Edition 44 JANUARY 2016 - CLICK

SAFE WINGS
Flight Safety Magazine of Air India, Air India Express and Alliance Air
Issue 44, JANUARY 2015
This issue…

Dadri Mid-Air
Collision

Call Sign Confusion
* For Internal Circulation Only
SAFE WINGS
January Edition 44
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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Flight Safety Magazine of Air India, Air India Express and
Alliance Air
January Edition 44
The Charkhi
SAFE WINGS
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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SAFE WINGS
January Edition 44
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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Flight Safety Magazine of Air India, Air India Express and
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January Edition 44
SAFE WINGS
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 Il76 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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SAFE WINGS
January Edition 44
officials stated that the aircraft had descended
fighting turbulence inside a bank of cumulus clouds.
while
their
pilots
were
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.
5|Page
Flight Safety Magazine of Air India, Air India Express and
Alliance Air
January Edition 44
SAFE WINGS
T
he 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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SAFE WINGS
January Edition 44
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
Full call sign
Abbreviated
sign
call
Type (a)
Type (b)
Type (c)
AIRBUS ABCDE
EXPRESS-INDIA
ABCDE
EXPRESS-INDIA
1234
AIRBUS DE or AIRBUS CDE
EXPRESS-INDIA DE
No
abbreviated
or EXPRESS-INDIA
form.
CDE
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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Flight Safety Magazine of Air India, Air India Express and
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January Edition 44
SAFE WINGS
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, EXPRESSINDIA 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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SAFE WINGS
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January Edition 44
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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Flight Safety Magazine of Air India, Air India Express and
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January Edition 44
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SAFE WINGS
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.
Flight Safety Magazine of Air India, Air India Express and
Alliance Air
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SANTA-EXPRESS25DEC
requesting permission to land...
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PROMISING A SAFER SKY, AIR INDIA, AIR INDIA EXPRESS & ALLIANCE AIR
Editorial: -Bhavish B S, Capt V. Kulkarni
Designed by Bhavish BS