SAFE WINGS

This issue…

Dadri Mid-Air Collision

Call Sign Confusion

* For Internal Circulation Only

Flight Safety Magazine of Air India, Air India Express and Alliance Air Issue 44, JANUARY 2015

F l i g h t S a f e t y M a g a z i n e o f A i r I n d i a , A i r I n d i a E x p r e s s a n d A l l i a n c e A i r

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EDITORIAL

Dear Readers, On behalf of Flight Safety Team we wish you a Merry

Christmas and a Happy New Year.

Due to increase in air traffic it is very common to encounter similar

sounding aircraft call signs on the same R/T channel. Many other

occasions manifest themselves where radio confusions has led to

incidents and accidents. This edition has focused on such issues.

ACKNOWLEDGEMENTS

The posting of stories, reports and documents in this magazine does not in any way,

imply or necessarily express or suggest that all the information is correct. It is based

on details gathered from various sources and is for information purpose only. The

Flight Safety Department is making this material available in its efforts to advance the

understanding of safety. It is in no way responsible for any errors, omissions or

deletions in the reports.

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F l i g h t S a f e t y M a g a z i n e o f A i r I n d i a , A i r I n d i a E x p r e s s a n d A l l i a n c e A i r

The Charkhi Dadri mid-air collision occurred on 12 November 1996 over the

village of Charkhi Dadri, to the west of New Delhi, India. The aircraft involved were

a Saudi Arabian Airlines Boeing 747-100B en route from Delhi to Dhahran, Saudi

Arabia, and a Kazakhstan Airlines Ilyushin Il-76 en route

from Chimkent, Kazakhstan, to Delhi. The crash killed all 349 people on board both

planes, making it the world's deadliest mid-air collision, the deadliest aviation

accident to occur in India, and the third-deadliest aircraft accident in the history of

aviation, behind only the Tenerife airport disaster and Japan Airlines Flight 123

The Collision

The Saudi Arabian Airlines (Saudia) Boeing 747-168B, registration HZ-AIH, was

due to operate the first leg of a scheduled international Delhi–Dhahran–

Jeddah passenger service as Flight 763 (SVA763) with 312 occupants on

board; the Kazakhstan Airlines Ilyushin Il-76TD, registration UN-76435, was on a

charter service from Chimkent to Delhi as KZA1907. SVA763 departed Delhi at

18:32 local time. KZA1907 was, at the same time, descending to land at

Delhi. Both flights were controlled by approach controller VK Dutta. The crew of

SVA763 consisted of Captain Khalid Al Shubaily, First Officer Nazir Khan, and Flight

Engineer Edris. On KZA1907, Gennadi Cherepanov served as the pilot and Egor

Repp served as the radio operator.

KZA1907 was cleared to descend to 15,000 feet (4,600 m) when it was 74 nautical

miles (137 km) from the beacon of the destination airport while SVA763, travelling

on the same airway as KZA1907 but in the opposite direction, was cleared to climb

to 14,000 feet (4,300 m). About eight minutes later, around 18:40, KZA1907

reported having reached its assigned altitude of 15,000 feet (4,600 m) but it was

actually lower, at 14,500 feet (4,400 m), and still descending. At this time, Dutta

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advised the flight, "Identified traffic 12 o'clock, reciprocal Saudia Boeing 747, 10

nautical miles (19 km). Report in sight."

When the controller called KZA1907 again, he received no reply. He warned of the

other flight's distance, but it was too late. The two aircraft had collided, the tail of

KZA1907 cut through SVA763's left wing and horizontal stabiliser. The crippled

Boeing quickly lost control and went into a rapidly descending spiral motion toward

the ground with fire trailing from the wing. The Boeing broke up in the air under

the stresses before the wreckage hit the ground at almost 1,135 km/h (705 mph).

The Ilyushin remained structurally intact as it went in a steady but rapid and

uncontrolled descent until it crashed in a field. Rescuers discovered four critically

injured passengers from the Ilyushin, but they all died soon afterwards. Two

passengers from the Saudia flight survived the crash, still strapped to their seats,

only to die of internal injuries soon after. In the end, all 312 people on board

SVA763 and all 37 people on KZA1907 were killed.

Captain Timothy J. Place, a pilot for the United States Air Force, was the sole

eyewitness to the event. He was making an initial approach in a Lockheed C-141B

Starlifter when he saw that "a large cloud lit up with an orange glow".

The collision took place about 100 kilometres (60 mi) west of Delhi. The wreckage

of the Saudi aircraft crashed near Dhani village, Bhiwani District, Haryana. The

wreckage of the Kazakh aircraft hit the ground near Birohar village, Rohtak

District, Haryana. This was the first mid-air collision between two commercial

aircraft since the Dniprodzerzhynsk mid-air collision in 1979; it was succeeded by

the mid-air collision between a Bashkirian Airlines Tupolev Tu-154M and a DHL

Boeing 757 over Germany in July 2002 and then by the mid-air collision between

a Gol Boeing 737 and an ExcelAire Embraer Legacy over Amazonia in

September 2006.

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PASSENGERS AND CREWS

Saudi Arabian Airlines Flight 763 The captain of the flight, aged 45, was a veteran pilot with more than 9,800 flying

hours to his credit. A total of 289 passengers were on board which consisted of

215 Indians , 40 Nepalese, 3 Americans and 31 people of other nationalities. There

were 23 crew members, including five anti-terrorism officials.

Kazakhstan Airlines Flight 1907 The 44-year-old captain of Flight 1907 was also highly experienced, with more

than 9,200 flight hours under his belt. A company from Kyrgyzstan chartered the

flight, and the passenger manifest mostly included ethnic Russian Kyrgyz citizens

planning to go shopping in India. There were 27 passengers and 10 crew on board.

Investigation And Final Report

The crash was investigated by the Lahoti Commission, headed by then-Delhi High

Court judge Ramesh Chandra Lahoti. Depositions were taken from the Air Traffic

Controllers Guild and the two airlines. The flight data recorders were decoded by

Kazakhstan Airlines and Saudia under the supervision of air crash investigators in

Moscow and Farnborough, England, respectively. The ultimate cause was held to

be the failure of Kazakhstan Airlines Flight 1907's pilot to follow ATC instructions,

either due to cloud turbulence or due to communication problems.

The commission determined that the accident had been the fault of the Kazakh Il-

76 commander, who (according to FDR evidence) had descended from the

assigned altitude of 15,000 to 14,500 feet (4,600 to 4,400 m) and subsequently

14,000 feet (4,300 m) and even lower. The report ascribed the cause of this

serious breach in operating procedure to the lack of English language skills on the

part of the Kazakh aircraft pilots; they were relying entirely on their radio operator

for communications with the ATC. The radio operator did not have his own flight

instrumentation but had to look over the pilots' shoulders for a reading. Kazakh

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officials stated that the aircraft had descended while their pilots were

fighting turbulence inside a bank of cumulus clouds.

Indian air controllers also complained that the Kazakh pilots sometimes confused

their calculations because they are accustomed to using metric altitudes and

kilometre distances, while most other countries use feet and nautical miles.

Just a few seconds from impact, the Kazakh plane climbed slightly and the two

planes collided. This was because the radio operator of Kazakhstan 1907

discovered only then that they were not at 15,000 feet and asked the pilot to

climb. The captain gave orders for full throttle, and the plane climbed, only to hit

the oncoming Saudi plane. The tail of the Kazakh plane clipped the left wing of the

Saudi jet, severing both parts from their respective planes. Had the Kazakh pilots

not climbed slightly, it is likely that they would have passed under the Saudi plane.

The recorder of the Saudi plane revealed the pilots recited the prayer that is

required, according to Islamic law, when one faces death. The counsel for the ATC

Guild denied the presence of turbulence, quoting meteorological reports, but did

state that the collision occurred inside a cloud. This was substantiated by the

affidavit of Capt. Place, who was the commander of the aforementioned Lockheed

C-141B Starlifter, which was flying into New Delhi at the time of the crash. The

members of his crew filed similar affidavits.

Furthermore, Indira Gandhi International Airport did not have secondary

surveillance radar, which provides extra information, such as the aircraft's identity

and altitude, by reading transponder signals; instead the airport had primary

radar, which produces readings of distance and bearing, but not altitude. In

addition, the civilian airspace around New Delhi had the same corridor for

departures and arrivals. Most areas separate departures and arrivals into separate

corridors. The airspace had one civilian corridor because much of the airspace was

taken by the Indian Air Force. Due to the crash, the air-crash investigation report

recommended changes to air-traffic procedures and infrastructure in New Delhi's

air-space:

Separation of inbound and outbound aircraft through the creation of 'air corridors'

Installation of a secondary air-traffic control radar for aircraft altitude data Mandatory collision avoidance equipment on commercial aircraft operating in

Indian airspace Reduction of the airspace over New Delhi that was formerly under exclusive

control of the Indian Air Force The Civil Aviation Authorities in India made it mandatory for all aircraft

flying in and out of India to be equipped with an airborne collision avoidance

system.

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The use of similar call signs by aircraft operating in the same area on the same

RTF frequency often gives rise to potential and actual flight safety incidents. This hazard is usually referred to as “callsign confusion”.

The potential safety consequences of an aircraft taking and acting on a clearance intended for another can cause a serious incident. The following, not being a

comprehensive list, are some examples of the potential outcomes of such a situation:

The aircraft takes up a heading or routing intended for another; The aircraft commences a climb or descent to a level to which it has not been

cleared; The aircraft set an speed intended for another The aircraft leaves the appropriate frequency;

In responding to a message, the aircraft blocks a transmission from the intended recipient;

The intended recipient does not receive the clearance, and fails to take up the desired heading or routing, or fails to climb or descend to the cleared level;

The controller misunderstands the intentions of aircraft under his/her control;

The controller issues a clearance to the wrong aircraft, and/or fails to issue a clearance to the intended aircraft;

The workload of controllers and pilots is increased because of the necessity to resolve the confusion.

Aircraft call signs

Three different types of aircraft call sign may be encountered, as follows:

Type (a) The characters corresponding to the registration marking of the aircraft (e.g. ABCDE). The name of the aircraft manufacturer or model may be used as a

prefix (e.g. AIRBUS ABCDE);

Type (b) The telephony designator of the aircraft operating agency, followed by

the last four characters of the registration marking of the aircraft (e.g. EXPRESS-INDIA BCDE);

Type (c) The telephony designator of the aircraft operating agency, followed by the flight identification (e.g. EXPRESS-INDIA 1234).

The full callsign must be used when establishing communications.

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After satisfactory communication has been established, abbreviated call signs may be used provided that no confusion is likely to arise; however, an aircraft must use

its full call sign until the abbreviated call sign has been used by the ground station.

Call signs may be abbreviated only in the manner shown below. Examples of full and abbreviated call signs are shown on Table 1 below.

Table 1 – Examples of full call signs and abbreviated call signs

Type (a) Type (b) Type (c)

Full call sign AIRBUS ABCDE EXPRESS-INDIA ABCDE

EXPRESS-INDIA 1234

Abbreviated call

sign AIRBUS DE or AIRBUS CDE

EXPRESS-INDIA DE or EXPRESS-INDIA CDE

No abbreviated

form.

Most airline call signs belong to type (c) for which there is no abbreviation. Therefore,

abbreviations such as “EXPRESS-INDIA 34” are not permissible. An aircraft is not

permitted to change its call sign during flight, except temporarily on the instruction of an air traffic control unit in the interests

of safety.

In order to avoid any possible confusion, when issuing ATC clearances and reading back such clearances, controllers and pilots

must always add the call sign of the aircraft to which the clearance applies.

Numeric vs. Alphanumeric call signs

Many airlines continue to use their IATA commercial flight numbers as call sign

suffixes. However, because they tend to be allocated in batches of sequential and very similar numbers, call sign confusion occurs.

Several airlines have switched to alphanumeric call signs reasonably successfully in recent years. However, if every operator adopts alphanumeric call signs, the limited choices available within the maximum of 4 elements allowed within a call

sign suffix means that call sign confusion, similar to the existing numeric system, is likely to occur.

Before changing to an effective all-alphanumeric call sign system, which involves a significant amount of work, it is recommended that operators review their existing

numeric call sign system to deconflict any similar numeric call signs. Where there is no solution to those call signs that have a potential for numeric confusion,

alphanumeric call signs can be adopted.

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Selection of call signs

The best defence against call sign confusion consists in eliminating, or reducing to an

absolute minimum, the chance of having two (or more) aircraft with phonetically similar call signs on the same RTF frequency at the same

time.

To be effective, such a strategy requires action on a regional and international basis. Call sign suffixes must be allocated according to a

deliberate, coordinated policy that prevents a confliction arising in the first place.

Until such a strategy is in place, aircraft operators should attempt to assign call signs in

such a way that confliction with their own and other scheduled traffic does not arise.

Where commercial flight numbers are not used, operators should ensure that airport

information systems can cope with the conversion of RTF call signs (for ATC use) to commercial flight numbers (for passenger and airport use).

Practical experience, suggests that certain formats are especially likely to lead to confusion. Examples are: number sequences beginning with a low number; long

number sequences (four or more); repeated digits.

Common Causes For Call Sign Confusion

The following are some examples of the more common causes for call sign

confusion:

Airlines allocate commercial flight numbers as call-signs; these are normally consecutive and therefore similar (e.g. EXPRESS-INDIA 1431, EXPRESS-INDIA 1432, etc.)

Airlines schedule flights with similar call signs to be in the same airspace at

the same time.

Call signs coincidentally contain the same alphanumeric characters in a

different order (e.g. AB1234 and BA 2314).

Call signs contain repeated digits (e.g. EXPRESS-INDIA 555).

Recommendations for aircraft operators

Coordinate with other operators to reduce to a minimum any similar

numeric and alphanumeric elements of call signs. Start flight number element sequences with a higher number (e.g. 6).

Do not repeatedly use call signs involving four digits and, wherever possible, use no more than three digits.

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Do not use the same digit repeated (e.g. EXPRESS-INDIA 555). If alphanumeric suffixes are to be used, coordinate letter combinations with

other airspace and airport users. If similarly numbered call signs are inevitable, allow a significant time

and/or geographical split between aircraft using similar call signs or convert one to alphanumeric and the other to only numeric.

Do not use similar/reversed digits/letters in alphanumeric call signs (e.g.

EXPRESS-INDIA 87MB and EXPRESS-INDIA 78BM). Implement a call sign deconfliction programme, to review and if necessary

amend call signs.

Recommendations for flight crew

Always use headsets during times of high RTF loading. Always wear a

headset when members of the flight crew are involved in other tasks and may not be monitoring the RTF.

Do not clip transmissions.

Use full RTF call signs at all times, unless call sign abbreviation has been introduced by ATC.

Use correct RTF procedures and discipline at all times. If in doubt about an ATC instruction, do not use read back for confirmation.

Instead, positively confirm instructions with ATC. This procedure should also

be followed if any doubt about a clearance exists between flight crew members.

Question unexpected instructions for any stage of flight. Take extra care when members of the flight crew are involved in other tasks

and may not be monitoring the RTF.

At critical stages of flight actively monitor ATC instructions and compliance with them.

Advise ATC if any of the following situations is observed:

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a) two or more aircraft with similar call signs are on the RTF frequency; b) it is suspected that an aircraft has taken a clearance not intended for

it;

c) it is suspected that another aircraft has misinterpreted an instruction; d) a blocked transmission is observed.

Although not an official procedure, many pilots hearing that two transmissions block each other call out “Blocked”, after which all transmitting parties try once more to pass their messages.

After a flight where an actual or potential call sign confusion incident is observed, file a report using mandatory incident reporting system or

voluntary incident reporting system as appropriate.

Recommendations for air navigation service providers Ensure that aircraft operators are made aware of any actual or potential call

sign confusion reported by air traffic controllers.

Recommendations for air traffic controllers

Use correct RTF phraseology,

procedures and discipline at all

times. Do not clip

transmissions.

Ensure clearances are read back

correctly. Do not use read-back time to execute other tasks.

Monitor flight crew compliance with RTF

call sign use. Take extra care

when language

difficulties may exist. Advise adjacent sectors/airports if it is felt that potential confusion may exist

between aircraft likely to enter their airspace. Warn the pilots of aircraft on the same RTF frequency having similar call

signs that call sign confusion may occur. If necessary, instruct one or both

aircraft to use alternative call signs while they are on the frequency. A transmission could be blocked when two or more aircraft are responding

to the same clearance. Typically the controller would hear a partial or garbled readback. If a blocked transmission is suspected, ensure that both

aircraft retransmit their messages and confirm carefully that a clearance has not been taken by an aircraft for which it was not intended.

Where an actual or potential call sign confusion incident is observed, file a

report using the mandatory incident reporting system or voluntary incident reporting system as appropriate.

PROMISING A SAFER SKY, AIR INDIA, AIR INDIA EXPRESS & ALLIANCE AIR

We give utmost importance to your valuable comments and feedback. Please do mail us at

airsafety@airindia.in or

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Editorial: -Bhavish B S, Capt V. Kulkarni Designed by Bhavish BS

SANTA-EXPRESS25DEC

requesting permission to land...