Engine manufacturers have only themselves to blame for the parts manufacturing approval (PMA) threat. PMA replacement parts became established in the first place because customers were unhappy with the cost and availability of original equipment manufacturer (OEM) spares, particularly for out-of-production types.
Parts manufacturing approval is intended to guarantee 'identicality' - that PMA parts are identical in form, fit and function to OEM components. To persuade airlines to buy their parts, many PMA manufacturers offer (or at least claim to offer) higher quality parts than the OEM original - usually in terms of longer life.
But the biggest reason for their popularity remains their cost - typically 20-30% lower, but often up to 50% lower than OEM parts - and availability, with delivery in days instead of weeks.
Reassured by the rigour of the PMA process, and attracted by cost, availability and quality benefits, major airlines have gone from insisting on OEM-only parts to actively seeking PMA ones. The majority are non-safety-critical airframe parts, but an increasing number are flight-critical engine parts, such as blades and vanes.
Engines can cost billions to develop, but this is seldom reflected in the price paid by airlines. Instead, manufacturers aim to recover their investment on through-life support, investing heavily in engine services subsidiaries to capture the aftermarket business they once ignored.
On one level, the OEMs' concerns are valid. As more PMA parts are used in engines, the chances of an accident caused by a PMA part increase. They argue that, because PMA manufacturers do not have access to the OEM's proprietary data, they cannot guarantee that the part they are supplying is identical to the original, and equally safe.
There is a precedent here - the GATXAirlog 747 freighter conversion supplemental type certificate (STC). In a similar way to a PMA, an STC requires the non-OEM to prove that the conversion is at least as safe as the original, usually without access to original design data. Airlog designed its 747 cargo door modification using publicly available Boeing loads data, which was later found to be faulty. Cracks developed and the FAA required that GATX revalidate the conversion. The result is that fundamental changes are being made to the data requirements for STCs which favour OEMs.
PMAs get their data in various ways. Some literally reverse-engineer the OEM part. If the engine was originally developed for the US military, the data is publicly available. Manufacturers have even accused PMAs of making unauthorised use of OEM data obtained via operators.
Maintenance companies, meanwhile, are not supposed to use PMA parts without customer approval. Major airlines feel comfortable using PMA parts because they use their own engineering staff to do the quality checks. Where there could be grounds for concern is with less technically capable airlines or those which outsource their maintenance to reduce costs.
But barring events that could reverse the growing popularity of PMA parts, they are here to stay. Instead of stirring up safety concerns, engine manufacturers would do better to look at the root cause of their increasing popularity - the cost and availability of spares. While engine developers have to be able recover their substantial investment to stay in business, high spares prices are counterproductive.
The best weapon the OEMs have is not scare tactics but the cost savings that through-life maintenance deals such as power-by-the-hour give. These offer airlines predictable maintenance costs and the ability to reduce or eliminate investment in non-core activity. They also offer OEMs predictable service revenues and control of the engine, its data and the customer's loyalty.
The PMA industry must be regulated closely - the temptation to cut corners to lower costs is great and preventing shortcuts around the already costly PMA process should serve to deter the slipshod or unscrupulous. But in the end, only by reducing the cost and improving the experience of owning their engines will the OEMs hold on to a market they consider theirs by design right.
Source: Flight International
