Recent letters from Anthony Mullard (Flight International, 17-23 June) and Eric Walmsley (10-16 June) on the pros and cons of using approved parts manufacturer (PMA) parts make interesting reading.

In my experience of 50 years working for two original equipment (OEM) aircraft wheel and brake manufacturers in the UK and USA, and now with a PMA aircraft brake replacement parts manufacturer, I have found that it is a misunderstanding to believe that PMA parts are inferior to and not tested and certificated to the same levels as the OEM parts.

To obtain approval by the US Federal Aviation Administration to produce parts to the PMA process and obtain a supplemental type certificate (STC) from the FAA requires the satisfactory completion of a detailed test programme that not only requires laboratory and dynamometer testing but also, in the case of aircraft brakes, on-the-aircraft runway testing. As the FAA issues the original aircraft type certificate it must be in the best position to determine whether or not PMA parts satisfactorily meet the required criteria.

In the past, non-certificated maintenance and overhaul parts, commonly known as "bogus parts", have infiltrated the aircraft industry. Any experience with these parts should not be compared with the performance of genuine FAA PMA and STC-approved products.

In efforts to contain costs and maintain competition within the aircraft industry, the PMA parts industry plays a very valuable role.

Terence Jones San Marcos, Texas, USA

Source: Flight International