waveguide from which the PCC is formed is far from the light-line $\omega~=~ck_{x}$, where $k_x$ is component of the wavevector $k$ parallel to the PCC’s waveguiding axis [@PCbook]. Lowering the bandedge frequency from which the PCC mode is formed, either by increasing the effective refractive index $n_{eff}$ or basing a PCC on a dielectric mode, reduces coupling between the optical mode and radiation modes above the light-line, and thus reduces loss. Dielectric mode Si$_{3}$N$_{4}$ PCC’s have been shown to have high $Q_o$ [@Khan:11], have been demonstrated in the resolved-sideband regime of cavity optomechanics [@Davanco:14], and have been used to study the emission properties of SiN [@Barth:08] and to modify spontaneous emission [@Barth:07]. Dielectric mode zipper cavities have also been used for cavity optomechanics [@Eichenfield:09], and side-coupled optical and mechanical beams can form slot-mode optomechanical crystals that have been used in multimode optomechanics [@Grutter:15]. These devices are often designed at target wavelengths for specific applications, for instance at 637 nm for interfacing with diamond color centres [@McCutcheon:08].

In contrast, free-standing air-mode Si$_{3}$N$_{4}$ PCC’s at telecommunication wavelengths have not been reported to the best of the authors’ knowledge. Here we show that air-mode Si$_{3}$N$_{4}$ nanobeam PCC’s based on tapered round holes can 