Question on Passenger to Freight Conversion

[sirbrandon]

I have some questions regarding these type of modification works. I am an aeronautical engineer by training, but not practicing. I know some aircraft design theory and stuff, but I do not have experience with what actually goes on in the shops. I would like to know more about what goes on when an aircraft is put on one such PTF program. What are some of the things that are done to the aircraft with regards to the main airframe structure? These kind of work, I would presume, would involve some CAD designing and probably analysis to determine the safety factors. Are maintenance engineers involve in such work or would these by the domain of aerospace/aeronautical engineers?

 

[rb1957]

of course there are structural changes ... an enlarged cargo door, an upgraded floor, a payload handling system, revised (cheapened, toughened) interior, but the "fun" stuff are lots of technical issues ...
flammablity and new firex systems
connection into the aircraft ICAS system (like for new door warnings, new fire alarms, ...)
maybe decompression (if you're opening up the cabin, or if you're dividing it)
...

another day in paradise, or is paradise one day closer ?

 

[LiftDivergence]

In terms of the airframe, naturally the largest changes occur around the main cargo door. But the structural additions / reinforcements, etc. can have and effect on the aircraft which is more far reaching.

Typically the design work, new drawings, and the like is all completed by engineers working for a company that specializes in this type of thing (think Precision Connversions, IAI, etc.), who apply for an STC. Some MROs specialize in performing conversions.

As part of the STC they must supplement the OEM SRM, SSID, DTR Check forms...the whole lot. For each conversion there will be an explicit affected area diagram or some kind of published FCAS (fatigue critical alteration structure). All these documents would better answer your question if you could find a copy for some STC.

Each converted aircraft will have adjusted inspection requirements in the maintenance program in accordance with the STC supplements due to altered loading and stress.

As you can imagine, often times older airframes receive the conversion. There are usually existing repairs with inspection requirements which interfere with the STC installation in some way. The most interesting part of cargo conversions to me is the damage tolerance aspects of the newly configured airframe. It can be a little bit of a DT and compliance hassle. This also goes for new repairs common to an installed cargo mod plane.

Basically, if you ever work a repair on a modded airframe, make certain you review all the STC documentation to determine exactly what you are affecting.

Keep em' Flying
//Fight Corrosion!

 

[verymadmac]

in addition to LiftDivergence's comments,

I have found freighters are a hell of a lot more fun than passenger aircraft to support. I have only worked supporting freight operations but determining airframe loads and the like was a regular exercise (but our aircraft were the cheapest airframes a converted by the cheapest conversion house, so always broken, always in need of improvements).

All the passenger related kit is removed, electrical (if you are lucky they take it back the CB panels, if not they cut it at some random place and cap and stow), galleys , lavs (there is typically one lav, some stowage space and seating for supernumerary's installed). The air conditioning is also typically modified (different cabin requirements and smoke control).

They often reinforce the floor beams. Cabin Windows are blanked. The main deck hold is lined with cargo liner, and fitted with lights and smoke detectors. Often there is a rigid 9G bulkhead install at the front of pallet position 1. Additional lights, etc may be required for supernumerary in-flight access into the hold. There are new paths for airflow in the cause of blow outs, so blow out panels and vents need to be installed (we had aircraft that operated in the tropics, where the blow out panels was not water proof, next to the door (L1) used for access and over the inertia nav units, which regularly let the smoke out due to getting wet).

There is no legal scope for passengers in FAR25 on on Class E freighters, so any person not flight crew that is carried is, as a supernumerary, it is defied by exemptions what associated equipment etc is required (they are either associated with the freight or are company employees, no paying punters). So there are more lights, bells and buzzers installed to support their carriage.

The associated fire suppression methods means there is a requirement for continuous O2 for all POB for the extent of its ETOPS range. So more O2 capacity as well as outlets.

Where items are installed becomes driven by product change rule as well, it appears that supernumerary seats on a 9G barrier must meet the amendment status of the barrier (so dynamic) but if they are on original airframe structure non dynamic.

There are lots of interesting exemptions relating to freighter on the FAA exemption search engine, the IAI's are the first one I tend to read (most comprehensive and useful).

Depending on the conversion shop they also add lots of extra features like non round holes, fudged inspections, bags and bags of FOD behind panels.

 

[sirbrandon]

Thanks for all the replies. Much appreciated.

Looks to me the PTF process is a lot more complicated than the usual maintenance checks, more like a re-design process with the final goal of getting the STC. This is interesting to me as I am trying to understand how aerospace companies are categorized based on the type of business activities that they undertake. I presume a company that does PTF will typically be also involved with MRO, but probably not vice versa?

I'm also trying to understand what "Aerospace manufacturing" encompasses. I have spoken to some people who claim that manufacturing companies must strictly adhere to the Part 21 certification to be considered as "aerospace manufacturing". If a Tier 2 company makes parts for both landing gears as well as domestic dishwashers (for example...) and is not Part 21 certified, but it supplies these parts to a certified Tier 1 company, can it be considered as an "Aerospace Manufacturer"? What do you guys think?