Call sign confusion still there - Curt Lewis

Similar call signs ring alarm bells for flight safety, DGCA forms panel (India)

DGCA has formed a committee to review instances of aircraft coming dangerously close to each other (called airprox) due to "confusing/similar call signs". 

NEW DELHI: Similar call signs of commercial flights have set alarm bells ringing in the Indian aviation safety regulatory agency. The Directorate General of Civil Aviation (DGCA) has found instances where air traffic control (ATC) gave instructions to one flight and the pilots of some other similar call sign assuming it to be for him. Similar call signs can lead to confusion trouble, for example, when AB 103 and CD 103 or GH 343 and GH 433 are flying around the same time at the same place and instructions for one can be misunderstood to be for the other by their pilots.

Given its serious safety implication, DGCA chief M Sathiyavathy has formed a committee to review instances of aircraft coming dangerously close to each other (called airprox) due to "confusing/similar call signs" under the chairmanship of joint DGCA Lalit Gupta.

While this panel has to submit its report by March 18, the regulator has already decided that flight numbers will not end in 0 or 5. "The altitude that a plane is to fly at is conveyed by ATC in figures ending in zero, for example 320 which means it should be at an altitude of 32,000 fleet. A flight with that call sign, say XY 320, may mistake that the ATC has asked it to change altitude," said a senior DGCA official.
Similarly, the heading or direction in which a plane should go is given in figures ending in five. Hence, flight numbers will not end with five also.

"We analyzed the airprox data of some years and found similar call signs being responsible in many cases. Some regions have been found to be vulnerable to this problem where the ATCs that a plane is flying through belong to different agencies like Airports Authority of India, defence and foreign countries," said the official.

These vulnerable regions are: Northeast when planes change ATC from AAI, Indian Air Force and Bangladesh; south India where ATC shifts from AAI to Sri Lanka and there are numerous overflying aircraft and finally Jammu and Kashmir where ATC shifts between AAI and IAF.

These areas have witnesses problems like an airline's flight 273 beginning to descend when that airline's flight 237 was asked to do so.

The Lalit Gupta panel is studying how Eurozone and Gulf deals with this issue as those regions also face the same problem. The DGCA has taken some interim decisions like not allowing similar sounding call signs or signs with same digits in their numeric part -- every call sign has the airline code followed by the flight number like AI 101 which denotes flights 101 of Air India -- to be flying within a space of upto two hours in the same region. Similarly, flights numbers like XY 222 or BC 333 will not be allowed.

The ATC had alerted DGCA about the confusion caused by this reason in November 2014. The ATC top brass had formally asked the regulator to end this confusion by ensuring that no two flights meant to operate at an airport around the same time get similar call signs.

According to a minutes of a meeting held on this issue in November 2014, ATC officials had said: "airlines using four-digit call signs for smaller aircraft and three-digit call signs for Airbus A-320/Boeing 737 (is) causing confusion between pilots and air traffic controllers as the last three digits of a flight number are similar and operating within the same hour. (ATC) requested DGCA/airport operators to look into this issue and allocate flight numbers which are not similar to avoid confusion.... conflicting call sign issue needs to be resolved by airline before the approval of schedules otherwise their slots will be kept in abeyance."

The ATC brass had then submitted a list of confusing call sign flights operating almost at the same time at the same place across busy Indian airports.

Call of confusion:
XY*2460: Reaches Mumbai at 1.40pm from Hyderabad
XY*460: Reaches Mumbai at 1.45pm from Chennai
XY*647: Mumbai-Jamnagar at 11am
YZ*447: Mumbai-Srinagar at 11am
XY*244: Arrives in Mumbai at 10.45am from Ahmedabad
YZ*234: Arrives in Mumbai at 10.45am from Bengaluru
XY*306: Delhi-Mumbai at 10.25am
XY*603: Delhi-Srinagar at 10.50am
XY*107: Delhi-Bengaluru at 7.30pm
YZ*107: Delhi-Mumbai at 8.30pm
YZ*181: Delhi to Mumbai at 9.30am