Boeing Field is closely aligned with the extended centreline from SeaTac. If you approach SeaTac from the north and sit on the left side of the plane, you can look almost straight down on the field. Similarly, if the departures are heading northerly, it routes nearly over Boeing Field. For most flights, they are already high enough that they are not a good photo target. The heavies provide some interest though.
First, they are bigger so a slightly easier thing to fill the frame with. More importantly, they tend to be a bit more leisurely in their climb rate so are a bit closer in as they pass over. While I won’t bother to shoot the majority of the passing traffic, the heavies will often get my attention – provided nothing else is happening in front of me. Here are some of the recent passers-by.