Multi-modal gas-turbine engine starting

A system comprising:

• a first gas-turbine engine of a plurality of gas-turbine engines that are configured to propel an aircraft, the first gas-turbine engine comprising:
• a first propulsor connected to a low-pressure spool of the first gas-turbine engine;
• a first air-turbine starter of a plurality of air-turbine starters, the first air-turbine starter configured to rotate a high-pressure spool of the first gas-turbine engine;
• and
• a first electric starter of a plurality of electric starters, the first electric starter configured to rotate the high-pressure spool of the first gas-turbine engine, wherein the first electric starter is not independently capable of starting the first gas-turbine engine from rest while the aircraft is on the ground;
• a second gas-turbine engine of the plurality of gas-turbine engines, the second gas-turbine engine comprising:
• a second propulsor connected to a low-pressure spool of the second gas-turbine engine;
• a second air-turbine starter of the plurality of air-turbine starters, the second air-turbine starter configured to rotate a high-pressure spool of the second gas-turbine engine;
• and
• a second electric starter of the plurality of electric starters, the second electric starter configured to rotate the high-pressure spool of the second gas-turbine engine, wherein the second electric starter is not independently capable of starting the second gas-turbine engine from rest while the aircraft is on the ground;
• and
• one or more controllers configured to control the plurality of gas-turbine engines.