The zero-sideslip is necessary for a pilot to maintain control of an aircraft and have the greatest climb performance during an engine failure in a twin.
The critical engine on a multi-engine aircraft is the engine whose failure will result in the most adverse effects on aircraft performance and controllability.
An Emergency Locator Transmitter (ELT) is a battery-operated transmitter developed to locate a downed aircraft and is a component of the various emergency services available to pilots.