There are standard International Rules applicable for all aircrafts that operate in Airways or outside them. Generally, the vertical separation between aircrafts is 1000 feet. Thus, aircraft flying East maintain an odd level whereas those flying West will fly an even level below a certain height.
However as the airspaces become more congested, and to
accommodate more flights, certain airspaces have reduced the vertical separation at higher levels. Only aircrew who are certified are allowed to operate in these higher reduced separation levels. Further, only approved aircrafts, of which the Boeing 777 is one of them, are allowed into such airspaces.
In areas where ground radar are available, aircraft horizontal separation are controlled by the ground air traffic controllers. Where no radar services are available, time restrictions are imposed, usually 10 minutes separation or about 70 to 85 miles apart, depending on the speed of the aircraft.
Traffic alert and Collision Avoiding System
In very congested airspaces where safe separation are insufficient, most modern aircraft, the Boeing 777 included, are installed with an equipment known as TCAS or Traffic alert and Collision Avoiding System that alert the pilots of any traffic that is on a collision course.
Basically, the TCAS is an airborne equipment that send a signal to another aircraft that is also equipped with a similar equipment. From the replies, the system
analyze the intruding aircraft's altitude, closure rate, projected flight path to predict the penetration of the airspace above the threaten aircraft.
The system then display the intruding aircraft visually in the cockpit instrument panel and aurally alert the pilot, (such as, "Climb, Climb, Climb!' or 'Descent, Descent, Descent !) of the potential threat.
When the threat situation has passed, the aural alert 'Clear of Conflict !' will tell the pilot that the
dangers have been averted.
Information of Interest to Passengers
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The advice of having the seat belts on at all times even when they have been switched off is relevant because avoiding maneuvers to prevent collision are
unforeseen and can happen at any time.
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When any of such avoiding alerts that require a vertical change of altitude, the pilot is expected to act and comply within two and a half seconds. Therefore, such maneuvers require a pretty rapid response but are not critical. If the maneuver is correctly handled, there is very little discomfort to passengers.
