Replicating the effects of tailrotor failure during flight test or pilot training is so dangerous that there is a shortage of data on how to deal with it, says an extensive UK Civil Aviation Authority study. The analysis suggests measures - including a retrofittable inflatable drag chute - that could be deployed to counteract the spin normally resulting from tailrotor failure.

The dangers associated with gathering data on tailrotor failure means manufacturers neglect possible design measures that might mitigate its effects. In addition, data has not been gathered to enable accurate simulation, and pilot training is neglected, says the CAA.

In 50% of cases, tailrotor failure occurs because the rotor strikes an object, and in 30% tailrotor drive failure occurs. The failure can take various forms including blade damage or separation, failure of the pitch control mechanism, or tailrotor drive failure, and the results of this vary. The effect on the aircraft is a tendency at least to yaw and usually for the yaw to develop into a spin, making an immediate reduction of power to the main rotor essential, committing the aircraft to immediate height loss.

The CAA says that most training schools do not demonstrate tailrotor failures or discuss it and manufacturers do not conduct sufficient analysis of possible effects, leading to a shortage of advice in type operation manuals on how to handle a tailrotor failure. The CAA says that this neglect must change.

Six-axis motion full-flight simulators are the only potential method of teaching and researching the operational and training aspects of tailrotor failure, but the data has to be derived to make the simulation realistic, says the report.

In the meantime, drag chutes would increase control in the event of tailrotor failure, and the CAA says that more data might be extracted from health and usage monitoring systems to reduce the incidence of tailrotor malfunction.

Source: Flight International