 seats) under the Mainline brand.
Terminal aerodrome forecast (TAF) is a format for reporting weather forecast information, particularly as it relates to aviation. TAFs are issued at least four times a day, every six hours, for major civil airfields: 0000, 0600, 1200 and 1800 UTC, and generally apply to a 24- or 30-hour period, and an area within approximately five statute miles from the center of an airport runway complex.
TAFs complement and use similar encoding to METAR reports. They are produced by a human forecaster based on the ground. TAFs can be more accurate than Numerical Weather Forecasts, since they take into account local, small-scale, geographic effects. Source: Wikipedia
While our modeling is aimed at tackling arrival delays, there's a strong correlation to departure delays (albeit with some lag and/or possible alleviation). Consider a scheduled "turn" at an airport: the inbound flight is scheduled to arrive at 2:19 p.m. and departs at 3:30 p.m. (71 minutes of turnaround time). Let's say the inbound is delayed by 40 minutes and instead arrives at 2:59 p.m. We'll further assume that the airline doesn't need the full 71 scheduled minutes to turn the aircraft and can accomplish the turn in 45 minutes if they hustle - the departure will push back from the gate at 3:44 p.m. (delayed by 14 minutes). In this example, a 40 minute arrival delay in the 2 p.m. hour is partially passed through to a departure in the 3 p.m. hour. Had the turnaround been scheduled at 45 minutes instead (i.e. no turnaround buffer), the lag between arrival and departure delay would still exist, however the delay would be fully passed through.
And of course, delays resulting from aircraft servicing, airline staffing, network effects, etc. should be expected (and are not included in our modeling).
Cargo airlines as well as private jets are not included in scheduled demand and only become apparent when they file a flight plan (generally day-of). This unforeseen demand introduces the risk that delay are under-forecast. Unscheduled demand added 9.6% to scheduled demand for Core 30 airports between 11/15/2021-12/14/2021. For the airports we’re considering today, PHL (added 17.7%) and IAD (added 20.1%) are above average by this measure . We’re working on a sub-model to predict unscheduled activity.