This SAE Aerospace Recommended Practice (ARP) standardizes test equipment and procedures for the measurement of smoke emission from aircraft gas turbine engines. The procedures included are for determining and reporting the amount of smoke emission. Tests have indicated that the practically achievable precision of the smoke number is within ±3 when the system is properly used as outlined herein. This procedure is not intended for in-flight testing, nor does it apply to engines operating in the afterburning mode.