German collision was the first of the TCAS era

 - April 23, 2008, 7:44 AM

At 11:35 p.m. on July 1, two transport-category aircraft collided over the northern shore of Lake Constance near the town of Ueberlingen, Germany, at the Swiss border. Sixty-nine passengers and crew aboard a Tupolev Tu-154M owned and operated by Bashkirian Airlines (BAC) were killed when it collided with DHL Flight 611, a scheduled cargo flight in a Boeing 757-200 freighter. The two DHL pilots, the only occupants onboard, were also killed. The accident has the distinction of being the world’s first midair collision with both aircraft having operating airborne collision avoidance systems (ACAS), better known in North America as traffic alert and collision avoidance systems (TCAS). It was also the first midair collision over Europe since 1976.

BAC is a scheduled and charter passenger and cargo operator based in Ufa, Bashkortostan, a Russian republic in the southern Ural Mountains. The Tu-154M (RA85816) had a crew of 12 onboard including four pilots, a navigator, an engineer, two technicians and four flight attendants. The 52-year-old captain, Aleksandr Gross, was a Russian citizen but German by nationality. He was multilingual and had good English-speaking skills. A 12,000-hr pilot,  Gross had about 4,000 hr in international operations.

All the passengers were citizens of the Russian Federation, living in Bashkiria. They included five adult chaperones accompanying 52 academically gifted students, all under the age of 16, on a trip to Spain sponsored by the Bashkirian UNESCO committee.

The Boeing 757-200 (A9C-DHL) was a freighter and its crew consisted of captain Paul Phillips of the UK and first officer Brant Campioni of Canada. DHL International is a subsidiary of DHL Worldwide Express, a Belgium-based company.

Both aircraft were cruising at their assigned altitude of 36,000 ft. The Tu-154 was westbound en route from Ufa, Bashkiria Republic, Russia to Barcelona with stops at Moscow and Munchen. The Boeing was going northbound on a flight from Bahrain via Bergamo to Brussels. Both aircraft were converging on, and due to cross over, Lake Constance. Both had been transferred to Zurich ATC a few minutes prior to the collision.

TCAS Worked as Advertised

German investigators have released some details of the cockpit voice recorder (CVR) tape that revealed both aircraft TCAS systems were issuing traffic warnings with the Tupolev crew hearing “Climb, climb...” simultaneous to the 757 crew hearing, “Descend... descend...” According to the CVR, the crew of the Tu-154 received conflicting instructions almost simultaneously. Within seconds of getting their initial TCAS resolution advisory (RA) to climb, the Swiss Skyguide controller instructed them to “descend Flight Level 350, expedite, I have crossing traffic.”

The crew of the Tu-154 did not respond and 14 seconds later Skyguide told them to “…descend Level 350, expedite descent” at which time Gross acknowledged the instruction and, contrary to the onboard RA, complied with the ATC instruction
to descend. Thirty-one seconds later the Tu-154 hit the DHL aircraft at 35,400 ft as the Boeing was complying with its TCAS RA to descend out of 36,000 ft.

German accident investigation authorities (BFU) were still analyzing the information from both CVRs and flight data recorders (FDR) at their facility in Braunschweig as of press time. Russian investigators and a team from the U.S. National Transportation Safety Board are supporting their efforts. It has been reported that only the 757’s FDR was in “good condition” but it appeared all of both aircraft’s voice and data recorders would yield their information.

Skyguide confirmed its short-term conflict alert (STCA) system went down for maintenance at approximately 11 p.m. local time and was inoperative at the time of the accident. The controller was handling five aircraft on two radar screens, including an aircraft on a separate frequency flying an instrument approach to Friedrichshafen Airport. The second controller assigned to assist the controller in charge was on break.

At the same time, a controller for Germany’s Deutsche Flugsicherung (DFS), who was on duty in the Karlsruhe ATC center, observed the conflict. The DFS controller repeatedly tried to call Skyguide, but the telephone was initially busy and then went unanswered. It was learned that Skyguide’s primary telephone line was out of order and the Skyguide controller was using the reserve phone line up to two minutes prior to the accident, attempting to call the tower at Friedrichshafen.

According to BFU when the STCA is out of service the lateral separation requirement increases to seven nautical miles, up from five, with a standard 1,000-ft vertical separation. Accordingly, the Skyguide controller should have given the Tu-154 instructions at least 90 sec before the crash occurred. In fact, the controller did not issue his first avoidance instruction until 44 sec prior to impact. Both aircraft were on the same frequency but only the Tupolev was given an air-traffic-conflict warning by Skyguide.

It is known that the 757 had the latest TCAS version, a Honeywell TCAS 2000 version 7. This model is programmed to reverse the RA if it detects the other aircraft has taken the wrong action to avoid a collision. It was not clear at press time if the crew of the 757 received a revised RA.

While the nature of the training received by the Russian pilot is as yet unknown, BAL general director Nikolai Odegov has stated the aircraft was in compliance with current European standards and equipped with TCAS and equipment complying with the standards for reduced vertical separation.

A spokesman for the Russian government announced that it was standard operating procedure under Russian regulations that the pilot in command has the final authority as to the appropriate course of action. He also noted that most domestic Russian aircraft are not TCAS-equipped, so pilots historically are conditioned to follow ATC commands.

According to Denis Chagnon, a spokesman for the International Civil Aviation Organization, ICAO Standards provide the general regulatory context for ACAS, while ICAO Procedures provide specific parameters in the operation of the systems. “These two sets of documents establish that the pilot-in-command has full authority and full responsibility to select the course of action that will best resolve a traffic conflict and avert a collision, including the use of ACAS,” Chagnon told AIN.

ICAO Annex 2–Rules of the Air, section 3.2.2. states, “The aircraft that has the right-of-way shall maintain its heading and speed, but nothing in these rules shall relieve the pilot-in-command of an aircraft from the responsibility of taking such action, including collision avoidance maneuvers based on resolution advisories provided by ACAS equipment, as will best avert collision.”

Chagnon said, “At the moment, there is no international standard which deals with a conflict between an ACAS RA and ATC instructions. This issue was addressed by ICAO, however, in proposed training objectives issued by the organization for the consideration of member states in the preparation of initial and recurrent training programs for pilots.”

According to Item 12 of page E-10 of ICAO’s Proposed ACAS Performance-based Training Objectives, “if pilots simultaneously receive instructions to maneuvers from ATC and an RA which are in conflict, the pilot should follow the RA.”

Stuart Matthews, president of the Flight Safety Foundation, told AIN, “We may never know why the Tu-154 pilot elected to descend when TCAS was telling him to climb, but the poor guy was in a dilemma. The troubling human factors issue once again raised its ugly head. Why would he choose to ignore the most up-to-the-second, on-scene information for the disembodied voice of someone far away?…In the U.S. and Europe the culture is such that pilots have no problem ignoring ATC and trusting an RA, but that may not be so true in Russia; I really don’t know. But it is for certain that no one thing causes an accident, it’s always a chain of events.”

Matthews stressed that if you can break the chain, you can prevent the accident. He pointed out there were very clear links involved, including only one controller working multiple flights on two radar scopes and two frequencies, the STCA was turned off and even the telephone was busy. “I don’t necessarily blame the pilot because I don’t know all the facts,” Matthews said, “but at the end of the day he was the last link of the unbroken chain.”