System and method of operating multi-engine system

A system for operating a multi-engine system of a helicopter, the multi-engine system having a first turboshaft engine having a first shaft, a second turboshaft engine having a second shaft, and a gearbox having a clutch system clutching at least one of the first shaft and the second shaft to a common load of the helicopter, the first and second shafts having a range of rotation speeds defined as a placarded zone, the system comprising:

• a processing unit;
• and
• a non-transitory storage medium having stored thereon program code executable by the processing unit for:
• rotating the first and second shafts at a first idle rotation speed below the placarded zone when the first and second shafts are clutched to the load;
• increasing a rotation speed of the first shaft from the first idle rotation speed to a flight rotation speed above the placarded zone;
• unclutching the second shaft from the load during the increasing the rotation speed of the first shaft;
• increasing a rotation speed of the second shaft to a second idle rotation speed when the second shaft is unclutched from the load, the second idle rotation speed above the placarded zone and below the flight rotation speed;
• and
• maintaining the second shaft unclutched and maintaining the rotation speed of the second shaft to the second idle rotation speed until receiving a command to change an engine regime of the second turboshaft engine.

A method of operating a multi-engine system, the multi-engine system having a first engine having a first shaft, a second engine having a second shaft, and a gearbox having a clutch system clutching at least one of the first shaft and the second shaft to a load, the first and second shafts having a range of rotation speeds defined as a placarded zone, the method comprising:

• rotating the first and second shafts at a first idle rotation speed below the placarded zone when the first and second shafts are clutched to the load;
• increasing a rotation speed of the first shaft from the first idle rotation speed to a flight rotation speed above the placarded zone;
• unclutching the second shaft from the load during said increasing the rotation speed of the first shaft;
• increasing a rotation speed of the second shaft to a second idle rotation speed when the second shaft is unclutched from the load, the second idle rotation speed above the placarded zone and below the flight rotation speed;
• and
• maintaining the second shaft unclutched and maintaining the rotation speed of the second shaft to the second idle rotation speed until receiving a command to change an engine regime of the second turboshaft engine.