How turbulent is SFO-ICN typically?

Light to moderate. The strongest chop sits near the jet core, and crews plan cruise levels around it.

What is the best altitude to avoid turbulence on SFO-ICN?

Flying above the jet core, generally FL380-FL410, gives the smoothest ride. Below it the shear is stronger.

When is the best time of year to fly SFO-ICN?

Summer and early autumn, when the East Asian jet is at its weakest. Winter brings the strongest core winds.

What causes the turbulence on this route?

Shear at the boundary of the East Asian jet stream, the strongest sustained upper wind on the planet.

Turbulence forecast SFO → ICN. San Francisco to Seoul Incheon. SkyBriefing.

San Francisco to Seoul: what the SFO to ICN corridor looks like

Departure: San Francisco International Airport, San Francisco, the United States
Arrival: Incheon International Airport, Seoul, South Korea
Great-circle distance: 9,086 km (4,906 nm)
Typical airborne time: 11h 04m
Usual cruise levels: FL320 to FL410
Initial track: northwest bound

Route overview

San Francisco International Airport (SFO) in San Francisco, the United States, to Incheon International Airport (ICN) in Seoul, South Korea, is a great-circle distance of 9,086 km, about 4,906 nautical miles. At typical jet cruise speeds, and with an allowance for climb, descent and approach, that works out to roughly 11h 04m of airborne time. The great-circle track leaves San Francisco northwest bound and spends most of the flight in subtropical air.

Leaving San Francisco

San Francisco International sits on the bay with coastal hills on both sides. The summer marine layer and the wind pushing through the Golden Gate shape the climb out, and departures are turned over water early. The great-circle track leaves SFO northwest bound, and the first waypoint band of the flight sits close to 37.6N 150.2W. On a sector of 11h 04m, the climb to cruise takes roughly the first twenty to twenty five minutes.

The East Asian jet stream

Along the way the track passes over the open Atlantic and the open Pacific. The midpoint of the SFO to ICN track lies near 37.5N 2.0E, about 4,543 km from San Francisco, which is where the corridor spends its longest continuous stretch at cruise level. This corridor lies under one of the strongest sustained upper winds on the planet, the East Asian jet stream. Eastbound flights ride it and arrive earlier, westbound flights are routed around the core to avoid the headwind. The turbulence here is clear air turbulence generated at the jet boundary, and it is a well mapped, well forecast feature of the region.

Cruise altitudes on this sector

Ultra long sectors begin cruise lower, often near FL320 because of the fuel load, and finish two or three step climbs higher, up to FL400 or FL410. Choice of level matters because turbulence is layered: a change of two or three thousand feet often puts the aircraft into calmer air, and that is one of the first adjustments a crew will request.

Arriving into Seoul

Descending into Incheon means coming down through the edge of the East Asian jet toward a cold coastal boundary layer. That combination gives the arrival its character in the winter half of the year. Descent normally begins around 37.5N 154.2E, roughly 2,272 km before ICN, and takes about half an hour from cruise level to touchdown.

Seasonal pattern

The East Asian jet stream peaks in winter and weakens through the summer, so late summer and early autumn sectors are usually the smoothest on this corridor.

Flying this route with less worry

Turbulence on this corridor is a comfort issue rather than a safety one. Airliners are certified to handle loads well beyond anything the atmosphere produces here, crews are trained for it, and the seat belt sign is the tool that keeps the cabin settled. What this page adds is knowing in advance: the map and Calmness Score above use current WAFS forecast data for SFO to ICN, so you can see what to expect before you board.