Complex sentence: The 747-400's leasing, resale and salvage value has dropped steeply because it is relatively expensive to operate, and in most cases, it is being replaced with wide-body twin-engine aircraft.
Split into simpler sentences: The 747-400's leasing, resale and salvage value has dropped steeply because it is relatively expensive to operate. In most cases, it is being replaced with wide-body twin-engine aircraft.