FAR 21.97 — Major Type Design Changes

FAR 21.97 sets the requirements an applicant must meet when seeking FAA approval of a major change in type design. A type design defines the certificated configuration of an aircraft, engine, or propeller, so any major change to it must be formally approved before the product can be produced or operated under that certificate.

To get approval, the applicant must:

• Provide substantiating data and the descriptive data needed to incorporate the change into the type design.
• Show that the change and any affected areas comply with the applicable airworthiness requirements of this subchapter, and give the FAA the means used to demonstrate that compliance.
• Submit a statement certifying compliance with the applicable requirements.

For aircraft engines, the approval applies only to the specific engine configuration that was changed — unless the applicant identifies other configurations of the same engine type in the descriptive data and shows the change is compatible with those configurations. This matters operationally because it ensures modifications don't compromise certificated safety standards across an engine family.