The Iron Sky Squadron warscroll battalion consists of 2-9 Arkanaut Companies and 2-9 Frigates. The Arkanauts and Frigates are all part of the same battalion, so they can be dropped at the same time if desired. Due to transport rules, you can opt to deploy units inside the frigates. These also count as one drop. So if I were going to do a one-drop (again, space out your drops if possible while still guaranteeing 1st turn initiative), it would usually go like this.
Declare deployment of the Iron Sky Squadron.
Frigate 1 carries Company 1, Khemist, Navigator
Frigate 2 carries Company 2, Brokk, Endrinriggers (Brokk and Endrinriggers also do not count against transport capacity due to Hitchers rule)
Company 3 deployed for maximum effect, either to claim an objective or maneuver into sniping position.
Because the three units physically on the board at the start of turn 1 are all part of the battalion, this can be done as a single drop.