Works related to identification of harmful exhaust components from aviation engines have continued since the second half of the last century. These works focus on high-thrust turbine engines. For this, group testing and standardization procedures have been developed containing the admissible limits of exhaust components. Since 2007 works have been underway related to the identification of harmful exhaust components from engines of low power output that have not yet been included in the emissions legislation. These actions are particularly related to the measurements of the exhaust emissions from piston aviation engines and they are focused on the fuel applied for these engines. This book presents the results of the author's own research work related to the issues of exhaust emissions from powertrains of aircraft and helicopters fitted with piston or turbine engines not yet included in the emission legislation. Research has been presented for turbocharged piston and jet engines aircraft. Test procedures have been presented related to the measurement of the exhaust emission under actual conditions of operation. The study presents analyses of the operating conditions of aviation engines, for which data from the on-board recording devices (flight parameters) have been used. Tests have been developed related to the engines operating under actual operating (in-flight) conditions. The methodology of the developed test has been validated based on a test dedicated for an aircraft fitted with a jet engine. The test results have been subject to a comparison with the results of tests applicable in the homologation procedures. Eventually, the authors proposed exhaust emissions tests dedicated to individual aircraft groups.