Over 80% of indigenous passenger airliners meet ICAO Chapter 2 requirements to noise level. However, out of 23 basic types and their variants that had won certification by 1 July 1997, only nine meet the Chapter 3 requirements. Should the Chapter 3 requirements be introduced in a "smooth" form, three types will be affected, the Tu-154M, Il-62M and Il-96M/T with PW2337 engines. In the case of "tough" form of the Chapter 3 introduction the list will be extended by the Il-96 with PS-90A engines and the Yak-42. ICAO has also begun working out penalties for excessive emission. In the near future ICAO plans to impose a system of limitations and restrictions on using aircraft engines with excessive emission levels. In fact all Russian engines, except for the PS-90A, do not comply with the newly-proposed requirements to NOx emission.