The Investigators Speak

ASW: In the accident airplane, is there anything in its operational, or electrical or maintenance history that indicated there might have been something in the way of a looming electrical problem?

Vic Gerden, (TSB investigator in charge): The short answer is no. We did look at the maintenance history of the aircraft in detail, and there wasn't anything pointing to a discrepancy or problem that would lead to this accident. (ASW note: The overall reliability of the MD-11 does not compare favorably with other aircraft, based on service difficulty reports. Although the accident MD-11 was not included, 34 sister aircraft in U.S. service showed a sixfold greater rate of problems with in-flight entertainment systems compared to 197 B757 and B767 aircraft; see box below).

ASW: The photo shown at the press conference of the arcing in the bundle shows evidence of a full-blown arc, not a ticking fault. Did the circuit protector fail to protect?

Gerden: The arc that we showed [at the press conference] was magnified 22 times. In fact, it is barely visible to the naked eye. It was a very small arc site. It did not trip the circuit breaker. The same phase on that power cable arced further downstream, about 50 centimeters or 20 inches.

ASW: How many? As the fire is spreading, it's eating into more circuits, so now some of the other breakers might be going off line.

Gerden: Yes, sooting was found on some other breakers. Those trips were caused by thermal tripping from the fire.

Jim Foot (TSB systems group chairman for the SR 111 investigation): You know the white indicator ring on the end of a circuit breaker? We found some of those that were sooted. So obviously they tripped before impact. They were a variety from the overhead circuit breaker panel.

ASW: Vic, you mentioned that the crew lost most of their instruments. Could you be more specific? Did they lose all six of the glass- cockpit displays, for example?

Gerden: They lost five for sure. They would have had a red 'X' there. There are indications that they attempted to restore information that would have appeared on DU 2 [display unit #2, the center one in front of the captain]. That would have been partial information. So other than that they had standby instruments. The compass was up on the windshield, between the two front windscreens and had to be pulled down, and it was a pretty basic compass. And the other standby instrumentation was not ideally set up, but it was all they had. By the time the airplane impacted the water, the 'OFF' flag was on the standby indicator.

ASW: What are you and your [TSB] colleagues looking at to give an assured power supply to the standby instrument?

Gerden: We issued an advisory in September 2001 dealing with the position, the size and the additional independent power supply for the standby instru-ment, as well as additional training for the crews.

ASW: Has any of that taken root in the industry?

Gerden: Swissair certainly made changes. They put in an integrated display of standby instruments with a backup power supply. Other companies have installed that same integrated standby instrument in their MD-11s.

ASW: You mentioned that it was not possible for Capt. Urs Zimmermann and First Officer Stefan Loew to have gotten the airplane down to a landing. Did you explore an emergency descent, not relying on the FMS [flight management system], just raw data, no fuel dump, and accept the fact of an overweight landing?

Gerden: The calculation we did was just that. Under ideal conditions, the minimum descent time and landing, with everything working, and fuel dumping would be immaterial - you could do that if you wanted to - but in terms of the minimum time to descend and land, it would have taken 13 minutes from the ideal 'start of descent' point. That would take them to 10:27 p.m. By 10:24 p.m. the systems already were starting to fall off line and the cockpit environment was deteriorating pretty rapidly after 10:25. So the answer is unfortunately no.

ASW: On troubleshooting, in trying to determine whether it is air conditioning or something more serious, what are your thoughts on locating smoke detectors in the air conditioning ducts to at least get a 'yes' or a 'no' on that as the first order of business?

Gerden: We're not normally in the business of creating the solutions or attempting to go beyond identifying the safety deficiency. We did make recommendations in terms of the requirement for built-in smoke detectors and suppression equipment. A big adjunct to that is what the crews should have in terms of training and procedures and access into areas so they can have an aggressive program in place to locate what the problem is and to deal with it as early as possible, and at the same time to prepare the airplane to land expeditiously. It depends on where they are over the world - they may not be able to land.

ASW: The U.S. National Transportation Safety Board issued recommendations last year associated with the problems of detection and suppression of fire in inaccessible spaces, and the UK's Air Accidents Investigation Branch has cited the problem. When the TSB recommends that we need better coverage in inaccessible areas, how far do you have in mind - all inaccessible areas?

Gerden: This is a function of the design of the aircraft and the risks associated with where the electrical and wiring components are vis-a-vis combustible materials, so it would probably vary from one airplane to the next.

ASW: You alluded to deficiencies in circuit breaker design. Could you be more specific?

Foot: The breakers used now are all thermal. They don't catch some of the arc faults, which don't have enough current to drive the circuit breaker to trip. The newer ones can catch a very small arcing event within the first few cycles of it taking place. That's a huge safety advance.

ASW: Are you referring to the arc fault circuit interrupter technology?

Foot: Yes.

ASW: Have you indicated when you would like to see that sort of technology deployed in commercial aircraft?

Gerden: We haven't put a time frame on that in the recommendation that was issued. As soon as feasible.

ASW: It was interesting to hear the TSB's call for a cockpit video recorder. How might that have helped in the investigation?

Gerden: It could capture switch positions, displays, circuit breaker trips, and it could capture the cockpit environment. A picture is worth a thousand words.

ASW: What timeline were you looking for regarding installation of cockpit video?

Gerden: The technology is available. It's a matter of getting the will.

Foot: EUROCAE (European Organization for Civil Aviation Equipment) has put together a standard. It will be coming out soon.

Gerden: From an accident investigation perspective, having it in sooner rather than later is the objective.

ASW: You envision cockpit video recording not only for new production aircraft but also a hard mandate to retrofit into the existing fleet?

Gerden: Our preference would be to have a retrofit.

ASW: You indicated a need for a more comprehensive testing standard for the thermal acoustic insulation material. The FAA developed the radiant panel test after the Flight 111 accident. You alluded to the need to go beyond that test. What did you have in mind?

Gerden: That test primarily is designed for a thin film material. There are other materials that are not thin film, that are foams and thicker materials. They may not be appropriately tested by that one single radiant heat panel test. We're suggesting additional tests for all types of materials used for thermal acoustic insulation blankets.

ASW: Would you be looking at smokiness, toxicity, what?

Gerden: Our approach is that the material should not sustain or propagate fire. If it doesn't sustain a fire then toxicity or smoke are not a problem.

ASW: On the wiring, you referenced the limitation of the 60� vertical flame test on an unpowered wire. What would you like to see in terms of more realistic testing?

Gerden: In our August 2001 recommendations, we called for a test regime that evaluates the wire and its failure characteristics under realistic operating conditions (e.g., powered), so the goal is to prevent the risk of ignition, and the corollary is to minimize damage in adjoining areas.

ASW: What additional policies or practices with respect to wire installation, separation and segregation come to mind as a result of this investigation?

Gerden: The safety concern is that the criteria used need to be more specific and clear as to what wire separation is acceptable.

ASW: Is it possible to remove all the flammable materials used in the construction of a modern jetliner and install non-flammable materials?

Gerden: It's possible to remove the MPET material. That order has been put out there. But there are other ways of mitigating the risk, by having built in detectors, by having an in-flight firefighting plan. The problem needs to be tackled on many fronts.