Wanted: reliable low-speed indicator

 - March 30, 2009, 6:24 AM

The European Aviation Safety Agency (EASA) is continuing its search for a lightweight and affordable low-speed indication and warning device for use in the civil helicopter market. The agency launched the tender in October, citing the need for accurate speed measurement and the poor performance of current pitot tubes.

According to project certification manager Ricardo Frollo, a device that provides a low-speed indication from all directions would be ideal. This would include associated warning, when necessary. Existing systems are for military or research use only and thus are not tailored to the civil market, he said. The EASA will not fund the development of the selected design, however, as it is not in its remit, a spokesperson told AIN.

The current pitot systems, which use differential air pressure, do not provide an accurate measurement a low speeds. According to Frollo, a pitot tube can measure forward speeds above 35 knots, but a great part of a helicopter’s flight envelope falls outside this range. Yet, in flight manuals, it is commonplace to find limitations, such as “sideward flight has been demonstrated up to 20 knots” and flight with “both sliding crew doors fully open and secured is limited to 27 knots indicated airspeed.” But pilots can only estimate these speeds because existing civil pitot systems cannot provide an accurate indication if airspeed is low or the helicopter is flying sideways or backwards.