Why can’t I scroll through more than one aircraft at a time (MRX)?

MRX was designed to show one aircarrft at a time - the top priority, or primary aircraft. Additional aircraft are tracked, but are not as much of a potential threat than the three aircraft displayed. The primary aircraft represents the greatest threat to you. If this information was replaced, even temporarily, by a lesser threat, the greater threat may be overlooked. This would put the pilot at risk. MRX smartly manages traffic prioritizing so that the pilot doesn’t have to.