San Francisco to London: what really shapes the SFO-LHR corridor
- Departure
- San Francisco International Airport, San Francisco, the United States
- Arrival
- London Heathrow Airport, London, the United Kingdom
- Great-circle distance
- 8,616 km (4,652 nm)
- Typical airborne time
- 10h 31m
- Usual cruise levels
- FL340 to FL400
- Initial track
- northeast bound
Route overview
San Francisco to London is one of the longer regularly scheduled transatlantic flights, taking around ten hours and often flying a transpolar routing over Greenland and Iceland. The ride is usually calm, though a long trip crossing multiple jet streams brings its own considerations for those in the cockpit.
Why turbulence happens on this route
SFO to LHR routes generally cross Canada, pass close to Greenland, and then descend into Europe from the north. This transpolar or near polar routing exposes the aircraft to the polar jet stream twice, once over central Canada and again over the North Atlantic. Where the jet is strong and its edges are sharp, clear air turbulence can develop, particularly between the tropopause and the stratosphere. Unlike thunderstorm turbulence, this bumpiness is invisible on radar. Forecasters model it using upper air data and pilot reports. The high latitudes crossed on this route also mean occasional interaction with mountain wave activity over Greenland when strong westerlies meet the ice cap, and the Rocky Mountains at departure can add mechanical turbulence in winter storms. Aircraft flying this corridor are typically the 787 and A350, both known for smooth ride characteristics.
Which seasons are bumpiest
Winter, especially January and February, is the season when the polar jet is at its strongest and most disturbed, producing the most clear air turbulence on this route. Summer flights are usually smooth, though occasional convective activity around the Rockies at departure or the UK at arrival can add a short bumpy segment. Autumn and spring are transitional and typically comfortable. Because the route covers such a wide range of latitudes, individual segments can behave differently on the same flight. A crossing might be smooth over Canada and slightly bumpy nearing Greenland, or the other way round.
How pilots handle it
For a ten hour crossing we plan carefully around forecast turbulence charts, choosing an initial cruise altitude that avoids the strongest shear layers. Because the route is long, we typically step climb two or three times as the aircraft becomes lighter, which lets us stay in the smoothest air available. We monitor pilot reports on satellite messaging and coordinate with Gander, Reykjavik, and Shanwick oceanic control for altitude changes when needed. We in the cockpit watch the outside air temperature closely, since sudden temperature changes are a reliable clue that the aircraft is approaching the jet core and possible turbulence. The seatbelt sign goes on early when we expect any noticeable ride change.
What you can do as a passenger
On such a long flight, the best turbulence strategy is comfort planning. Choose a seat over the wing to minimise motion, and prefer aircraft you know are quiet riders, such as the 787 or A350. Both types damp turbulence noticeably better than older widebodies. Keep your belt fastened whenever seated. Bring noise cancelling headphones and try to sleep on eastbound overnight departures, which is when most SFO to LHR flights operate. Hydrate throughout, avoid alcohol, and eat lightly. If bumps do arrive, focus on breathing slowly and remind yourself the aircraft is fully in control.