Refer to figure.
EASA learning objective 022.12.10.01.08 states: “State that ACAS II equipment can take into account several threats simultaneously.”
Eurocontrol ACAS II Guide dated March 22 states: 'ACAS II is able to handle multi-threat encounters either by attempting to resolve the situation with a single RA (i.e. pass above all threat aircraft or pass below all threat aircraft) which will maintain safe vertical distance from each of the threat aircraft, or by selecting an RA that is a composite of non-contradictory climb and descend restrictions (i.e. requiring own aircraft to pass below some aircraft and pass above others). '

TCAS II can monitor as many as 45 aircraft, display up to 30 of them and can coordinate a resolution advisory (RA) for up to 3 threats simultaneously.

To generate an RA the conflicting aircraft must carry a Mode C or S transponder. An RA is represented on a pilots navigation display (ND) or electronic VSI (EVSI) as a solid red square with relative altitude and vertical motion shown by a small arrow to the right of the symbol when it exceeds 500 ft/min.

TCAS II handles multi threat encounters by attempting to resolve the situation with a single RA (i.e. pass above or below all threats) or by selecting an RA that's a mixture of non contradictory climb and descent commands. (pass below some threats and above others). Therefore the vertical manoeuvre commands given take into account more than one conflicting aircraft at the same time.

In the multi threat example in the figure the TCAS would give the aural annunciation 'Level off, level off' and the pilot should aim to put the VSI needle in the green band avoiding the red pitch angle areas on the PFD.

This question is problematic as the ambiguous wording of the answers and the lack of definitve feedback means that we have had to choose the most technically correct statement as the correct answer. If you encounter this question in your exam with a different answer then please let us know.

It is capable of providing you with information on the 3 aircraft, but only an RA for one aircraft at a time --> INCORRECT. Yes it will give a single RA for the aircraft that is the highest threat BUT the vertical manoeuvres will take into account the other conflicting aircraft, therefore the statement '.... one aircraft at a time' isn't true.

It is capable of providing you with vertical manoeuvres for the 3 aircraft at the same time --> CORRECT. The vertical manoeuvres commanded by the single RA will take into account the altitudes ot the other conflicting aircraft to avoid the domino effect of avoiding one aircraft only to collide with another!

It is capable of detecting potential conflicts with the 3 aircraft and providing advisory alerts --> INCORRECT. It provides a Resolution Advisory (RA) not 'advisory alerts'.

It is capable of suggesting resolutions to avoid potential collisions with the 3 aircraft --> INCORRECT. RA's aren't suggestions they're commands.