The minimum speed required to be able to control a multi engine aircraft is the most critical engine fails is called Minimum control speed which has the ICAO standard abbreviation: VMC, meaning Velocity Minimum Control. The normal standard requirement in any commercial flight operations is that a runway is long enough so that the airplane can abort the takeoff run and stop on the runway before reaching VMC. In addition the aircraft should be able to climb above any obstacles during climb out. There are of course some margins regarding take of length and obstacle clearance in addition considering weather and runway condition and some leeway with regard to pilot handling. This is all described in the ICAO STOL manual. More details later.
Some of the Nepal airports could not meet these requirements due to terrain and hence didn´t meet the ICAO requirements. The runways were so short due to the surrounding terrain that take-offs had to be done without the ICAO standard. There were basically 2 ways: 1. Lift-off below VMC and hence having the risk of an engine failure below VMC when airborne which could lead to loss of control, i.e. that the airplane would flip around, or; 2. Lift-off at or above VMC and hence not having enough runway to stop if an engine failed late in the Take-Off run.
We did find ways to mitigate the above risks to an acceptable level, more to come!