TCAS II Training
TCAS II has shown itself to be reliable, especially when compatible RAs have been posted: by this I mean when two aeroplanes are converging and the TCAS in one posts 'Climb', the other will post 'Descend'.
What is highly important is that both crews have been trained never to manoeuvre against the sense of the RA that their TCAS posts. In the situation I have described, if my TCAS has posted 'Descend' I should descend, but if I stay level (assuming that is where I was), the other aircraft - by climbing - will still establish sufficient vertical clearance to avoid a collision. Only if I go against the sense and climb will I negate the benefit TCAS is attempting to deliver.
Pilots of UK-registered aeroplanes that have TCAS II would, before the JAA TGL No 11 was published, have been trained according to CAP 579, in which paragraph 6.2.4 states:
Manoeuvres should never be made in a direction opposite to that given in an RA: this is because the sense may have been determined following an exchange of data with the established threat. For this reason:
(a) RAs may be disregarded only when pilots visually identify the potentially conflicting traffic and decide that no deviation from the current flight path is needed.
(b) If pilots receive simultaneously an instruction to manoeuvre from ATC and an RA, and both conflict, the advice given by ACAS (aka TCAS) should be followed.
After TGL No 11 was published, pilots of aeroplanes operated under an air operator certificate based upon JAR-OPS 1 should have received the training this TGL contains. A Note on page 11-8 states:
If a decision is made not to follow an RA, no changes to the existing speed must be made in a direction opposite to the sense of the displayed RA. Pilots should be aware that if the intruder is also ACAS equipped, the decision not to follow an RA may result in a descrease in separation at CPA (closest point of approach) because of the intruder's RA response.
And a note on page 11-9 states:
If pilots simultaneously receive instructions to manoeuvre from ATC and an RA which are in conflict, the pilot should follow the RA.
JAA TGL No 11 was based upon ICAO guidelines and so should represent an international standard that all operators could follow.