The German Midair – Lessons to be Learned
By now most of us have seen the press and industry accounts of the
tragic midair collision between a DHL 757F and a Bashkirian Airlines
Tupolev 154 over southern Germany, killing all 71 aboard both aircraft.
Like many accidents, it resulted after a chain of events, any link of
which, if broken, would have prevented the accident. And the scenario
leading up to the collision was eerily similar to an event in the skies
over Japan in January of 2001.
The latest RA I had was this situation where
normally an aircraft was descending to level 110
and the other one (not on my freq) cleared to
climb to FL100. The trouble was that the pilot
(an American) was climbing to 10 000 feet on the
QNH, which was pretty high that day:1028. And as
this plane had been on another frequency I had
absolutely no way to know or even have a clue of
what was happening, so when I heard this "TCas
Climb" I was surprised, maybe shocked ...but
happy afterwards that the pilot followed his
We have to remind ourselves that TCAS is not
meant to provide separation (the way controllers
see it, (like 3NM or 1000 ft) but to prevent
collision. The Uberlingen collision has taught
us that: whether you're pilot or a controller,
don't ever argue with TCAS!
The problem of TCAS awareness for controllers is
linked to the very short term action of a TCAS
RA, which doesn't really leave enough time for
the pilot to advise ATC of the RA in a timely
manner. In fact, when a pilot hears a
resolution, he is only 30 seconds away from
collision, so definitely his first priority is
to take action and unfortunately not to advise
ATC. That's where, as someone has already said,
a special and automatic squawk could be useful
but then, still it would depend on the speed of
the ATC radar sweep and range-scale.
One last thing, to those who have read the
report from Uberlingen, one thing noticed is the
that the Tupolev crew numbers five . Can you
imagine the complexity of CRM between five ? It
might have played a minor role in this - but it
also emphasizes the responsibility of the
As of this writing, this much is known:
- Both aircraft were operating at the same Flight Level (FL360) in
European RSVM airspace (1000’ vertical separation). Both aircraft were
equipped appropriately for participation in Europe’s RSVM airspace (
CADC’s, servoed altimeters, etc., and TCAS (version 7.0 – see sidebar)).
- Both aircraft had been handed off to “Skyguide”, the Swiss ATC agency
controlling southern Germany.
- Just prior to entering Skyguide's airspace, the “conflict resolution”
software function of the enroute radar was turned off for routine
maintenance. Existing Skyguide regulations call for two controllers to
be monitoring airspace under these circumstances, and increased
Many RAs (probably much more than 50% of them)
are "nuisance advisories" and occur when ATC
have provided the correct separation. In an
en-route environment, this may merely be an
minor annoyance, because it's quite unlikely
that there'll be anything else in your way. In a
terminal environment however, a nuisance RA can
quickly put an aircraft in much more danger than
it was in before TCAS intervened.
separation. One of the two controllers on duty was on break during the
- Parts of the main telephone system at Skyguide were also down for
maintenance at the time of the accident sequence.
- The one controller on duty was working an enroute sector and an
approach sector at the time of the accident. There were problems related
to the phone system in contacting the tower of the approach sector.
- An adjoining sector (Karlsruhe ATCC) was warned of the impending loss
of separation by its conflict alert system. When it observed no action
being taken, they attempted, with no avail, to contact Skyguide (phone
- Both aircraft received RA’s (TCAS Resolution Advisory) as designed –
The Russian aircraft was instructed by TCAS to Climb, the DHL to
descend. The DHL aircraft started its descent and transmitted so to ATC.
Almost simultaneous with the initial TCAS issued RA to climb, the
Russian aircraft was instructed by ATC to descend. There was a repeated
ATC instruction, and the Russian aircraft descended to comply with the
ATC instruction, overriding the TCAS RA command to climb (however, the
latest information showed the Russian aircraft climbing 100 feet prior
to the descent – possibly indicting that the aircraft initially
responded to the RA, and then chose to descend on ATC command)..
- Unfortunately, the lateral geometry was perfect for the collision
(more on this later).
Break any of the events in that chain, and the accident would have not
occurred. Or, had the lessons of the Japanese extremely near miss the
previous year been widely disseminated and trained for, this event may
not have occurred.
The Japanese Near Miss
On January 31, 2001, JAL Flight 907, a Boeing 747, had departed Tokyo-Haneda
with a destination of Naha. JAL Flight 958, a DC-10, was en route from
Pusan to Tokyo-Narita. A trainee controller cleared flight 907 to climb
to FL390. Two minutes later, JAL958 reported at FL370.
Both flights were
on an intersecting course near the Yaizu NDB (near Suruga Bay). The
controller noticed the imminent conflict, but instead of ordering Flight
958 (DC-10) to descend, he mistakenly ordered Flight 907 (747) to
descend. Immediately after this instruction, the crew of the flight 907
(747) were given a aural TCAS Resolution Advisory to climb in order to
avoid a collision. At the same time, the crew of Flight 958 (DC-10) were
given an aural TCAS advisory to descend. The captain of flight 907 (747)
followed the instruction of the air traffic controller to descend
instead of his TCAS RA to climb. A collision was averted when the pilot
of the 747 put his aircraft into a steep descent (fortunately there was
visual contact with other aircraft). The 747 missed the DC-10 by 105 to
165 meters in lateral distance, and 20 to 60 meters in altitude
difference. About 100 crew and passengers aboard the 747 sustained
injuries due the emergency maneuver.
it worse is that the JAL incident occurred in Jan 01, with
the Japanese authorities drawing the attention of ICAO to
the incident and asking for guidance. ICAO responded guess
when, August 02, one month after Ueberlingen.
Missed Opportunity to break the causal chain
PROBABLE CAUSE: The Aircraft and Railway Accident Investigation
Commission concluded that the air traffic controllers error and the
pilots decision to follow air traffic control instructions instead of
the TCAS Resolution Advisory (RA) were the two main causes.
Lessons to be learned
The major lesson to be learned from these events is:
ALWAYS FOLLOW THE INSTRUCTIONS ISSUED IN A TCAS RESOLUTION ADVISORY (RA)
If your TCAS issues a RA, Air Traffic Control has already failed. At
this point, the TCAS system is infinitely more valuable than ATC’s
instructions. Most enroute radars have update rates between 6 and 10
seconds – the information your TCAS is providing is much more timely
and, by design, training, and regulation, takes precedence over ATC
Both the Russians and the Japanese, in their respective
accident/incident, believed that ATC commands had priority over TCAS
commands and were apparently trained accordingly. My guess it that this
will be a favorite training scenario with many airlines around the world
in the very near future.
THE ONLY WARNING THAT HAS PRIORITY OVER A TCAS RA IS A GPWS/EGPWS
According to Honeywell, for TCAS to do its job properly and insure
separation, an RA must be complied with within 5.0 seconds and a G
loading (+/-) .25 G’s. If an RA command is reversed (version 7.0),
compliance requires a response within 2.5 seconds and a G loading of
(+/-) .35 G’s . The autopilot should be turned off to accomplish an RA
Some other considerations when using TCAS:
- Today’s avionics suites provide such precise lateral navigation, that
in some ways it may contribute to the possibility of a near miss/midair
On a number of occasions
I've seen serious incidents caused by TCAS when aircraft
started off properly separated. Example: DC-10 was cleared
to 4000 ft and pilot announced "TCAS, descending". The only
traffic within several miles of that aeroplane was one
climbing to 3000 ft underneath. TCAS, not knowing that the
outbound was going to stop at 3000 ft and the inbound at
4000 ft had decided that the best action was to get the DC10
down fast - the wrong decision because what was a 100% safe
situation developed into a loss of separation.
I have also experienced TCAS RAs causing loss of separation
in holding patterns - where an inbound a/c joining a hold is
descending rapidly... and also with outbound a/c climbing up
rapidly under a holding pattern. Until there is data
exchange between the ground and the TCAS such incidents will
TCAS is a most useful tool which has undoubtedly saved
lives, but please don't ever in your wildest dreams believe
that every RA is caused by an ATC (or aircrew) foul up.
is ever (or always) so clearcut
lack of vertical
separation. Some routes/procedures may allow for offsets.
- Always communicate as soon as possible to ATC that you are climbing/descending
in response to a Resolution Advisory. Future plans are for Mode S/ADSB
transmission to ATC of an RA and it’s command, but for now, ATC has no
idea why you are climbing/descending in response to a TCAS command.
- Do not try to use TCAS for lateral separation maneuvers. TCAS was designed
for vertical separation maneuvers only. Limits on current generation TCAS
antennae’s and processors allow for approximate azimuth information (may
up to 30 degree error in azimuth at close ranges).
- While TCAS version 7.0 eliminates many of the false warnings associated
with earlier versions, it is still recommended, particularly in 1000’
separation RSVM airspace, to have a reduced rate of climb/descent for
the last 1000 feet of one’s climb/descent to assigned altitude, to prevent
a possible overshoot and possible issuance of a RA (version 7.0 adds a
slight time delay to avoid false warnings).
- Unfortunately, our current TCAS installations (747,757/767, most 727’s)
range display capabilities. While the software is looking out to the maximum
range of TCAS design, the crews cannot see a conflict developing as they
could on a longer range display. The 757/767 fleet is due to be upgraded
shortly with a longer range display.
- The first response to a “traffic, traffic” TCAS TA (Traffic Advisory)
warning should be an attempt to visually identify the other aircraft.
Keep in mind that azimuth information displayed on your TCAS display may
be up to 30 degrees off.
- As reported in a previous article on runway incursions, there is a documented
TCAS “save” by using TCAS information in a way not intended by the original
designers. After the runway collision in Linate, Italy between a Cessna
Citation and an SAS MD-87 in low visibility, the tower controller, unaware
of the collision on the runway, issued a takeoff clearance to a Lufthansa
jet. The Lufthansa crew did not observe the just departed SAS aircraft
on its TCAS, and queried the controller as to its whereabouts. It subsequently
refused takeoff clearance, almost certainly saving another collision (wreckage
was on the runway).
As always, the Aircraft Operating Manual is the primary source for operating
procedures for the TCAS unit and procedures installed on your aircraft.
Currently, the procedures outlined in the 757/767 A.O.M. are:
TA’s – PF observes TCAS display and begins visual search. PNF calls out
range, bearing and altitude of the intruder and joins visual search.
RA’s – PF clears airspace when conducting avoidance maneuver and alters
vertical speed to move VSI needle out of the red and into the green “fly
to” zone. PNF continues visual search, monitors intruder position on TCAS
and verifies that PF is correctly following the RA. PF expeditiously returns
to assigned flight path when clear of conflict (note: to prevent additional
TA/RA from not being at assigned altitude).
ARINC Link (pdf) (TCAS Industry Alert Bulletin - August 12, 2002)
this link (by Shore Guy)
From an ATC point of
view, the situation in which the controller found himself that night was
a total management failure. Alone with a degraded radar system, main
telephone out of service, wrongly programmed back up telephone,
unscheduled inbound to a normally closed airfield at night forcing him
to open a separate position with a different frequency , leaving him 2
frequencies and 2 radar pictures to monitor on 2 positions several
meters apart. Short term conflict alert disabled, etc…
He spotted the
conflict late, issued an "expedite descent" clearance to the TU154 ( as
it was anyway coordinated lower with adjacent centre) and when he saw
the Mode C of the TU154 winding down , he considered the problem solved.
What he did not know is that the 757 had already started his descent as
the radar return rate on that degraded mode was very slow. The 757 FO
was PNF ( doing the R/T) and had left the cockpit leaving the Capt alone
at the time of the RA, so he did not warn ATC immediately. When F/O came
back 23 seconds later, he informed ATC using a wrong call sign, but
irrelevant since the transmission was blocked by the A320 inbound to FH
on the other frequency. (the controller later admitted he did not hear
the 757 call ).
There you go.
Without knowing that any of the aircraft was following an RA , the ATC
clearance issued was a solution that should have solved the conflict in
the mind of the controller.
But even If both pilots had reported they were following an RA, the
controller would have said nothing as ATC is supposed to stop issuing
instructions (and be responsible for anti collision) after that point .
Without ATC , no collision. without TCAS no collision, if they would
have been IMC , probably no collision.
Small things , errors, or small deviations from procedures,
insignificant if taken in isolation ,are causing a tragedy when put in a
certain sequence. Mixing automated systems with humans decisions is not
and never will be a good choice.
Are we so sure this will never happen again ? I doubt it.
TCAS is far from being perfect and will contribute mathematically to
more collisions. ( I recall hearing from MITRE Corp in the US, the
owners of the software, something like for every 30 collisions it saves,
TCAS will cause one ).
BFU Factual Report
link Dealing with
Risk in Air Traffic Control (and Other Safety Fables)
two prior links ONE