"Choosing the right advice" (Flight International, 5-11 August) can only be done if you have the right knowledge. David Connolly seems to lack essential information and draws the wrong conclusion.

An aircraft "at the top of its altitude envelope" has, according to certification requirements, still a speed margin of 30% above stalling speed (1.3Vs). Traffic alert and collision avoidance (TCAS) was designed to use this margin down to 1.2Vs "in reasonable severe conditions" (eg "climb" resolution advisory [RA]" at maximum altitude) and close to stalling speed (Vs) "in reasonable worst case conditions" (eg "increase climb" RA). A well- trained pilot should therefore not have any problem in following an RA. And he/she would also know that stall (as well as ground proximity) warnings would always override an RA.

To ignore an RA ("do nothing and wait for the intruder to react") or unnecessarily selecting traffic advisory only would be a dangerous abandonment of a safety device that has been effective many times.

Eurocontrol is right to urge all pilots to rely on the most accurate device. The onus is on national authorities to ensure that all pilots fully understand the design philosophy of TCAS and have sufficient experience in hand-flying all manoeuvres in the most critical situations. Last year's accident and several near-collisions have tragically shown that there are more deficiencies in safety management than in TCAS equipment and software.

Heinz Fruehwirth Vienna, Austria

Source: Flight International