Before revision: Use of testbed aircraft Ilyushin Il-76LL testbed aeroplane with experimental TV7-117ST engine Yak-40-based testbed aircraft with a hybrid transmission For example, in development of new aircraft engines, these are fitted to a testbed aircraft for flight testing, before certification.
After revision: Use of testbed aircraft McDonnell Douglas MD-81 testbed with experimental GE36 propfan engine Yak-40-based testbed aircraft with a hybrid transmission For example, in development of new aircraft engines, these are fitted to a testbed aircraft for flight testing, before certification.