Emergency start of a gas turbine engine

A starting apparatus for a first gas turbine engine of a plurality of gas turbine engines of an aircraft, the starting apparatus comprising:

• an air turbine starter configured to cause rotation of a spool of the first gas turbine engine of the plurality of gas turbine engines using compressed air derived from an air source external to the first gas turbine engine;
• an electric machine configured to cause rotation of the spool of the first gas turbine engine;
• and
• a controller configured to:
• receive an emergency restart command for the first gas turbine engine while the aircraft is in-flight;
• determine whether the first gas turbine engine is in operation;
• determine whether at least a second gas turbine engine of the plurality of gas turbine engines is in operation;
• and
• responsive to receiving the emergency restart command and determining that at least the second gas turbine engine of the plurality of gas turbine engines is in operation and that the first gas turbine engine is not in operation, perform an emergency restart of the first gas turbine engine by at least simultaneously causing the air turbine starter and the electric machine to cause rotation of the spool of the first gas turbine engine, wherein:
• simultaneously causing the air turbine starter and the electric machine to cause rotation of the spool of the first gas turbine engine comprises simultaneously supplying pneumatic energy to the air turbine starter that causes the air turbine starter to deliver torque to the spool and supplying electrical energy to the electric machine that causes the electric machine to deliver torque to the spool, and
• simultaneously causing the air turbine starter and the electric machine to cause rotation of the spool of the first gas turbine engine cause the spool to reach a threshold speed for a restart to be executed during the emergency restart relatively more quickly than only a single one of the air turbine starter or the electric machine.