In all the discussions about engine failure on twins, I'm surprised no one has yet mentioned Asymmetric Committal Height.
For the uninitiated, this is the height below which, if an engine has already failed or subsequently fails, you are commited to landing. For light twins it varies from 200ft AGL to about 400ft AGL. You are committed because below that height you are unlikely to be able to achieve a positive rate of climb before you reach Zero feet. The conditions I use and teach for descending below ACH (even with both engines working) are :
- On slope and centreline
- Runway clear
- Cleared to Land by ATC (if relevant)
- 3 greens.
If any of these elements are missing by ACH then prudence suggests a go-around. In some cases you might vary them (eg someone just vacating and obviously going to be clear), but the general rule is a sound one.
In some light twins, a failure below ACH with gear and landing flap will require full power on the good engine just to make the runway. For that reason, on a practice asymmetric approach I will not deploy landing flap until ACH is passed or all the above criteria are met (if earlier).
With regard to singles, it would be nice to be able always to reach the runway if the donk quits, but sadly the Nimbys and other issues make this impossible. It should be part of every approach to spot escape routes (football pitches etc) in case of dire emergency.