No two airlines can have same call-signs if they are scheduled within two hours of each other or similar identifiers, as per the fresh norms issued by DGCA today to avoid "confusion", which have led to near-miss incidents in the past.

The latest regulations by the Directorate General of Civil Aviation (DGCA) have been issued to airport operators and airlines mandating that carriers should not have visually or aurally similar identifiers.

A call-sign is the airline code and the flight number. During communications between the Air Traffic Control (ATC) and the pilot onboard a flight, phonetic versions for alphabets are used worldwide.

"Use of similar call-signs by aircraft operating in the same area, at the same time, and on same ATC frequency often give rise to potential and actual confusion leading to misunderstanding by pilots and controllers," the notification said.

"As a result, one aircraft may act on the clearance meant for another aircraft, which would result in runway incursions, level bust, loss of separation, airprox," it added.
As per the new norms, no two airlines can have same call-signs if they are scheduled within two hours of each other from the same airport.

It also says that no two flights of the same carrier can have identical call-signs if they are scheduled within 12 hours of each other.

As per these rules same digits can not be used to form a call sign.
The regulator has also stipulated that four-digit call signs can only be used when a three digit sign is not available.

The DGCA had set up a committee last year comprising of its officials, domestic airlines as well as the Delhi Airport, to look into similar call-signs used by carriers and suggest measures to remove the ambiguity.