27 September 2007
FR Doc E7-19053
Federal Aviation Administration (FAA)

The Bell Augusta BA609 tiltrotor is a smaller civilian version of the military’s V-22 tiltrotor. The notice requests comment on proposed standards for certifying the BA609. The tiltrotor is designed to take off and land like a helicopter, rotate its engines, and cruise like a conventional turboprop airplane. The FAA does not have standards for an aircraft with this unique design feature; the tiltrotor is referred to as a “special class” category of non-conventional aircraft. The FAA has put together 105 pages of airworthiness standards for which it is seeking comment.

Those standards are not included in the notice, but may be accessed at www.faa.gov/aircraft/draft_docs/ Those standards do not appear to address vortex ring state, when the airplane is descending for landing in the helicopter mode and flies into its downwash, causing a loss of lift. If this condition occurs asymmetrically (e.g., on one side or the other) the aircraft can flip over in flight. However, the draft standards do state:

“Control of engines, thrust producing devices, and conversion devices which may affect or are intended for aircraft stability and control must regulate the magnitude and rate of control of power as required for compliance with [and here lists a whole variety of existing airworthiness standards].”

And,

“The approach and landing must not require exceptional piloting skill or exceptionally favorable conditions, and the landing must be made without excessive vertical acceleration or tendency to bounce, nose over, ground loop, porpoise, or water loop.”