Selecting aircraft lumber is both an art and a science. It all begins with a visual inspection of a piece of lumber that holds ‘a promise’. It takes an experienced eye to know the difference between ‘probably aircraft grade’ and ‘close, but no cigar’. Visual inspection is therefore not only a part of the official norms, referencing to things like grain runout, annual ring spacing and a lack of defects, but also an intuitive process of selection preceding the actual testing to defined norms. It takes many years of handling lumber to develop the proper skills.

Lumber is a product of nature. It is inherently subject to wide variations in quality, differing in things like density, annual ring spacing, modulus of elasticity, brittleness and specific strength. Over the years, governing institutions in many countries have defined norms to manage the testing and use of lumber in aircraft construction. In order to assure that the lumber employed in an aircraft structure meets these requirements, it is important to manage the entire chain of custody.

Our sawmill in Northern Canada keeps track of each individual board sawn from a log. During the sawing process each board is marked with a code related to the log ID number. This is a requirement for wood used in aircraft under the French NFL-17-966. It also makes sense, because it enables us to supply spars with almost identical bending characteristics. This method of tracking and tracing each log and it’s technical characteristics also supports our in-house research programs. Finding top quality Sitka spruce suitable for use in aircraft and meeting the MIL-S-6073 (US), BL6 (UK) and NFL-17-966 (France) is becoming increasingly difficult. The chain of custody linked to our testing lab is vital to identify the best regions to source aircraft grade Sitka spruce.

The in-house wood testing laboratory.
At our mill in Holland we have a unique wood testing laboratory in-house. We are the only mill in Europe equipped to determine axial compressive strength, impact strength, tensile strength, 3-point bending, brittleness and dry-weight. Most testing equipment is built by the famed Galdabini company and all key functions feature modern electronics.

Please note that we do not certify aircraft lumber, we merely select and verify to ensure that the wood supplied will pass the criteria set by the certifying bodies. Of course final testing and the decision to actually use a piece of wood lies with the builder, however should a piece of lumber delivered not meet required norms, Touchwood will replace it.