Excellent question, comrade. Here's the Party-approved method:
1. During the briefing - The CO must assign elements to specific transport helicopters AND give clear instructions on how pilots should expect to communicate with the leaders of carried elements. For example: assign a squad to each transport helicopter and ask pilots to join the squad's TS channel.
2. At mission start: If you are a ...
- Pilot - Get in your helicopter, but do NOT start your engine. ONLY start your engine when the CO orders you to do so (either directly over CC or as relayed by the leader of one of your carried elements).
- FTL - Order your troops into the assigned helicopter; be the last man onboard from your fireteam. When you are also onboard, inform your SL that your fire-team is safely loaded.
- Attachment Leader - Order your assistant(s) into the assigned helicopter; be the last man onboard from your element. When you are also onboard, inform the SL of the squad you are supporting that your element is safely loaded.
- SL - Do not board. Wait for your FTLs (and leaders of any attachments) to inform you that their element are safely loaded. Be the last man onboard, and then inform the CO that your squad (and any attachments) are safely loaded.
- CO - Wait for your SLs and other senior leaders to inform you that their helos are fully loaded. When you are happy that boarding is complete, order the pilots to start their engines and get airborne.