Why block time swings twenty minutes

Providence to Nantucket in a Meridian is 25 minutes one way and 31 the other on the same afternoon. Nothing changed but the wind. Here is how JetDesk knows before you do.

01The FB forecast

The FAA publishes winds and temperatures aloft (the FB product, still called FD by most pilots) for about 170 stations, at 3,000, 6,000, 9,000, 12,000, 18,000, 24,000, 30,000, 34,000 and 39,000 feet, issued four times a day with a use period of a few hours. JetDesk fetches the current issue for your region and keeps it for half an hour.

02From station to leg

For each leg, JetDesk finds the nearest forecast station to the midpoint of the leg, interpolates the wind vector between the two forecast levels that bracket your cruise altitude, and solves the wind triangle against your true airspeed. The result is a groundspeed, and block time becomes distance over groundspeed plus your block overhead. The leg card shows the wind used and its station so you can sanity check it against the briefing.

03Why it matters for fuel more than time

Six extra minutes is nothing on a schedule. Six extra minutes is four gallons, and four gallons is the difference between making reserve and not on a leg planned tight. The reserve check on every leg uses the wind-corrected burn, which is the point of the whole exercise.

04When the number is missing

Stations more than 300 nautical miles from the leg midpoint are ignored, and legs over the ocean or in the mountain west can fall outside coverage. When no station qualifies, the card quietly uses true airspeed and does not show a wind line. If you fly somewhere the FB does not reach, tune block overhead up a few minutes and treat the estimate as budget, not dispatch.

Open JetDesk →

More field notes

All field notes · Airport directory