Just looking at the certified levels is not enough to judge if a particular aircraft has enough margin to be certified to Chapter 4. There is a list of 12 questions the recertifier must be able to answer appropriately for each question. If the Chapter 3 certification was done using methods that are no longer acceptable than another test must be conducted. The difference in the methods used to certify could cause the noise levels to go up enough to flunk Chapter 4.
