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We've transitioned our blog to Substack

  • Writer's pictureTim Donohue

[Thanksgiving 2021] Friday Nov 19 first look

We kick off our Thanksgiving 2021 coverage focused on Friday's flying. Travel behaviors are liable to have changed since last year, though Friday figures to be the third busiest "go" day if 2020's patterns hold (Sunday the 21st and Wednesday the 24th figure to be the second busiest and busiest "go" days, respectively); return traffic consolidates around Sunday the the 28th, which should be the busiest day of the entire period.

Readers of our previous disruption outlooks will know that we're building algorithms to automate and democratize the insights provided herein - until then, we're eager to synthesize things manually! There are a couple important differences we should highlight from previous disruption outlooks. We'll attempt to assess potential disruptions at across the country, which requires we trade breadth for depth. If we hear we've moved too quickly, we'd be happy to circle back to a particular concept or prediction. Perhaps more importantly, we focused only on arrival delays in previous exercises, given that we wrote them in conjunction with a special travel occasion. Travel is more omnidirectional in this case, however, and we recognize you may be originating from, destined for or connecting through an airport that we're examining. While we'll continue to focus on arrival delays at an airport, 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.

With that all that said, we'll still start with a survey of weather. Broadly, we'll be watching two features: another system will move across the Pacific Northwest Thursday evening into Friday morning, with the associated frontal boundary dropping south into California. Rain amounts look to be light at both Seattle (SEA) and San Francisco (SFO). Elsewhere, a front that stretched from the Great Lakes to Gulf Coast on Thursday will move southward over Florida on Friday, resulting in a chance for showers and thunderstorms at Miami (MIA).

We anticipate SEA will be able to maintain an arrival rate of at least 42, in which case we predict delays will be negligible. We've linked to a couple explainers for readers who might be unsure what an arrival rate means or how it's related to delays. Weather will only marginally support that 42 rate however, and it's possible a 38 rate is instead realized. If SEA delivers a 38 arrival rate, then the 43 scheduled arrivals in the 10 a.m. hour represent a material demand overage - we've modeled delays averaging 8 minutes for arrivals in the 10 a.m. hour in such a scenario. We think that falls short of requiring a ground stop and would likely be managed with airborne holding (maximum modeled delay is 16 minutes). We've linked to one more explainer that answers what a ground stop is. Drier conditions are forecast by afternoon, which should comfortably support a 46 arrival rate. If clearing is slower than forecast, however, it's worth noting that 43 and 46 arrivals are scheduled in the 6 p.m. and 8 p.m. hour, respectively. We should also note that we only have visibility into passenger airlines, so there's some demand associated with cargo airlines that is not included in our modeling; cargo activity is generally concentrated outside peaks of passenger activity, but there's nonetheless some risk that delays are under-forecasted.

Let's move on to SFO, where airline flight schedules have been slow to recover from COVID. SFO flight activity is still 33% off of 2019 levels - this is the largest gap among 30 core airports in the US. The economic and market implications of this trend are far beyond the scope of this blog, though decreased demand on the airport at least reduces the probability of delays. Scheduled arrival demand at SFO peaks at 33 (in the 9 a.m. hour) and we struggle to envision an arrival rate any lower than 36. While we're confident air traffic delays will be absent from SFO, it does provide an opportunity to make an important qualification: things like aircraft servicing, airline staffing, network effects, etc. can (read: will) produce some delays.

Coincidentally, MIA is on the opposite side of the flight schedule recovery spectrum - they are actually up 14% from 2019's levels (they are the only airport up year-over-two-year). Fortunately, MIA also enjoys a relatively high floor when it comes to arrival rates (52) and their impressive recovery has created an hourly peak of "only" 44 scheduled arrivals. Similar to SFO, we're confident air traffic delays will be absent from MIA, though we'll take the opportunity to make another qualification. Lightning is liable to create delays separate from any demand/capacity imbalance, as baggage handlers and fuelers are pulled inside (thus halting their workstreams).

We also want to mention Newark Airport, despite seemingly unremarkable weather. While building high pressure should provide mostly clear skies, winds veer to a northwesterly direction. Newark is not well-suited to a northwesterly wind direction, as it potentially requires the use of Runway 29. An entire explainer could be written about EWR's Runway 11/29, but for the moment we'll leave it this: when EWR is required to use 29 as its primary arrival runway (rather than an overflow runway), its capacity is reduced by approximately 2 arrivals per hour (from 40 to 38). A northwesterly direction is not problematic when speeds are underneath 10 knots or so (12 mph), as aircraft are not bothered by the relatively light crosswind. At speeds above 10 knots, however, the use of 29 as the primary arrival runway becomes increasingly probable. Winds speeds during the day Friday are forecast in the mid-teens, which puts the chance of a reduced rate at around 13%. If winds speeds overachieve and reach the upper teens or touch 20 knots, that chance climbs to 20%. Those 2 aircraft per hour would be most missed during the late afternoon, when a 38 arrival rate would produce average delays of 9 minutes (and a maximum delay of 19 minutes). Like SEA at the top of our outlook, we anticipate delays would be managed with airborne holding in this scenario.

Where does that leave readers traveling on Friday? Thankfully the guidance will be quite similar to that found in our other outlooks (eventually our luck will run out). Readers transiting SFO or MIA should expect no air traffic delays; readers transiting SEA or EWR may experience minor delays. For readers in the latter camp, we don't think this level of disruption warrants rebooking - adjusting your delay exceptions [under 20 minutes and dependent on time of day] should suffice. The only exception to this stance would be readers who are schedule to connect during delay prone periods in SEA or EWR - if your planned layover is less than 50 minutes or so, even a short delay could result in a missed connection. The good news for readers with a tight connection is airlines are progressively offering some rebooking flexibility. Airlines have eliminated change fees for most tickets, though a fare difference may still apply; additionally standby is increasingly free. Same-day confirmed change (SDC) policies are a bit too varied to generalize, so we've linked to respective policies for Alaska, American, Delta, JetBlue, Southwest and United.

We'll be back tomorrow with updated weather guidance!

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