I found sumfin...:
The text of Annex 16 describing the maximum noise levels for the new Chapter 4 noise limit is as follows:
• The maximum permitted noise levels are defined in Chapter 3 of Annex 16; and may not be exceeded at any of the measurement points;
and
• The sum of the differences at all three measurement points between the maximum noise levels and the maximum permitted noise levels (the Stage 4 limit) specified in Chapter 3 of Annex 16 may not be less than 10 EPNdB; and
• The sum of the differences at any two measurement points between the maximum noise levels and the corresponding maximum permitted noise levels specified in Chapter 3 of Annex 16 may not be less than 2 EPNdB.
(1) None of an airplane's maximum noise levels (flyover, lateral, and approach) may be greater than the maximum permitted noise levels for Chapter 3 airplanes, as defined in Annex 16; and
(2) To determine Stage 4 compliance, an airplane's maximum flyover, lateral and approach noise levels are each subtracted from the maximum permitted noise levels. The differences obtained are the noise limit margins, to be used as follows:
(a) When the three margins are added together, the total must be 10 EPNdB or greater; and
(b) When any two of the margins are added together, the sum must be 2 EPNdB or greater.
For the 680 its easy too see that it is stage 4....the sum for lateral, flyover and approach noise levels is 281dB...the Sovereign emits 250,4, the smallest difference being 6,4 for lateral noise ( 87,6 vs. 94 dB )