4 airlines fly nonstop from Seattle to London, 4,786 miles: British Airways, Delta Air Lines, Virgin Atlantic, and Alaska Airlines. The figures below come from the records every airline files with the U.S. government for each flight into or out of the United States.
Emptiest months on this route, all its airlines together: February (68 percent full), October (69 percent full), and January (70 percent full). Fullest: September (92 percent), June (91 percent), and August (90 percent). Months every airline here usually runs 80 percent full or less: January and February.
| Month | British Airways | Delta Air Lines | Virgin Atlantic | Alaska Airlines |
|---|---|---|---|---|
| January | 76 percent full, usually open | 68 percent full, usually open | 62 percent full, usually open | no load record |
| February | 79 percent full, usually open | 57 percent full, usually open | 59 percent full, usually open | no load record |
| March | 89 percent full, tight | 77 percent full, usually open | 71 percent full, usually open | no load record |
| April | 87 percent full, tight | 64 percent full, usually open | 65 percent full, usually open | no load record |
| May | 91 percent full, usually full | 72 percent full, usually open | 77 percent full, usually open | 64 percent full, usually open |
| June | 93 percent full, usually full | 93 percent full, usually full | 87 percent full, tight | 78 percent full, usually open |
| July | 89 percent full, tight | 78 percent full, usually open | 83 percent full, tight | no load record |
| August | 93 percent full, usually full | 87 percent full, tight | 86 percent full, tight | no load record |
| September | 97 percent full, usually full | 86 percent full, tight | 90 percent full, tight | no load record |
| October | 83 percent full, tight | 54 percent full, usually open | 60 percent full, usually open | no load record |
| November | 84 percent full, tight | 73 percent full, usually open | 68 percent full, usually open | no load record |
| December | 85 percent full, tight | 82 percent full, tight | 74 percent full, usually open | no load record |
Each figure is the average for that month across the recent years on record: usually open is 80 percent full or less, tight is 81 to 90 percent, usually full is over 90 percent. These are how full flights have run, not live seats, standby lists, or fares. Check with your airline before you travel.