Type Certificate Question


GhostRider in the Sky
I may have asked this question before, but to what extent can an airframer, ie Boeing, modify an existing type, via improvements, within the scope of a current type certificate?

Example, I just read an article that mentioned that the 737NGs rolling off of the assembly line today are much better performers than when the type was initially introduced. I know that they put new wing fairings on updated versions of 747s, and I know they make continuous improvements aerodynamic improvements on the 737 series.

I've also seem pictures of Gulfstream GIIs with different nose-cone profiles.

So to what extent, and on what structures, can the manufacturer make modifications under the current Type Cert?

Thank you in advance.


All the responsibility none of the authority
That's a great question, and to be honest I'm not entirely sure.

Right now, the parent company is getting set for the 747-8 (it's -8, not a -800 Okay?).

Boeing wants to certify the plane as a deriviative of the 747-400, which is a different TC than a 747 classic (-100/-200/-300), instead of an entirely new TC.

So they are wrangling with the feds right now. The -8 will have a differently configured wing (think 767-400 wingtips instead of the winglets) and a, for lack of a better term, different avionics package. I mention these because they can affect the handling qualties of the aircraft and, at an operational level, the functionality of the basic fundamentals of avionics operation.

I'm not sure as far as actual structure or materials are concerened, nor any design changes, how they may affect the decision to make it a derivative or new TC.


GhostRider in the Sky
I did a quick google search and came up with this from Wikipedia (which I always take with a grain of salt, and research the internal documentation to establish validity)

Changes to type certificate

Often the basic design is enhanced further by the type certificate holder. Major changes beyond the authority of the service bulletins require amendments to the type certificate. For example, increasing (or decreasing) an aircraft's flight performance, range and load carrying capacity by altering its systems, fuselage, wings or engines resulting in a new variant may require re-certification. Again the basic process of type certifications is repeated (including maintenance programs). However, unaltered items from the basic design need not be retested. Normally, one or two of the original prototype fleet are remanufactured to the new proposed design. As long as the new design does not deviate too much from the original, static airframes do not need to be built. The resultant new prototypes are again subjected to flight tests.
Upon successful completion of the certification program, the original type certificate is amended to include the new variant (normally denoted by a new model number additional to the original type designation). Typical examples are; the Boeing 737NG (737-600, 737-700, 737-800 and 737-900) which replaced the 737 Classic family (737-100, 737-200, 737-300, 737-400 and 737-500) and the Airbus A340-500 and the A340-600 which is based on the Airbus A340-200 and the A340-300.