What should aircrews do if part of the flight will be over water and out of gliding distance to land?

When preparing to fly over water and recognizing that the aircraft will be out of gliding distance to land, the most crucial step for aircrews is to sign out life preserver units. This action ensures that all crew members have immediate access to critical flotation devices, which can be life-saving in the event of an emergency water landing.

Each of these life preserver units is designed specifically for survival in water and is an essential part of pre-flight safety protocols when flying over large bodies of water. By ensuring that personal flotation devices are readily available, aircrews enhance their safety preparedness, which is vital when faced with the risks associated with over-water flights.

The other options may involve critical safety measures, but signing out life preserver units is the most direct and immediate action that directly correlates to ensuring survival in the event of an emergency situation over water.