What we have been informed

• In order to reduce the risk of Airborne Collision Avoidance System (ACAS)/TCAS Resolution Advisories (RAs) which are subsequently shown to have been operationally unnecessary - so called “nuisance” RAs - many operators have standard operating procedures requiring the pilots to reduce rate of climb/descent to less than 1500 ft/min when in Reduced Vertical Separation Minima (RVSM) airspace or within the last 1000 ft before cleared level;
• Some operators have expressed concern that when ATC controllers specify a rate of climb or descent, they expect the pilots to maintain the given rate until intercepting altitude;

What are the facts and rules?

RAs could occur when aircraft are in close proximity and the vertical speed of closure, which may be the sum of the vertical speeds of both aircraft or the vertical speed of just one aircraft, exceeds 1500 ft/min;

• Flight Crews can reduce the likelihood of an RA by confining vertical speeds to less than 1000 ft/min, and ideally between 500 and 1000 ft/min, within the last 1000 ft before reaching assigned level. Many national authorities have issued recommendations to this effect within their flight rules and procedures;
• ATC may request different rates of climb or descent at any time for the purpose of maintaining separation of aircraft. In such cases, these rates shall be strictly complied with. Failure to do so could result in a potentially serious loss of separation. It should not be supposed that there will 'automatically' be an RA;

What are the potential solutions?

Aircraft Operators

• Remind flight crews that, if able, they are expected to comply with ATC instructions regarding rates of climb and descent.

ANSPs

• Remind controllers of the possibility of “nuisance” RAs when vertical speeds exceed 1500 ft/min when approaching a cleared level and there are other aircraft in close proximity. (1500ft/min in itself does not mean that there will be an RA - it depends whether there are other aircraft in close proximity.)

Disclaimer

© European Organisation for Safety of Air Navigation (EUROCONTROL) October 2005. This alert is published by EUROCONTROL for information purposes. It may be copied in whole or in part, provided that EUROCONTROL is mentioned as the source and to the extent justified by the non-commercial use (not for sale). The information in this document may not be modified without prior written permission from EUROCONTROL. The use of the document is at the user’s sole risk and responsibility. EUROCONTROL expressly disclaim any and all warranties with respect to any content within the alert, express or implied.