As always, love the tool and thank you for putting so much effort into this. I start with this tool for so many trips. There's a few shortcuts I propose:

F4 (standard windows shortcut selects drop down menu, e.g., in explorer; or ALT+D in internet browsers)

Ctrl+U (or something to select "CUSTOM" selection of airlines in drop down; this is used so frequently)

Ctrl+D (to define the options: range; used much more frequently now with distance-based programs)