A duct connection that does not line up with an RTU curb is not something to force. First verify whether the curb, opening, duct end, or transition is actually off, then document the offset before anyone cuts or adapts the roof connection.
Do not assume the curb is right just because it is installed, and do not field-adapt the opening without approval.
Check
Before assuming the duct is wrong, verify the curb is in the correct location and at the correct elevation. RTU curbs are often set by others and the duct cannot fix a misplaced curb.
Measure the actual curb opening and compare it to the shop drawing, submittal, or approved curb detail. Note size, location, rotation, and elevation differences.
Check whether the duct connection is off in one direction only or whether it is shifted and rotated. That tells you whether a field transition might solve it or whether the layout needs a bigger correction.
Do not cut, enlarge, or field-adapt the curb opening without approval. Curb openings affect roofing, weatherproofing, and equipment fit-up.
Photograph the curb, duct end, and gap with a tape measure in the frame so the offset can be understood without everyone climbing to the roof.
Steps
Before assuming the duct is wrong, verify the curb is in the correct location and at the correct elevation. RTU curbs are often set by others and the duct cannot fix a misplaced curb.
Measure the actual curb opening and compare it to the shop drawing, submittal, or approved curb detail. Note size, location, rotation, and elevation differences.
Check whether the duct connection is off in one direction only or whether it is shifted and rotated. That tells you whether a field transition might solve it or whether the layout needs a bigger correction.
Do not cut, enlarge, or field-adapt the curb opening without approval. Curb openings affect roofing, weatherproofing, and equipment fit-up.
Photograph the curb, duct end, and gap with a tape measure in the frame so the offset can be understood without everyone climbing to the roof.
Say this to your foreman
The duct connection does not line up with the RTU curb at [location/unit tag]. The offset looks like approximately [size/direction]. Do you want me to hold and document, or is there an approved field transition I should use?