It all depends on the engine service plan you enroll the engines on when you purchase the aircraft. The service plans require SOAP samples be taken at specific intervals (150-300 hours) to ascertain the "health" of the engine. Garrett engines are very reliable, but programs like MSP
, JSSI, ESP, and others can specifiy the SOAP interval. This however is NOT a chapter 5 item and therefore is not a required maintenance task.
P&W has ESP (Eagle Service Plan) if I remember ( I maintained Lear 60-235) there were SOAPs required to be in the Gold ESP......but it's been a few years now. Pratt has issues brewing with the 300 series engines, such as the HPT blades eroding and not making hot section, and a rash of bad BOV's.