We Americans, at the time, tended to place the blame for this midair squarely on the Russian pilots. But that was unfair. While U.S. regulations clearly stated that in the event of a disagreement between a TCAS Resolution Alert and Air Traffic Control instructions, pilots were to follow the TCAS. The ICAO regulations at the time were silent on the subject.
— James Albright
A year and a half prior to this midair, on 31 January 2001, two Japan Airlines Boeing 747s nearly collided over Japan in nearly identical circumstances. Both aircraft received proper TCAS resolution alerts but a trainee air traffic controller gave one of the planes conflicting instructions. The pilots spotted each other and managed to avoid collision by only 35 feet. Nine passengers and two crew were seriously injured during the violent evasive maneuvering. The Japanese government asked ICAO for guidance. ICAO decided to leave the rules up to individual governments.
After the DHL/Bashkirian midair, ICAO rules were changed. See TCAS for more about this.
As sad as this incident is, there is an additional tragic postscript. The air traffic controller working two screens with inoperative phones and radar and warning systems off line without his knowledge was hounded by the press and eventually murdered by a distraught father of one of the victims.
Lesson learned? Well we who started our TCAS careers in the United States continue to do as we always have: follow TCAS resolutions alerts over those of air traffic control. ICAO now agrees. (ICAO terminology calls the system Airborne Collision Avoidance System, ACAS.) It is also worth noting that just because you have TCAS doesn't mean you don't need to clear the skies with your eyes and your ears. More about this: The Big Sky Theory.
- Date: 01 JUL 2002
- Time: 23:35
- Type: Boeing 757-23APF
- Operator: DHL Aviation
- Registration: A9C-DH
- Fatalities: 2 of 2 crew, no passengers
- Aircraft Fate: Destroyed
- Phase: En route
- Airports: (Departure) Bergamo-Orio Al Serio Airport (BGY/LIME), Italy; (Destination) Brussel-Zaventem Airport (BRU/EBBR), Belgium
- Type: Tupolev 154M
- Operator: Bashkirskie Avialinii
- Registration: RA-85816
- Fatalities: 9 of 9 crew, 60 of 60 passengers
- Aircraft Fate: Destroyed
- Phase: En route
- Airports: (Departure) Moskva-Domodedovo Airport (DME/UUDD), Russia; (Destination) Barcelona Airport (BCN/LEBL), Spain
At 21:21:50 hrs, the PIC contacted ACC Zurich on the frequency 128.050 MHz at FL 260 and in direct approach to the waypoint ABESI. At 21:21:56 hrs, the transponder code 7524 was assigned. With the identification of the airplane a clearance for a direct approach to the TANGO VOR as well as for a climb from FL 260 to FL 320 was given. The PIC requested to climb to FL 360, which was approved approximately four minutes later at 21:26:36 hrs. At 21:29:50 hrs the airplane reached this flight level, without the pilots reporting it.
At 21:34:30 hrs the copilot handed over the control of the airplane to the PIC in order to go to the lavatory installed in a cubicle at the rear of the cockpit. At 21:34:31 hrs the PIC confirmed that he had taken over.
At 21:34:42 hrs the airborne TCAS alarmed the crew about possibly conflicting traffic by a Traffic Advisory (TA): “traffic, traffic". After the TA the CVR recorded clicking noises. 14 seconds later (21:34:56 hrs) TCAS issued a Resolution Advisory (RA) “descend, descend".
Approximately two seconds later the autopilot (AP) was switched off, the control column pushed and the thrust of the engines reduced. FDR data shows that the pitch was reduced from 2.5° to approximately 1.5° and the vertical acceleration lowered from about 1.0 g to 0.9 g. According to the FDR and the TCAS recordings the airplane had reached a rate of descent of 1500 ft/min 12 seconds after the autopilot had been switched off.
At this time the copilot had returned to his work station and put on his headset. His reaction to the RA was recorded as "increase". Following this RA, the rate of descent was changed and reached approximately 2600 ft/min 10 seconds later. During the descent the pitch angle decreased to –1° and the powerplant thrust was reduced to approximately 1.2 (EPR).
According to the CVR at 21:35:14 hrs a Master Caution Aural Warning is heard for two seconds. According to the FDR the autothrottle was switched off by the crew at 21:35:18 hrs.
At 21:35:19 hrs the crew reported the “TCAS descent“ to ACC Zurich. Subsequently the copilot requested the PIC twice to descend. Once with the word “descend“ (21:35:26 hrs) and then by saying “descend hard“ (21:35:30 hrs).
Approximately two seconds prior to the collision the control column was pushed fully forward.
Source: AX001-1-2/02, §1.1.1
At 21:11:55 hrs - near Salzburg still over Austrian territory - the crew received the clearance from Vienna radar for a direct approach to the Trasadingen VOR at FL 360. At 21:16:10 hrs, the airplane entered German airspace and was controlled by Munich Radar. At 21:29:54 hrs, the crew was instructed by Munich to change over to ACC Zurich on 128.050 MHz. At 21:30:11 hrs and at FL 360 the PNF contacted ACC Zurich. At 21:30:33 hrs, ACC Zurich assigned the transponder code 7520 to the airplane, which was acknowledged 6 seconds later.
For the time between about 21:33:00 hrs and 21:34:41 hrs the CVR recorded crew discussions concerning an airplane approaching from the left which was displayed on the vertical speed indicator (VSI/TRA) which is part of the TCAS. All flight crew members with the exception of the flight engineer were involved in these discussions. These recordings suggest that the crew strived to localize the other airplane as to its position and its flight level. At 21:34:36 hrs, the commander stated: “Here it is in sight“, and two seconds later: “Look here, it indicates zero“. During the time from 21:34:25 hrs to 21:34:55 hrs, the airplane turned at a bank angle of approximately 10° from a magnetic heading (MH) of 254° to 264°.
At 21:34:42 hrs, TCAS generated a TA (“traffic, traffic“). The CVR recorded that both the PIC and the copilot called out “traffic, traffic“.
At 21:34:49 hrs - i.e. seven seconds later - ACC Zurich instructed the crew to expedite descent to FL 350 with reference to conflicting traffic (“...... descend flight level 350, expedite, I have crossing traffic“). While the controller was giving the instruction - the radio transmission took just under eight seconds - the PIC requested the PF to descend. At 21:34:56 hrs, the control column was pushed forward, the autopilot (pitch channel) was switched off and the powerplant thrust reduced to approximately 72 % (N1). FDR data shows a reduction of the pitch angle of the airplane from 0° to approximately –2.5° as well as a reduction of the vertical acceleration from approximately 1 g (normal acceleration of the earth near the airplane centre of gravity) to 0.8 g.
The instruction to descend was not verbally acknowledged by the crew. At the same time (21:34:56 hrs) TCAS generated an RA (“climb, climb“). At 21:34:59 hrs, the CVR recorded the voice of the copilot stating: “It (TCAS) says (говорит): “climb“. The PIC replied: “He (ATC) is guiding us down“. The copilot's enquiring response: “descend?“
At 21:35:02 hrs, (six seconds after the RA “ climb, climb”) the PF pulled the control column. As a result, the rate of descent ceased to increase. The vertical acceleration rose from 0.75 g to 1.07 g. The engine thrust remained unchanged in conjunction with this control input (refer to Appendix 5a).
At 21:35:03 hrs, the engine throttles were pulled back further.
The discussion between the crew members was interrupted at 21:35:03 hrs by the controller instructing the crew once again to expedite descend to FL 350 (“... descend level 350, expedite descend“).This instruction was immediately acknowledged by the PNF. The controller then informed the crew about other flight traffic at FL 360 in the 2 o’clock position (“...Ya, … we have traffic at your 2 o’clock position now at 3-6-0“) and the PIC asked: “Where is it?“, the copilot answered: “Here on the left side!“. At the time, the rate of descent was approximately 1 500 ft/min. The voice of the flight navigator can be heard on the CVR saying:" It is going to pass beneath us!" while the controller was giving his last instruction.
At 21:35:04 hrs the roll channel of the autopilot was switched off. At 21:35:05 hrs, the PF pushed the control column again and the rate of descent increased to more than 2 000 ft/min.
At 21:35:24 hrs TCAS issued an RA “increase climb“. The copilot commented this with the words: “It says ‘climb”! At the time of the RA „increase climb“, the FDR recorded a slow movement of the control column nose down leading to a change in pitch angle from –1° to approximately –2° and in a reduction in vertical acceleration. The descent rate was approximately 1800 ft/min (refer to Appendix 5b).
Five seconds before the collision the control column was pulled back, associated with a minor increase of thrust levers setting.
During the last second before the collision the control column was pulled back abruptly and the thrust levers were pushed fully forward.
Source: AX001-1-2/02, §
Regulations of the Boeing crew
The operational basics, regulations and procedures are defined in the Operations Manual, Part A, Section 8 dated 4 February 2002.
Flight crews should follow the RAs using established procedures unless doing so would jeopardize the safe operation of the airplane or positive visual contact confirms that there is a safer course of action. If an RA occurs, expeditiously accomplish the following:
If maneuvering is required, disengage the autopilot and smoothly adjust pitch and thrust to satisfy RAs.
The pitch must be adjusted to fly the airplane symbol just out of the red region(s) on the attitude indicator or to achieve a vertical speed just outside the red band(s) on the RA VSI/TRA (as installed). Adjust thrust as required to maintain desired speed.
Attempt to establish visual contact:
When clear of conflict, advise ATC and smoothly return to previous clearance.
Source: AX001-1-2/02, pp. 62 - 63
At the time, this was standard operating procedure for most, but not all operators worldwide. In the U.S. the rules are to follow the TCAS RA, even if it conflicts with ATC.
Regulations of the Tupolev crew
The operational basics, regulations and procedures for the handling of equipment and systems are defined in the Flight Operational Instruction for the TU154M („РУКОВОДСТВО ПО ЛЕТНОЙ ЭКСПЛУАТАЦИИ ТУ154M“).
En-route flight: After reaching the en-route flight level switch the range over to 40 NM and N (normal coverage). [This sentence is followed by the following items under the title “ATTENTION“:] 1. Prior to following the resolution advisory it is necessary to get contact with the conflicting traffic.
Source: AX001-1-2/02, pp. 64 - 65
At the time the ICAO did not mandate a procedure one way or the other, the rules the Tupolev crew were under said listen to ATC, don't follow the RA unless you "get contact" with the conflicting traffic.
Air traffic control
When the controllers reported for duty at 17:50 hrs, they were not aware of the fact that during the night shift extensive sectorisation work on the sectors of the upper airspace was scheduled. Documents concerning the planned work were available for self briefing. They did not seize the opportunity to read them even though the duty schedule and their work contract allow time for such reading. The effects of this omission remain relatively insignificant as the documents did not include a description as to how the planned work would affect the availability of the technical equipment.
After the sectorisation work had started and the air traffic volume had decreased one of the controllers retired to rest in the lounge. Normally he would have returned to the control room early in the morning when air traffic increases, unless unusual circumstances would require his presence earlier. The spatial distance between the lounges and the control room prevents a quick alert of the second controller in conjunction with an immediate appearance. Thus the remaining radar controller had to assume the tasks of the radar planning controller (RP) and the radar executive controller (RE) and if necessary the tasks of the supervisor (DL) at the same time.
Officially this procedure did not exist, but had been in practise at ACC Zurich for many years. This arrangement made the night shifts for the controllers more comfortable. This is a way of proceeding which does not provide any redundancy of human resources so that procedural errors, wrong distributions of attention or the omission of important actions may lead to hazardous situations as nobody is there to notice these mistakes and to take corrective actions. It follows that the breaks prescribed could not be taken. Even though it was an unofficial procedure it was known to and tolerated by the management.
When the TU154M crew contacted Zurich at 21:30:11 hrs for the first time and also reported the flight level, the controller did not notice that the B757-200 had just reached the same flight level and that both airplanes were approaching each other at right angles. The distance between the two airplanes was still approximately 64 NM. If he had noticed the situation he would have instructed the TU154M crew to descend to FL 350. The control strip showed this altitude after Trasadingen VOR anyhow.
At the time the controller concentrated on a delayed Airbus A320 approaching Friedrichshafen airport. In doing so, he had to move to the adjacent workstation. He tried to phone Friedrichshafen several times. This was not possible due to a technical defect in the by-pass phone system but was time consuming and bound his concentration. He was not informed about the additional presence of a SYMA and therefore did not consider to involve him even though the SYMA would have been able to suggest an alternative.
Thus he neglected the control of the two other airplanes over a certain period of time. He was not alerted of the impending collision risk because the optical STCA was not available.
When the controller instructed the TU154M crew at 21:34:49 hrs for the first time to expedite descent to FL 350 the horizontal separation was practically already below 7 NM (exactly at 21:34:56, when the controller’s radio message ended).
The TU154M should have descended to FL 350 by 21:34:56 hrs to ensure a vertical separation of 1 000 ft in the RVSM airspace. To achieve this it would have been necessary to give the instruction to descend to FL 350 at 21:33:49 hrs at the latest - i.e. one minute before this instruction was actually given. This time is based on a normal rate of descent of approximately 1 000 ft per minute.
When the TU154M crew did not verbally respond to the first instruction to descend to FL 350, the controller repeated this instruction at 21:35:03 hrs more emphatically. As in his first instruction to descend he used the term “expedite“. The addition “expedite“ did not signalise, however, that the separation had already been infringed. The wording “I have crossing traffic“ which he used with his first instruction to descend did not match the urgency of the situation. It would have been better to use the term “immediately“ instead of “expedite“. A more detailed information about the conflicting traffic, e.g. “you have crossing traffic at 360 (or same level) in your 10 o’clock position“ or “from left to the right at 360 (or same level) distance: ........... NM“ would have been more appropriate in view of the short distance between the two airplanes (distance approximately 5.5 NM).
When the controller observed on the left monitor (RP) that the TU154M had initiated the descent he considered the problem solved and once again turned to the right monitor (RE). The reason was that the crew of the Airbus A320 approaching Friedrichshafen had just called again on 119,920 MHz. The two airplanes (B757-200 and TU154M) with the pertinent data were displayed on the right monitor as well. Only for radio transmissions on the different frequencies it was necessary to change workstations (between RP and RE).
When the controller moved to the workstation RE in order to deal with the A320, he concentrated his whole attention on the Airbus. Thus he neither noticed the descent of the B757-200 nor did he hear the radio message of the crew reporting a TCAS descent at 21:35:19 hrs.
When the controller had solved the problem with the Airbus A320, he once again concentrated his attention on the two airplanes. At this time, the collision had already happened and he saw the TU154M being displayed as a red point on the radar monitor indicating that a radar signal was not received any more. His radio calls addressed to the TU154M at 1:36:01, 21:36:23, and at 21:37:17 hrs remained unanswered. The B757-200 was no longer displayed on the radar monitor; it was not called by the controller.
It is the BFU's opinion that the controller was not in a position to safely execute the transferred and additionally assumed tasks.
A reason was the insufficient number of air traffic controllers during the night shift resulting from the duty schedule which did not ensure a continuous staffing of the workstations. It would have been the duty of the management and the quality assurance of the air navigation service company to realize these deficiencies and to take appropriate corrective actions. In addition the above-mentioned institutions tolerated the current practice applied to the conduct of the night shift.
Another reason was that priorities had not been evaluated properly. Dividing his attention on two events he found himself in a situation the effects of which he underestimated and ultimately could not control.
The Zurich ACC was contracted out to a private company, Swiss Air Navigation Services. They normally had two controllers and two assistants on duty at night, but one controller and assistant normally retired to a lounge once traffic flow decreased to a point where all concerned the load could be handled by one controller team.
At the time of this mishap, the ICAO did not mandate a procedure to follow the Resolution Advisory. Most country rules, including the ones the DHL crew were operating under, did place a priority of the RA over ATC instructions.
The following immediate causes have been identified:
- The imminent separation infringement was not noticed by ATC in time. The instruction for the TU154M to descend was given at a time when the prescribed separation to the B757-200 could not be ensured anymore.
- The TU154M crew followed the ATC instruction to descend and continued to do so even after TCAS advised them to climb. This manoeuvre was performed contrary to the generated TCAS RA.
The following systemic causes have been identified:
- The integration of ACAS/TCAS II into the system aviation was insufficient and did not correspond in all points with the system philosophy. The regulations concerning ACAS/TCAS published by ICAO and as a result the regulations of national aviation authorities, operational and procedural instructions of the TCAS manufacturer and the operators were not standardised, incomplete and partially contradictory.
- Management and quality assurance of the air navigation service company did not ensure that during the night all open workstations were continuously staffed by controllers.
- Management and quality assurance of the air navigation service company tolerated for years that during times of low traffic flow at night only one controller worked and the other one retired to rest.
Source: AX001-1-2/02, §3.2
The ICAO rules were changed to reflect what the U.S. (and most of the world) already had in place.
c) in the event of an RA, pilots shall:
1) respond immediately by following the RA as indicated, unless doing so would jeopardize the safety of the aeroplane;
Note 1.— Stall warning, wind shear, and ground proximity warning system alerts have precedence over ACAS.
Note 2.— Visually acquired traffic may not be the same traffic causing an RA. Visual perception of an encounter may be misleading, particularly at night.
2) follow the RA even if there is a conflict between the RA and an air traffic control (ATC) instruction to manoeuvre;
3) not manoeuvre in the opposite sense to an RA;
Note.— In the case of an ACAS-ACAS coordinated encounter, the RAs complement each other in order to reduce the potential for collision. Manoeuvres, or lack of manoeuvres, that result in vertical rates opposite to the sense of an RA could result in a collision with the threat aircraft.
4) as soon as possible, as permitted by flight crew workload, notify the appropriate ATC unit of the RA, including the direction of any deviation from the current ATC instruction or clearance;
Note.— Unless informed by the pilot, ATC does not know when ACAS issues RAs. It is possible for ATC to issue instructions that are unknowingly contrary to ACAS RA indications. Therefore, it is important that ATC be notified when an ATC instruction or clearance is not being followed because it conflicts with an RA.
5) promptly comply with any modified RAs;
6) limit the alterations of the flight path to the minimum extent necessary to comply with the RAs;
7) promptly return to the terms of the ATC instruction or clearance when the conflict is resolved; and
8) notify ATC when returning to the current clearance.
Note.— Procedures in regard to ACAS-equipped aircraft and the phraseology to be used for the notification of manoeuvres in response to an RA are contained in the PANS-ATM (Doc 4444), Chapters 15 and 12 respectively.
Source: ICAO Doc 8168 Vol 1 PANS OPS, §III, Chapter 3, ¶3.2. c)
German Federal Bureau of Aircraft Accidents Investigation, AX001-1-2/02, 1 July 2002, (near) Ueberlingen/Lake of Constance/Germany, Boeing 757-200 and Tupolev TU154M
May Day: Deadly Crossroads, Cineflix, Episode 10, Season 2, 13 February 2005 (DHL 611)