Back to birth traceability (or BtB) is necessary to determine the correct life time of a components. Even though it sounds simple, in many cases creating a BtB trace can be quite challenging and many people struggle with a very clear understanding what a back to birth trace is, how it is established, documented and shown to authorities or aircraft lessees. In this article I will give a quick overview of what BtB actually is and how it is derived from historical documentation.
Why and When is Back to Birth Traceability Required?
To make a long story short – back to birth traceability is needed in case of life limited components (LLP) in order to ensure (and prove, if necessary) that a given component has not yet reached its life limit and is still serviceable. There are not many LLPs on modern aircraft, as the overall tendency is to provide on condition, rather than hard time or life limited, maintenance. Nevertheless, virtually in all aircraft types we will find life limited components particularly in the landing gear, engines and sometimes in the APUs.
A life limit is very important – there are no deviations from manufacturer imposed life limits, and one can assume that a component will fail once the life limit is exceeded. Considering that all LLPs are really crucial aircraft or engine parts (like rotating compressor or turbine disks, for example) you really don’t want them to exceed their life limitations.
Throughout the life of an aircraft, those “major sub-assemblies” (engines, landing gear) are replaced several times. Furthermore, during their shop visits, their components are also being replaced. Due to the fact that the LLPs are often very expensive, it is not uncommon to replace a damaged LLP component with a used one, rather than a new one. Also, the overhaul or repair of such a component may take so long, that it would be unwise to wait with an engine or landing gear overhaul until the repair of the LLP will finish. As a result, an old engine or old shipset of landing gear is likely to contain several LLP components which have been taken from a different unit, operated on different aircraft by different operators and under different authorities.
As you can imagine, making sense of all the documentation and establishing, without any doubt, the actual life consumed of any given LLP may be a tedious job. It is, however, crucial to flight safety and should ever be taken lightly.
The Process of Determining Back to Birth Traceability
Determining the BTB trace of components of new aircraft is very simple, yet I will start with that in order to make the process and the point more clear.
When a factory new aircraft is being delivered to its first operator, it will be accompanied (amongst other documents) with an export certificate of airworthiness and a list of components fitted to the aircraft. This set of documents confirms that all the components fitted to the aircraft at the date of the aircraft’s production are serviceable and freshly manufactured. There may be no release certificates for the components installed on a freshly delivered aircraft (particularly for the landing gear, the engines will normally have a “manufactured” release certificate as they are manufactured by a different company than the aircraft).
The engine and the landing gear log books contain log cards for each life limited component which is part of the master assembly. The log cards are empty, stating only the date of installation of each LLP and the cycles/ hours it had accumulated at installation (normally zero).
So the back to birth traceability for a life limited component fitted to a new aircraft would contain the log card, the release certificate of the master assembly (engine or landing gear leg), the list of parts fitted to the aircraft, showing that the master assembly has been installed at production, and – finally – the export certificate of airworthiness of the aircraft.
Back to Birth Traceability During Operations
As the aircraft is being operated, the master assemblies containing various life limited parts will be replaced and undergo shop visits. During such events, the LLP may be replaced due to damage and wear. Often, to safe costs, airlines may install used life limited parts which have enough life remaining to satisfy the airline’s operational requirements (for example, sufficient life to last to the next planned shop visit of the engine).
After several years of such operation, the master assembly contains few if any of its original life limited parts. More likely, it will become a mix of different parts, some installed new, some originating from other aircraft in the operator’s fleet, and some coming from different operator’s, purchased on the free market. The documentation confirming the back to birth trace will then become complex and needs to be carefully analyzed for completeness and accuracy.
Let’s envision a scenario in which an LLP of an engine is replaced. The operator decides to buy a used components on the market. That component has been used by a different operator on one of their engines, which has been also moved between aircraft throughout its life.
How can we stablish the actual life of the component?
The process is simple, but it is certainly not easy. What we need to do is trace every movement of such LLP component from its manufacture (hence “back to birth”). We can start with the first release certificate the component received fresh from the factory. It’s easy if there is such a certificate. But, as I mentioned, if the component was originally fitted to an engine (and not manufactured as a spare part) it will not have a separate EASA Form One or 8130. Rather, we need the release certificate of that engine and the original listing of components of that engine to confirm that our part was truly installed as “new”. Furthermore, we will need to have confirmation that this engine has been installed on a given aircraft straight from factory. To get this, we will require the export certificate of airworthiness of that aircraft as well as a listing of components originally fitted to it. As you can see, this is already quite a bit of documentation just to confirm when and where the LLP we want to buy has been originally fitted.
Once the “birth” of the LLP has been confirmed, it is necessary to track all movement of the part throughout its life. We need to remember that the purpose of this entire “exercise” is to track all the cycles or flight hours which the given component has made throughout its life. We will deal with three categories of hours/cycles throughout our calculation – the cycles the aircraft has flow while the engine was installed on it, the cycles the engine has flown on different aircraft while the component was installed on it, and the overall cycles of the components. This may become tricky, but that’s why we have the log cards I mentioned earlier. They are designed in a way to make it fairly easy to record all movements of the component. If the previous operator was doing their job right, they will have entered all movements and corresponding cycles on those log cards. All we need to do now is verify their coherence and correctness.
Last but not least, it will be necessary for us to obtain statements from the previous operators confirming that while under their supervision, the engine (or aircraft, or landing gear) to which a given component has been installed has flown a given amount of cycles and has not suffered from any incidents or accidents (I will talk about this in the next section).
All this may be a bit confusing, it takes time and requires to do at least one full BtB trace of a component with a complex history to fully understand the process.
Documents Required to Show Back to Birth Traceability
As always in aviation, no information is meaningful without the proper documentation to support it. This holds especially true for a BTB trace of an LLP component. Below you will find a list of required documentation with a brief explanation why you will need it.
Manufacturer documents start it all. After all, they determine and show the “birth” of the component, with which it’s “life” has begun. There are several manufacture documents which you will need and they may vary from component to component. However, those would be some typical ones:
- Aircraft export certificate of airworthiness together with a fit list of all components installed. This shows that a given component has been installed on the aircraft right after manufacture and was factory new at the time (or not, in which case the number of flown hours and cycles will be shown).
- Master assembly (engine or landing gear) release certificate (EASA Form One, FAA 8130 or equivalent) together with a fit list of sub components fitted at manufacture. This shows that the component has been factory fitted to a new master assembly.
- Release certificate stating “manufactured” for the component itself – you will get this is the component has been manufactured as a spare part, and was not originally installed on any engine or landing gear leg.
Removal / Installation Documentation from Previous Operators
We need to remember that the purpose of the entire BTB process is to accurately determine the number of cycles and/or hours which an LLP component has flown. It is crucial to have installation and removal confirmation for each instance in which the component, as well as its master assembly has been removed from an aircraft and installed on a different one. It is important that such documentation contains the accurate date, flight hours and flight cycles of the aircraft and the master assembly (although sometimes, with enough information, one can be calculated from the other).
Typical documents would include task cards from heavy checks or technical log book entries. In case of task cards, it will be also necessary to have a copy of the CRS of that given check, because the task card itself normally does not constitute a CRS and does not contain the flight hour / flight cycle information. The TLB page, on the contrary, typically contains both.
It will be crucial to have all the shop visit reports for the master assembly, including release certificates, as well as standalone release certificates of the given component if it was repaired or overhauled throughout its lifetime. Some of the information you will obtain in this way may be superfluous, but it never hurts to have a second source of data. If everything has been calculated and recorded correctly, the flight hour and flight cycle information on the shop reports and the release certificates should match the data obtained from the previous operators. If there is no match … well, this will require more digging and, most likely, additional explanation from the previous operators or from the maintenance shops.
Statements from Previous Operators
The BTB will not be complete without a set of statements from the previous operators. There are two kinds of statements and two different reasons for them.
- Statements confirming that the master assembly and/or the aircraft it was fitted to, was flown by the given operator within a given range of dates and for a given number of hours and cycles. This is crucial, as – apart from the flight time information – we need to make sure that the component was always in a controlled environment. If there is a gap between the operators and we don’t know what was happening to the component during that time, the component should be considered scrap.
- So-called non-incident statements. Those statements are mainly necessary for insurance purposes. They confirm that, while the component has been under the previous operator’s supervision, it has not taken part in any accident or serious accident, has not been subjected to salt water or fire, etc. That’s more of a formal requirement, but it is a good thing to have, particularly if the aircraft is leased and will eventually be returned.
The back to birth trace process is difficult and I realize that this article does not cover even all of the basics. However, I hope I was able to give you an idea about what BTB is, why it needs to be done, and what the main difficulties are. It is worth to note that it is typically a good idea to go through that process before a component is purchased. Unfortunately, experience shows that in many cases at the time of purchase there is never enough time for a proper BTB analysis, which sometimes results in a big financial issue if, at a later date, it is determined that one of the required documents is missing and the life of a component cannot be proven without doubt.