40 CFR 87.23: Exhaust emission standards for Tier 6 and Tier 8 engines.

Exhaust emission standards apply to new aircraft engines as follows:

(a) New turboprop aircraft engine standards apply as described in 40 CFR 1031.40.

(b) New supersonic engine standards apply as described in 40 CFR 1031.90.

(c) New subsonic turbofan or turbojet aircraft engine standards apply as follows:

(1) Standards for engines with rated output at or below 26.7 kN thrust apply as described in 40 CFR 1031.50.

(2) Standards for engines with rated output above 26.7 kN thrust apply as described in 40 CFR 1031.60.

(d) NOX standards apply based on the schedule for new type and in-production aircraft engines as described in 40 CFR 1031.60.