Module 2 - ATM - ACAS and Ground Based Safety Nets Flashcards
What is the difference between ACAS and TCAS?
ACAS refers to the standard or concept whereas TCAS refers to the implementation. Although the terms are used interchangeably.
NB: TCAS II is the only implementation that meets the ACAS ICAO SARPs.
What does ACAS II/TCAS II do/How does it work?
- Works independently of the ACFTs navigation equipment and ground systems used for the provision of air traffic services. Based on time to collision, allows pilot to identify conflicting traffic and take avoiding action if necessary.
- Can track up to 30 ACFT within 14NM for Mode A/C and 30NM for Mode S.
- Onboard equipment reacts to the transponders of ACFT to determine whether or not there is a potential risk of collision.
- Provides Traffic Advisories (TAs) to help pilots see intruders and Resolution Advisories (RAs) which are recommendations to the pilot to carry out a specific avoidance manoeuvre.
Cockpit presentation of traffic display for ACAS/TCAS:
- ) How is own ACFT represented?
- ) How is other traffic with unknown altitude represented?
- ) How is proximate traffic represented?
- ) How are traffic advisories represented?
- ) How are resolution advisories represented?
- ) Airplane symbol in white or cyan.
- ) Unfilled diamond in white or cyan.
- ) Filled diamond in white or cyan.
- ) Filled yellow/amber circle.
- ) Filled red square.
Describe a Traffic Advisory (TA) and cockpit actions.
- Typically given 45 seconds before assumed collision.
- Pilots are advised not to take avoiding action based on a TA alone and may ask for traffic information.
- Pilot looks for conflicting ACFT visually and does not manoeuvre.
NB: May be issued of the conflicting ACFT is not reporting altitude.
Describe a Resolution Advisory (RA) and cockpit actions.
- Typically given 30 seconds before assumed collision.
- Pilot receives advise to climb, descend or maintain current level. Rate of climb or descent may also be given. Pilot is expected to respond immediately in accordance with the RA.
- Manoeuvres to be restricted to minimum necessary to avoid conflict.
- Pilot to advise ATC unit as soon as possible thereafter.
- Return to original flight path as soon as it is safe to do so.
- TCAS II designed to take host ACFTs performance characteristics and level into account when issuing RA.
NB: Will only be presented if the conflicting ACFT is using Mode C or S. If both ACFT fitted with TCAS II, transponders communicate and complementary RAs are issued. No warnings are given if conflicting ACFT is not using transponder.
What are the controllers responsibilities when an RA is issued?
- Controller ceases to be responsible for providing separation between that ACFT and any other ACFT affected as a direct consequence of the RA.
- When the pilot reports it, the controller acknowledges the RA and shall not modify the ACFTs flight path or reiterate previously issued instructions until the pilot reports clear of conflict.
Why is traffic information not routinely passed to an aircraft conducting or affected by an RA manoeuvre?
It may be misheard or distract flight crews during a period of very high workload.
NB: There are some circumstances where it is necessary to pass traffic information in the interests of flight safety.
Rather than striving to ensure separation (Which is ATCs role), what is the main aim of ACAS?
To avoid collision as a last resort.
Can TAs and RAs occur when standard separation exists?
Yes, therefore a controller should not immediately assume that separation has been lost or that they are at fault.
What is one cause of an unnecessary RA?
High vertical speed, particularly at low level in congested airspace.
NB: Pilots have been asked to avoid these manoeuvres unless they are justified e.g. after request to expedite climb or for emergency descent.
