There have been several instances of two aircraft flying close to each other, triggering panic among passengers and sometimes resulting in air crashes. So, what should the safe distance be between two aircraft flying in the same air space?
According to baatraining.com, the distance between two flying commercial aircraft may vary at different flight phases and altitudes during a take-off and landing or at cruise altitude. This vertical and horizontal aircraft separation is under the control of specific aviation regulations and may vary in different regions.
As per US-based Federal Aviation Administration guidelines, commercial aircraft flying below 29,000 feet must maintain a vertical separation of 1,000 feet.
Any higher and the separation increases to 2,000 feet, except in airspace, where Reduced Vertical Separation Minimum (RVSM) applies. RVSM approval allows aircraft to fly with a vertical separation of 1,000 feet reduced from 2,000 feet between FL290 (flight level 29,000 sq ft) and FL410 (flight level 41,000 sq ft) inclusive.
Over the ocean, beyond radar coverage, the vertical separation minimum can be as little as 1,000 feet.
Since aircraft cause wake turbulence (disturbance in the atmosphere that forms behind an aircraft as it passes through the air) that may affect other aircraft flying the same track at the same altitude, horizontal separation is much greater than vertical. In controlled airspace, the required minimum horizontal separation between aircraft flying at the same altitude is five nautical miles, which is just over nine kilometres. When an aeroplane is departing, Air Traffic Controllers (ATCs) can place aircraft much closer to each other than at cruise altitude.
Thus, in the terminal area airspace, horizontal separation decreases to three nautical miles.
ATCs in some countries also allow simultaneous take-offs on parallel runways. But once they take off, the aircraft turn in opposite directions, leading to a safe separation between the two.
Source: BAAtraining.com and aviationvoice.com