a. No foul play could have been
involved. It's just that there are some poor English speakers and dyslexic
pilots out there. With the .005khz spacings you can now have six digit
frequencies to remember and dial in. (eg 126.85Mhz may now have become
126.825Mhz). Easy to transpose the latter three digits. However that's why
it is always SOP to initiate a call to your new agency after a check-in. The
possibility is that the Russian pilot may have mis-dialled into an active
frequency and was either creating confusion on there, awaiting a chance
to check in, or just taking some time to sort himself out. The only safe way
is to grease-pencil the new freqs on the perspex as you hear it. There's a very simple explanation why he failed to respond to
repeated calls from ATC. He just wasn't on that frequency. Usually these
type mistakes, which are very common, are encountered in an approach or departure
climb type scenario - where they used to be much more hazardous. But now in
upper airspace Man's ingenuity has created greater hazards (see
b. And of course they were up there at 36,000ft (Flt Lvl 360) in
RVSM country (Reduced Vertical Separation Minima where aircraft previously
had to utilise 2000ft vertical separation for opposite direction or crossing
traffic - because of the accuracy limitations of the lowest common
denominator barometric altimeters and autopilots).
c. A method that used to be used to avoid this sort of fiasco was
for the military to utilise 243.00mhz (International Distress UHF) and
civilian aircraft to listen out on a silent common frequency of 121.5.00
(half of 243Mhz) - which is the civil VHF distress frequency. However
because of the traveling goat acts that abuse silent frequencies, there is
never any guarantee that someone who ATC calls in an emergent situation actually
IS going to be listening out on that silent frequency.
d. So why did this automatically have to be a disaster? Pilots have been
saying for ten years that the ability of modern navigational kit to
the centre-line of airways was always going to cause this sort of NOCOMM
collision - because the high closure speeds defeat visual acquisition, TCAS
and the ability to think, realize, advise and react. With modern
GPS-equipped aircraft, every time we go flying we go either directly over or
under other traffic; and the big sky principle no longer applies. Airways are 10 nm wide,
don't regulators require all operators to offset 1 mile right (or even 100m)
in the cruise phase to reduce the chances of this unfortunate accident
re-occurring. Even in RVSM airspace, there is sufficient space to allow this
principle to be applied until the aircraft begins descent. ICAO has been
"looking into it" for over ten years. The problem is described
e. Once placed in jeopardy by the situation
described in d. (above), a single-party TCAS solution is still open to the
variability and unpredictability of the other aircraft's last second
flight-path changes (based on misinterpretation of a last-second visual
acquisition or ATC urgent instruction). That seems to have been the
nightmare scenario for this accident.
From a Pprune Posting
From what I can gather, the DHL pilot was responding correctly to TCAS RA to fly down.
Now if the TU154 was in RVSM,
shouldn't it have had TCAS installed as a requirement?; so shouldn't the
two TCAS computers have co-ordinated the avoidance action?
In any case, it is an accident which should have us all reflect that even in
one of the best controlled airspaces with all the modern airborne equipment
etc. we still need to be scanning that sky or at least scanning the ND
continously for suspect TCAS targets in order to have as early a warning as
possible of potential threats.
Another thing which I hope will *not* happen after this accident is that
pilots will become wary of following TCAS RAs if it transpires that the DHL
pilot still got himself into trouble by following the TCAS instruction. We
could end up in the same trap where pilots "analyse" GPWS warnings during an
I did have a TCAS RA once during cruise (FL350, European airspace) and since
it was an opposite (uncontrolled!) fast military traffic, our TCAS didn't
have time to give a "TRAFFIC, TRAFFIC" warning and we were issued with the
"DESCEND, DESCEND" warning immediately, accompanied by the controller
"screaming" a lateral avoidance vector at the same time.
of some pilots to appropriately respond to avoiding action has already been
discussed at length
ATC, the following things make me wonder....
If the aircraft were at the same level inbound from the Italian and
German sectors respectively, then surely the Swiss sector should have
co-ordinated a different level for one of them prior to entering the
sector (less than 10 minutes before impact)?
Does the Swiss Sector have MTCD (Medium Term Conflict Detection) which
would give about 10 -15 minute warning of conflict? If so, what was
done with this MTCD information?
Surely it is not normal to leave a separation instruction so late that
a non-compliance immediately causes a bad situation to turn into a
At what point should ATC leave the avoidance to the respective TCAS's,
Will pilot's respond to ATC or TCAS as priority ?
These are questions that are raised in my mind as an ATC. No intent to
1. The entry levels
via those two points were correct for the direction of flight of the
two aircraft. The 757 , via SRN, would have been on the freq. for
quite a wee while before the T154 in at KPT.
2. Yes, Zurich does have Short Term Conflict
Alert , but it seems it was off for maintenance. Usual
procedure to do so during the night shift.
3. I also feel very uncomfortable about the ATCO waiting approx. 1
min. prior to "loss of separation" before instructing an aircraft to
change level. Compounded by the fact the pilot did not immediately
respond/comply. It's a sad reality that pilots do not always do what
we tell them to do immediately.
But what is emerging and is of real concern regarding TCAS is that the
DHL TCAS " Descend" command came AFTER the Tu154 started to comply
with the ATCO's instruction to descend to FL350. Why would it give a
descent command against conflicting traffic already descending ?
TCAS alerting is based on
prediction of a 'Closest Point Of Approach' (or CPA).
If the predicted CPA is too small (horizontal and vertical values depend on
Altitude - the higher you are the bigger the predicted 'miss' must be for
TCAS to consider it safe) then a Resolution Advisory (RA) will be generated
once the aircraft are within the RA Alerting Time.
This value also varies with altitude, from (if I recall correctly - manual
not to hand) some 15 seconds at low levels to 35 seconds at high level.
The RA is preceded by a Traffic Advisory, 10 - 15 seconds earlier, depending
Since it is a time parameter, a 'nose to nose conflict in fast jetliners' is
not an issue. (i.e. the greater the rate of closure, the greater the
distance at which the alerts are generated.)
However, the increased time allocated to Alerts at high level does not
translate into more time for 'assessment and reaction'. The reason more time
is given is because:
a) Altimeter inaccuracies mean that a bigger vertical miss must be
provided by TCAS to be sure of safety. I.E. aircraft could be at the same
level even though in reported altitude terms they could look like they are
a couple of hundred feet apart. Hence the safe separation required is
Worst Case scenario of altimeter inaccuracy, X 2, + required actual
b) High altitude make the aircraft less maneuverable (IAS / TAS
The alerting times are selected so that the aircraft has enough time to go
from predicted co-altitude with intruder to safe separation, plus 5 seconds
of reaction time for the crew.
As another point, there are various eventualities that can delay or even
prevent the TCAS response. However to go into them here would be verging on
Typically, there are two kinds of TCAS advisories,
TA - Traffic Advisory
and RA - Resolution Advisory.
Traffic advisory TA, is activated when another aircraft is about to intrude
the TA protective envelope within approximately 40 sec. The envelope is 0.75
nm radius and 850 ft above and below your a/c. The TA will provide both
visual and aural cues, ie the display will turn the color of the traffic
from white to amber with the aural warning, i.e "Traffic, Traffic"
The Resolution advisory RA, is activated when another a/c is about to
intrude the RA protective area within approximately 20 sec. The RA
protective envelope is 0.30 nm and 600 ft above and below your a/c. The
color of the symbol will now turn red and the aural warning and the
maneuvering command will be displayed on the VSI with the aural warning, i.e
"Climb, Climb Now!" "Climb, Climb Now!" Compliance with the commanded
maneuver is required with 5 sec (2.5 for enhanced RA) of the aural warning
with at least +/- 0.25 G maneuver.
"Clear of Conflict" will be announced once the traffic is well cleared.
There is a new version of TCAS called TCAS VII that is not widely used or
required but it provides both vertical and lateral RA.
1. TCAS will not be
able to detect a/c that do not have operating transponder.
2. They will not provide
RA against non-altitude reporting transponder.
3. It has an
automatic function to make coordination with the other TCAS-equipped a/c in
case of RA so that both a/c will not move in the same direction.
What is described above is how a TCAS II would operate and it is believed
that the B-757 was probably equipped with such a system. No idea what was on
the Tupolev, if any...
Quest: Why does TCAS make you go down instead of turning
left/right to avoid other aircraft?
Because TCAS uses Mode 'c' to arrange deconfliction. At the moment it does
not have sufficiently good lateral resolution to ensure avoidance.
Swiss ATC media conference just held
Today’s mid-air collision over Southern Germany
is, according to Skyguide (the Swiss ATC), the
result of simultaneously initiated descents by both
the aircraft that eventually collided. In the case
of the Russian Tupolev TU-154, the descent was
initiated based on ATC instructions, whereas the
descent of the B-757 freighter was triggered by its
Anton Maag, Chief of Zurich-Kloten Control Tower,
and Skyguide Spokesman Patrick Herr, held a press
conference today, Tuesday, to review the events of
the previous night.
Between 2300 and 2400, there were no unusual
occurrences in Swiss air control space, with only a
few aircraft in the air. Swiss ATC was handed over
the Russian TU-154, which was on a East-to-West
routing by German ATC at around 2330, whilst the
B-757 freighter, on a South-to-North routing, was
handed over by Italian ATC to Swiss ATC at 2323.
Both planes were at an altitude of 36000 feet
(around 11500 meters).
The Swiss controller thus advised the Russian
aircraft to descend to a lower flight level.
According to Skyguide’s Anton Maag, it required
three attempts before this advice was confirmed by
the Russian crew. As a result, the Russian aircraft
began its descent very late. At the same time, the
crew of the B-757 freighter was advised for reasons
unclear by its TCAS to descend as well. Obviously,
according to Maag, this command has to be followed
The eventual collision happened at an altitude of
35000 feet between 2335 and 2336. Both aircraft
remained visible for a number of sweeps on the radar
screen. Maag says there were no linguistic problems
between the Swiss controller and the Russian crew,
whilst Herr mentioned two “sticking points” in the
context of this crash. “First, why did the Russian
pilot not react immediately? Second, why did the
TCAS on board the B-757 advise its crew to dive?” So
apart from the question as to
why the TCAS on board
the B-757 did not recognize the other aircraft's
descent, both aircraft were tuned to the same radio
frequency, so they could both simultaneously hear
their respective interaction with Zurich-Kloten
the Tu-154 was not TCAS-equipped, the 757 TCAS
instruction would have been to a predetermined
schedule and not an absolute determination computed
from both aircraft's TCAS interaction....and would
therefore seem to be a basic failing of TCAS. In
other words a single party TCAS RA might lead you
into danger rather than out of it when the other
party is late responding to ATC instructions.
It sounds very much as if the Tu-154 was avoiding visually in response to
ATC and the 757
was following the TCAS instructions for a singe station RA (Resolution Alert). Probably
one (or neither?) aircraft turned right (the old rules).
Since Swiss ATC have
put their side, I feel the following thoughts:
1. 8-10NM (at 90deg) is far too
late to describe as even "less than ideal". As someone else said, it
will be interesting to see what urgency prefixes were applied to the
2. A Plan B is required here - the
second call maybe, and certainly the third call should surely have
been to the DHL ac? There are a number of legitimate reasons why the
Russian aircraft did not, or could not respond. There is, for
instance, a known issue with some radios in our fleets where they "go
to sleep" and aircraft have not responded for minutes to call. Advice
to us - if you don't hear something for a long time (which would be
along time at night), click the Tx key...
3. IMHO, the Russian pilot could
only be "blamed" if he read back the instruction, and only THEN did
4. Leaving it so late to start
avoiding action, not only increases the possibility of collision by no
response (which did not happen here), but TCAS getting involved.
5. Hard to blame TCAS ??
Basically, the 2 anti collision systems (ATC and TCAS) were both
"working" in a "just in time" manner - and unfortunately took the
50:50 worst case. TCAS is designed to be a backstop to ATC, and hence
is "just in time". ATC should
I do not like pointing the finger, but am very concerned by Swiss ATC
throwing the mud. IMHO, in that they have started throwing it, its
alright to throw some back...
ISSUES for Consideration
- Respond to TCAS resolution advisories only to the extent to which the
cues are provided on your EADI or EVSI. An RA will often require no more
than 1500 fpm climb or descent to deconflict the traffic. At high Mach
numbers and flown manually, the pitch change is remarkably small. A panic
large input may cause additional problems or even an upset.
- Resist the temptation, especially at night, to try and
second-guess the TCAS RA. In RVSM, an aircraft 1000 feet below you might
look as if it’s actually above and vice versa. Trust the TCAS and use it
to enhance your mental model of your bit of airspace. You may think you’ve
worked out the best avoidance, but the TCAS has a
contract with the conflicting traffic and has worked out the best
avoidance manoeuvre. Remember, the other target may be simultaneously
involved in avoiding another aircraft.
- If your aircraft is fitted with an early type of display, remember
that the azimuthal error in TCAS can be up to 20º, which means that the
intruder could be either left of the nose or right of the nose. TCAS is
designed to provide only vertical deconfliction, so again don’t try to
second guess it.
- Listen out on your frequency, try and plot other aircraft in your
mental model, and think about where conflicts might arise. If necessary
inform ATC of any concerns you have about another aircraft. They will be
more than happy to put your mind at rest.
- Make sure that at least one of you is monitoring 121.5 at all times.
Someone may have urgent news for you, and you may not be talking to them
at the time
One of our 737s
returning from bjv was in the vicinity at the time.
The capt has told me that he heard an American voice suddenly
calling TCAS DOWN, and looking to their right, saw the fireball
at around 36,000 feet, lighting up the sky all around.
Presumably this was the 757 calling.
Both crew a little shaken to have seen it.
The B757-200SF was reg:
A9C-DHL, c/n 22175 - on flight DHX611. ( a PF
operated by DHL Bahrain BAH/BGY/BRU. (Bahrein/Bergamo/Brussels))
The DHL plane had a TCAS collision avoidance system on board, which U.S.
regulators require for passenger aircraft and have ordered phased in for
Tupolev registration is
The Russian jet was headed to Barcelona, Spain, from Moscow,
originating in Ufa, Russia, and had just made a stop in the German city of
I doubt that the T154 had
RVSM compliance and BOTH aircraft require compliance to use 1000' separation
above FL290. However it appears both were at the same cleared level. One of
the a/c (probably the TU134) had just passed from Munich to Zurich ATC prior
to the collision. Hope the TU-154 did not start descending in response to
ATC, simultaneously as the DHL started a TCAS descent...
It's amazing the
number of ATC frequency changes to transit this area of Europe; you can
cross the States on less.
it goes without saying that our thoughts here go out to those involved and I
for one hope the cause can be found and action taken to prevent such a
tragic loss of young lives in the future.
Much speculation has been made in the Media (and elsewhere) as to why (if?)
the TCAS system directed the Boeing pilot to descend when the Tupolev was
already in descent.
From doing a google search it seems that there have been a number of
occasions where a TCAS system has incorrectly directed a pilot to make a
maneuver that has put two aircraft on a direct collision course. It is only
through the skill and judgment of the pilots (And perhaps good visibility)
that a disaster has been averted.
It should also be remembered that last night's tragedy occurred during
darkness..maybe if visibility had been better disaster could have been
Without wishing to pre-judge any investigation, serious attention needs to
be paid to the TCAS system on board the aircraft and pilots need to be made
aware that these systems are far from infallible.
More on previous TCAS "incidents" here:
Midair Collision Danger
We spent hours and hours
cruising happily over continents like India, China, Russia and other places
where the communication could be improved (This is an understatement!) and
it is frightening to see todays accuracy of our on board navigation-systems
with opposite traffic. In the older days (Before GPS/IRS DME update) you
could spot this traffic somewhere left or right of your own track. These
days there is no more "left or right", it is right on the nose.
Now, taking into
consideration that some of this opposite traffic has no TCAS, in some cases
no transponder, and in the worst case scenario flies with an altimeter in
meters, using a manual slide ruler to "translate" meters into feet, it needs
no further explanation that it would be nice to have an additional
horizontal separation from your mere 1,000 - 2,000 feet vertical separation.
We would therefore like
you to consider the
perhaps for publication in some sort since the implementation of the
procedure is of such a simplicity that we wonder why this hasn't been done
After having circulated
this idea amongst some of our colleagues we realized that some companies are
already following this "offset system" as a sort of in-house SOP.
It would be a good idea if
all companies would follow this procedure over the above mentioned areas or
at least be aware of the fact that some companies are already following this
If we would have to draw a
parallel with the present situation we would construct a nice super
highspeed highway with just one white line in the middle and all the traffic
in both directions centering on this line, hoping that nobody comes roaring
around the corner.
mid-air between a Kazahk Il-76 and a Saudia 747 highlights a concern which
we have been discussing between ourselves for months. While all the details
may not apply; this disaster does dramatically illustrate our concern.
onboard GPS and/or DME updated IRS/INS navigational equipment has greatly
enhanced the ease and accuracy of aircraft navigation. However, under
certain circumstances, this accuracy could become a flight safety hazard.
Airline pilots spent untold hours EXACTLY in the centre of their 10 mile
wide airways guaranteed only 1000 or 2000 feet separation from opposite
direction traffic. If there is a mistake during an altitude change by the
crew of either aircraft, by the controller, with the communication between
the two, or an autoflight equipment failure -- a disaster may occur.
navigation computers should be off set just 1 or 2 miles to the right of
track. This would guarantee 2 to 4 miles lateral separation between opposite
direction traffic while all aircraft would still remain well within airways.
This would utilise the extreme accuracy of onboard navigational systems to
both remain within airways and to provide additional traffic separation. Had
both aircraft been equipped with TCAS, the Delhi disaster would have been
prevented. However, all aircraft world-wide are not so equipped.
pilots almost daily will pass another aircraft with this 1000 feet
clearance. Wouldn't it be much safer to also have at least 2 miles lateral
separation? Since equipment and people do fail, why not implement this
LESSONS FROM DELHI
12 months ago now, the
IFALPA Flight Safety Committee recommended that, (and I quote): "- all
aviation GPS and other air navigation equipment of comparable accuracy
contain a small embedded offset to the right that will protect against this
increased risk of head-on collision. This offset should be built directly
into the equipment, so that no operator procedure is required. The offset
would be cancelled only for approaches, at a suitable point in the
In the same article, the
Committee notes that "..for the first time, the probable navigation error
may well be contained within the dimensions of the airframe"
and "If two aircraft are
flying on reciprocal tracks using GPS, and they do not have adequate
vertical separation, they will almost assuredly collide."
Anyone who has seen
aircraft repeatedly go directly over or under them up to a thousand miles
from the nearest navigation beacon will have no difficulty agreeing with
this very sobering assessment.
Now, given the proximity
to Delhi and the types of aircraft involved, I accept that IRS/GPS accuracy
was unlikely to have been a major factor in this incident (if a factor at
all). However I would suggest that a high proportion of pilots reading this
fly aircraft that are IRS or GPS-equipped. Therefore, can I suggest that you
ALL start pressuring your individual airline's management and Flight Safety
Departments to institute this suggestion by IFALPA without delay? - and go
one pressuring them until they do something about it?
Having something like this
approved by the many regulatory authorities who will want to become involved
will take some time, (I'd suggest years!), even before such a change can be
written into commercial FMS databases. In the meantime, why not speak to
your Fleet Captain and Flight Safety Departments about having your airline
amend their SOPs to have crews write in a ONE MILE RIGHT OFFSET into their
IRS/GPS on passing through 10,000' in the climb. If everyone with IRS/GPS
does it, we will be doubling the separation. I have spoken to ICAO regulator
about this, and he is very much in favour of it, and I know a number of
pilots in my own airline are doing it - including this little black duck.
I know there are a lot of
you out there who don't fly IRS-equipped aircraft and I also appreciate that
this is not a panacea. Nothing is, but anything that reduces the risk of
another disaster like the Saudi/Kazhak collision has to be worth pursuing.
Disaster pilot failed to change altitude: official
July 2 2002
The pilot of a Russian passenger plane that collided in mid-air with a
cargo aircraft over southern Germany, killing at least 71 people, failed to
respond to repeated calls to change altitude, a state official said today.
Most of the victims were children under 18, the duty manager at Moscow's
Domodedovo airport was reported by Reuters as saying.
``All in all, there were about 50 children, including eight aged up to 12
years old,'' Stanislas Borovov told the agency.
Baden Wuerttemberg Transport Minister Ulrich Mueller said the Bashkirian
Airlines pilot had failed to respond to repeated calls to change altitude.
Quoting details given by Swiss air traffic controllers tracking the planes,
he said: "So we have to suppose that the pilot made a mistake."
The Tu-154 with 69 people aboard collided with a DHL Boeing 757 transport
plane cargo and two crew at an altitude of around 11,000 metres above Lake
Konstanz on the German-Swiss border shortly before midnight last night.
Mueller said the pilot of the cargo plane had tried to take evasive action
but was unable to avoid the crash.
Carlo Bernasconi, the head of the Skyguide company charged with air traffic
in Switzerland, would not confirm Mueller's statement but said that an
inquiry was under way.
Mueller said the Russian plane's flight recorder had been found and that no
dangerous materials were being transported in the cargo plane. "So there is
no danger to the population," he said.
The Bashkirian Airlines Tu-154 had been en-route to Barcelona from Moscow,
when it collided with the DHL Boeing 757 cargo aircraft with two crew at an
altitude of around 11,000 metres over Lake Konstanz last night.
Witnesses near the lake, which borders Switzerland and Austria, reported
hearing a loud explosion and seeing flaming pieces of wreckage crashing
towards the ground.
'Sky was on fire'
"The sky became bright all of a sudden. It looked as if the sky was on
fire," said Klaus Barinka, 42, a ferry boat captain working at Lake Konstanz.
State officials said it appeared the pilot of the passenger plane had failed
to respond to repeated calls to change altitude by Swiss air traffic
Unconfirmed reports said that the cargo plane crashed into the lake and that
an engine from one of the aircraft landed in a garden.
The smell of aviation fuel was thick at the scene, where hundreds of rescue
service workers and firefighters were at work while police combed an area
north of the town of Ueberlingen with helicopters.
Hospitals in the region were also on standby.
In Moscow, Interfax news agency quoted the emergencies ministry as saying
that 57 passengers and 12 crew were aboard the Tu-154, which flew out of
Moscow at 10:48 pm.
The ministry also said eight children were among the passengers.
German officials had earlier feared as many as 150 people were on board the
An airport official in Barcelona said today that the plane was carrying
Russian tourists heading for Spain's Costa Brava coastal resort area.
Wreckage spread over 30k
Wreckage and bodies were reported to be spread over a 30-kilometre area in
what was largely agricultural land.
"We have to fear the worst, that is that all the people are dead, said local
official Siegfried Tann.
Tann said spot fires broke out as flaming wreckage hit the ground, but that
most of them have been brought under control.
Police said several houses, a farm and a school had been set alight.
Officials at an emergency centre at the scene said at least 11 bodies had
been found and that a flight data recorder from one of the two planes had
been recovered in woodland by the lake.
The DHL Boeing cargo plane, operated by Bahrain Aviation and flying from
Bergamo in northern Italy to Brussels with only two crew aboard, and the
passenger aircraft collided shortly after 11:30 pm (0730 AEST Tuesday),
Air traffic control alarm
At press conference early today, Baden-Wuerttemberg state Transport Minister
Ulrich Mueller said Swiss air traffic controllers had been following the two
aircraft and noticed that they were flying at the same altitude.
The Tupolev failed to react to repeated calls to change altitude, while the
captain of the Boeing tried without success to avoid a collision, Mueller
Tupolev TU-154 carried 69 passengers
The Tu-154 had earlier made a stopover in the southern city of Munich.
In a statement to the press, DHL said it was far too early to speculate on
the possible cause of the accident but that a full and thorough
investigation was under way.
DHL said its thoughts were with families and friends of those who have
either lost their lives or been seriously injured in such tragic
The fleet of Bashkirian Airlines, one of the companies that has spun off
from the national carrier Aeroflot, is largely made up of Tu-154 aircraft
and is the flag carrier for the Republic of Bashkortostan, part of the
High-altitude mid-air collisions are rare, despite Europe's increasingly
Most large aircraft flying at such high cruising altitudes carry
transponders such as the Traffic Alert and Collision Avoidance System
(TCAS), which ensures pilots keep a safe distance from other planes in their