Star formation primarily occurs in filaments where magnetic fields are expected to be dynamically important. The largest and densest filaments trace spiral structure within galaxies. Over a dozen of these dense (∼10 4 cm −3 ) and long (>10 pc) filaments have been found within the Milky Way, and they are often referred to as "bones." Until now, none of these bones have had their magnetic field resolved and mapped in their entirety. We introduce the SOFIA legacy project FIELDMAPS which has begun mapping ∼10 of these Milky Way bones using the HAWC+ instrument at 214 µm and 18. 2 resolution. Here we present a first result from this survey on the ∼60 pc long bone G47. Contrary to some studies of dense filaments in the Galactic plane, we find that the magnetic field is often not perpendicular to the spine (i.e., the center-line of the bone). Fields tend to be perpendicular in the densest areas of active star formation and more parallel or random in other areas. The average field is neither parallel or perpendicular to the Galactic plane nor the bone. The magnetic field strengths along the spine typically vary from ∼20 to ∼100 µG. Magnetic fields tend to be strong enough to suppress collapse along much of the bone, but for areas that are most active in star formation, the fields are notably less able to resist gravitational collapse. * Hubble Fellow are used to trace spiral structure within the Milky Way (e.g,. Reid et al. 2014). Observations from Spitzer revealed that some of these star-forming clouds are dense (∼10 4 cm −3 ), high-mass, and exceptionally elongated (e.g., over 80 pc × 0.5 pc for the Nessie filament; Jackson et al. 2010;Goodman et al. 2014). These filamentary structures are called bones because they delineate the