Originally Posted by
tdracer
Duck
After the Helderberg disaster, the regulations governing "Combi" aircraft were significantly changed. While out of my area of expertise, those who are in the know have told me it would be close to impossible to certify a new Combi style aircraft to the updated regulations.
All the Combi's currently in operation where certified prior to the regulations being updated in response to the Helderberg.
As DR notes, military operations do not need to comply with commercial certification restrictions.
I recognize I'm continuing a major thread drift, but this information may be of interest to some:
TD - It wouldn't be impossible - just more costly. The main deck cargo compartments on the various combi jet transports produced in past decades were Class B compartments as defined in 14 CFR 25.857 at the time. Class B compartments are required to have fire /smoke detection, but are not required to have built in fire extinguishing/suppression. The change in the definition of a Class B cargo compartments in the rule effective in 2016 went from one where the crew had to have adequate access to enter the compartment and fight a fire to now requiring the crew to be able to effectively fight any fire in the compartment with a handheld fire extinguisher from one access location without entering the compartment. This has the effect of severely limiting the size of compartments that can meet the Class B definition relative to the old definition. "Combi" large main deck cargo compartments on passenger airplanes as previously designed typically were much too large to meet that new requirement, forcing any such compartment on a new airplane to be classified as a Class C cargo compartment like the lower deck compartments, which requires an extinguishing (suppression) system.
So it's not impossible to obtain a type certificate for a combi today, but it's apparently not cost effective to design, certificate, build, and operate a combi compared to running cargo separately on all-cargo airplanes that have less costly fire safety requirements, as evidenced by combis not being proposed in recent years.
Changes were required by AD after the 1987 South African Airways 747-200 Combi accident prior to this rule change, but this 2016 change was one of the eventual part 25 changes that resulted from that accident. The FAA lessons learned library has an extensive section on this accident and the various actions that resulted. Here's a link to it:
https://lessonslearned.faa.gov/ll_ma...abID=1&LLID=33