The time printed on a boarding pass is when the gate is supposed to close, not when the aircraft lifts off. The author of this post learned that distinction the direct way on a recent San Diego to San Francisco flight: the departure was delayed, the sun had moved by the time the plane was airborne, and the right side of the cabin would have been the better choice, not the left.
The seat had been picked using FlightSide's recommendation for the scheduled time. The recommendation was correct for that time, but wrong for when the flight actually departed.
How far off can it be
The boarding pass time and the takeoff time are separated by at least two things: gate delay and taxi time. The Bureau of Transportation Statistics tracks departure delays across U.S. routes. About 28 percent of flights run 15 minutes or more behind schedule. Among those, most delays fall under 45 minutes, though a long tail of multi-hour delays pulls the average well above that. Averaged across all flights, delayed or not, the gap between scheduled departure and actual pushback runs around 23 minutes.
Taxi time adds to that. Even a flight that pushes back exactly on time will typically spend 10 to 20 minutes on the ground before the wheels leave the runway, sometimes more at a busy airport.
The sun moves roughly 15 degrees per hour. A 30-minute gap between the scheduled time and actual takeoff is about 7 degrees. Near the moments when the sun is roughly aligned with the direction of travel, that shift is enough to move it from one side of the aircraft to the other.
What FlightSide does now
FlightSide now shifts its sun calculation forward from the scheduled departure time by a small buffer, applied to every flight automatically. The buffer is intentionally conservative: it covers a typical on-time flight's gate-to-runway gap.
For longer delays, a slider appears next to the Clear button once your flight details are filled in. Drag it to 30 minutes, or however long the airline's app says you are sitting at the gate, or maybe just whatever matches your expectation, and the recommendation and percentages update immediately. The scheduled time on the form stays unchanged. The shareable link continues to encode the scheduled departure. Only the sun calculation shifts forward.
The calculation has always been sensitive to timing. This change makes it accurate to when you are actually in the air, not just to what the airline printed.
Also in this update
FlightSide is the kind of app you open in situations where the connection is not helping you: at a gate with WiFi falling over, on a roaming plan that throttles after the first page loads, or mid-layover with one bar and a seat to pick before the window closes.
Getting that to work reliably is harder than it looks. The map is the expensive part. Tiles need to arrive, render, and match the route before your attention moves on. The previous version handled this well in good conditions and less well in bad ones.
Return visits now open with a world outline already on screen before the network has responded. The route and recommendation draw over something instead of over grey. Detail fills in as the connection allows, but the picture is never blank while you wait for it.
The app is also more careful about background work it does between visits. It used to refresh a wider range of zoom levels after install and on return visits, which is useful when conditions are good and wasteful when they are not. It now checks before doing that, and holds off when conditions are poor.
Try it
Pull up your next flight and run the recommendation twice: once for the scheduled departure, and once with 30 minutes of delay. If the recommended side changes, you have found a route where timing matters as much as direction.